ASTM D888-18

Standard Test Methods for Dissolved Oxygen in Water

SIGNIFICANCE AND USE
4.1 Dissolved oxygen is required for the survival and growth of many aquatic organisms, including fish. The concentration of dissolved oxygen may also be associated with corrosivity and photosynthetic activity. The absence of oxygen may permit anaerobic decay of organic matter and the production of toxic and undesirable esthetic materials in the water.
SCOPE
1.1 These test methods cover the determination of dissolved oxygen in water. Three test methods are given as follows:    
Range, mg/L  
Sections  
Test Method A—Titrimetric Procedure–High Level  
>1.0  
8 – 15  
Test Method B—Instrumental Probe Procedure—Electrochemical  
0.05 to 20  
16 – 25  
Test Method C—Instrumental Probe Procedure—Luminescence-Based Sensor  
0.05 to 20  
26 – 31  
1.2 The precision of Test Methods A and B was carried out using a saturated sample of reagent water. It is the user's responsibility to ensure the validity of the test methods for waters of untested matrices.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For a specific precautionary statements, see 7.1 and Note 17.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Apr-2018
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

Relations

• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D1066-18e1 - Standard Practice for Sampling Steam
• Effective Date: 01-Aug-2018
• Refers: ASTM D1066-18 - Standard Practice for Sampling Steam
• Effective Date: 01-Aug-2018
• Refers: ASTM D2777-12 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jun-2012
• Refers: ASTM D1066-11 - Standard Practice for Sampling Steam
• Effective Date: 15-Jun-2011
• Refers: ASTM D3370-10 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2010
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D3370-08 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Oct-2008
• Refers: ASTM D2777-08 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jan-2008
• Refers: ASTM D3370-07 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2007
• Refers: ASTM D1066-06 - Standard Practice for Sampling Steam
• Effective Date: 15-Dec-2006
• Refers: ASTM D1129-06a - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06ae1 - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D2777-06 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Aug-2006
• Refers: ASTM D1193-06 - Standard Specification for Reagent Water
• Effective Date: 01-Mar-2006

Overview

ASTM D888-18: Standard Test Methods for Dissolved Oxygen in Water provides comprehensive procedures for determining dissolved oxygen (DO) levels in various types of water. Developed by ASTM International, this standard is essential for water quality assessment, regulatory compliance, and environmental monitoring. Dissolved oxygen concentrations are crucial for the survival and growth of aquatic organisms, assessing water corrosivity, evaluating photosynthetic activity, and preventing anaerobic conditions that can produce harmful by-products.

This standard outlines three primary test methods for DO measurement:

• Test Method A: Titrimetric Procedure for high-level dissolved oxygen (above 1.0 mg/L)
• Test Method B: Instrumental Probe Procedure using electrochemical sensors (range: 0.05 to 20 mg/L)
• Test Method C: Instrumental Probe Procedure using luminescence-based sensors (range: 0.05 to 20 mg/L)

Key Topics

1. Importance of Dissolved Oxygen

• Critical for aquatic life and biological processes
• Indicator of water quality and ecosystem health
• Associated with potential corrosivity and photosynthetic processes

2. Methods of Measurement

• Titrimetric (Winkler-based) Method: Widely used for high concentrations; applicable to streams and sewage samples
• Electrochemical Probes: Enable continuous, in-situ monitoring with rapid response; suitable for various types of natural and industrial waters
• Luminescent Probes: Offer high sensitivity and low detection limits; less prone to certain chemical interferences

3. Sample Collection and Preservation

• Proper sample collection techniques are critical to prevent DO changes before analysis
• Recommendations for bottles, handling, and, where necessary, chemical preservatives

4. Quality Control and Calibration

• Emphasis on using reagent-grade chemicals and calibration standards
• Verification of instrument accuracy and method blanks to ensure data validity

5. Interference and Limitations

• Chemical substances, such as nitrites, iron, and reactive sulfur compounds, can affect results; specific reagents or procedures may be needed to eliminate these interferences
• User responsibility to validate methods for unique sample matrices

Applications

ASTM D888-18 is widely used by:

• Environmental Laboratories: For routine monitoring of rivers, lakes, groundwater, and wastewater
• Water Treatment Facilities: To ensure effective process control and regulatory compliance
• Aquaculture and Fisheries Management: Monitoring DO to maintain healthy aquatic environments
• Industrial Process Monitoring: Controlling DO in boilers, cooling water, and chemical production
• Field Investigations: Portable probes enable instant DO analysis during site surveys and remediation work

These methods are designed for flexibility and adaptability, supporting both laboratory and field-based applications. They are critical tools for maintaining water quality, supporting aquatic life, and meeting environmental regulations.

Related Standards

ASTM D888-18 references and aligns with several related ASTM standards, enhancing its scope and reliability in water analysis:

• ASTM D1066: Practice for Sampling Steam
• ASTM D1129: Terminology Relating to Water
• ASTM D1193: Specification for Reagent Water
• ASTM D2777: Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• ASTM D3370: Practices for Sampling Water from Closed Conduits
• ASTM D5847: Practice for Writing Quality Control Specifications for Water Analysis Methods
• ASTM E200: Practice for Preparation, Standardization, and Storage of Standard Solutions

These referenced standards ensure a robust framework for water sample handling, reagent preparation, and analytical reliability.

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Keywords: dissolved oxygen, water quality, ASTM D888, titrimetric method, electrochemical probe, luminescence sensor, environmental monitoring, water testing, regulatory compliance, aquatic organisms, laboratory analysis, field testing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D888 − 18
Standard Test Methods for
Dissolved Oxygen in Water
This standard is issued under the fixed designation D888; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* D1129Terminology Relating to Water
D1193Specification for Reagent Water
1.1 Thesetestmethodscoverthedeterminationofdissolved
D2777Practice for Determination of Precision and Bias of
oxygen in water. Three test methods are given as follows:
Applicable Test Methods of Committee D19 on Water
Range, mg/L Sections
D3370Practices for Sampling Water from Closed Conduits
Test Method A—Titrimetric >1.0 8–15
Procedure–High Level D5847Practice for Writing Quality Control Specifications
Test Method B—Instrumental Probe 0.05 to 20 16–25
for Standard Test Methods for Water Analysis
Procedure—Electrochemical
E200Practice for Preparation, Standardization, and Storage
Test Method C—Instrumental Probe 0.05 to 20 26–31
Procedure—Luminescence-Based of Standard and Reagent Solutions for ChemicalAnalysis
Sensor
1.2 The precision of Test MethodsAand B was carried out
3. Terminology
using a saturated sample of reagent water. It is the user’s
3.1 Definitions:
responsibility to ensure the validity of the test methods for
3.1.1 For definitions of terms used in this standard, refer to
waters of untested matrices.
Terminology D1129.
1.3 The values stated in SI units are to be regarded as
3.2 Definitions of Terms Specific to This Standard:
standard. No other units of measurement are included in this
3.2.1 amperometric systems, n—those instrumental probes
standard.
that involve the generation of an electrical current from which
1.4 This standard does not purport to address all of the
the final measurement is derived.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.2.2 instrumental probes, n—devices used to penetrate and
priate safety, health, and environmental practices and deter- examineasystemforthepurposeofrelayinginformationonits
mine the applicability of regulatory limitations prior to use. properties or composition.
For a specific precautionary statements, see 7.1 and Note 17.
3.2.2.1 Discussion—The term probe is used in these test
1.5 This international standard was developed in accor-
methods to signify the entire sensor assembly, including
dance with internationally recognized principles on standard-
electrodes, electrolyte, membrane, materials of fabrications,
ization established in the Decision on Principles for the
and so on.
Development of International Standards, Guides and Recom-
3.2.3 potentiometric systems, n—those instrumental probes
mendations issued by the World Trade Organization Technical
inwhichanelectricalpotentialisgeneratedandfromwhichthe
Barriers to Trade (TBT) Committee.
final measurement is derived.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
4.1 Dissolved oxygen is required for the survival and
D1066Practice for Sampling Steam
growth of many aquatic organisms, including fish. The con-
centration of dissolved oxygen may also be associated with
These test methods are under the jurisdiction of ASTM Committee D19 on
corrosivity and photosynthetic activity.The absence of oxygen
Water and are the direct responsibility of Subcommittee D19.05 on Inorganic
Constituents in Water. may permit anaerobic decay of organic matter and the produc-
Current edition approved May 1, 2018. Published May 2018. Originally
tion of toxic and undesirable esthetic materials in the water.
ɛ1
approved in 1946. Last previous edition approved in 2012 as D888–12 . DOI:
10.1520/D0888-18.
5. Purity of Reagents
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.1 Purity of Reagents—Reagent grade chemicals shall be
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. used in all tests. Unless otherwise indicated, it is intended that
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D888 − 18
all reagents shall conform to the specifications of the Commit- through a tube extending to the bottom of a 250 to 300 mL
teeonAnalyticalReagentsoftheAmericanChemicalSociety. biological oxygen demand (BOD) bottle. Fill the bottle to
Other grades may be used if it is first ascertained that the overflowing and prevent turbulence and the formation of
reagent is of sufficiently high purity to permit its use without bubbles while filling the bottle.
lessening the accuracy of the determination.
7. Preservation of Samples
5.1.1 Reagent grade chemicals, as defined in Practice E200,
shall be used unless otherwise indicated. It is intended that all
7.1 Do not delay the determination of dissolved oxygen.
reagents conform to this standard. Samples for Test Method A may be preserved 4 to8hby
adding 0.7 mL of concentrated sulfuric acid (sp gr 1.84) and
5.2 Unless otherwise indicated, reference to water shall be
1.0 mL of sodium azide solution (20 g/L) to the bottle
understood to mean reagent water conforming to Specification
containing the sample in which dissolved oxygen is to be
D1193, Type I. Other reagent water types may be used
determined. Biological activity will be inhibited and the
provided it is first ascertained that the water is of sufficiently
dissolved oxygen retained by storing at the temperature of
high purity to permit its use without adversely affecting the
collection or by water sealing (inverting bottle in water) and
bias and precision of the test method. Type II water was
maintaining at a temperature of 10 to 20°C. Complete the
specified at the time of round robin testing of this test method.
determination as soon as possible, using the appropriate
6. Sampling procedure for determining the concentration of dissolved
oxygen. (Warning—Sodium azide is highly toxic and multa-
6.1 CollectthesamplesinaccordancewithPracticesD1066
genic. Follow manufacturerâs instruction for handling and
and D3370.
storage.)
6.2 For higher concentration of dissolved oxygen, collect
the samples in narrow mouth glass-stoppered bottles of TEST METHOD A
300-mL capacity, taking care to prevent entrainment or solu-
TITRIMETRIC PROCEDURE—HIGH LEVEL
tion of atmospheric oxygen.
8. Scope
6.3 With water under pressure, connect a tube of inert
8.1 Thistestmethodisapplicabletowaterscontainingmore
material to the inlet and extend the tube outlet to the bottom of
than1000µg/Lofdissolvedoxygensuchasstreamandsewage
thesamplebottle.Usestainlesssteel,Type304or316,orglass
samples. It is the user’s responsibility to ensure the validity of
tubing with short neoprene connections. Do not use copper
the test method for waters of untested matrices.
tubing, long sections of neoprene tubing, or other types of
polymeric materials. The sample line shall contain a suitable
8.2 This test method, with the appropriate agent, is usable
cooling coil if the water being sampled is above room
with a wide variety of interferences. It is a combination of the
temperature, in which case cool the sample 16 to 18°C. When
WinklerMethod,theAlsterberg(Azide)Procedure,theRideal-
a cooling coil is used, the valve for cooling water adjustment
Stewart (permanganate) modification, and the Pomeroy-
shall be at the inlet to the cooling coil, and the overflow shall
Kirshman-Alsterberg modification.
be to a point of lower elevation. The valve for adjusting the
8.3 The precision of the test method was carried out using a
flow of sample shall be at the outlet from the cooling coil.The
saturated sample of reagent water.
sampleflowshallbeadjustedtoaratethatwillfillthesampling
vessel or vessels in 40 to 60 s and flow long enough to provide
9. Interferences
a minimum of ten changes of water in the sample vessel. If the
9.1 Nitrite interferences are eliminated by routine use of
sampling line is used intermittently, flush the sample line and
sodium azide. Ferric iron interferes unless 1 mL of potassium
cooling coil adequately before using.
fluoridesolutionisused,inwhichcase100to200mg/Lcanbe
6.4 Where samples are collected at varying depths from the
tolerated. Ferrous iron interferes, but that interference is
surface, a special sample bottle holder or weighted sampler
eliminated by the use of potassium permanganate solution.
with a removable air tight cover should be used.This unit may
High levels of organic material or dissolved oxygen can be
be designed to collect several 250 or 300 mL samples at the
accommodated by use of the concentrated iodide-azide solu-
same time. Inlet tubes extending to the bottom of each bottle
tion.
andthewaterafterpassingthroughthesamplebottleorbottles
10. Apparatus
displacesairfromthecontainer.Whenbubblesstoprisingfrom
thesampler,theunitisfilled.Watertemperatureismeasuredin
10.1 Sample Bottles, 250 or 300 mL capacity with tapered
the excess water in the sampler.
ground-glass stoppers. Special bottles with pointed stoppers
andflaredmouthsareavailablefromsupplyhouses,butregular
6.5 For depths greater than 2 m, use a Kemmerer-type
types (tall or low form) are satisfactory.
sampler. Bleed the sample from the bottom of the sampler
10.2 Pipettes, 10-mL capacity, graduated in 0.1-mL divi-
sions for adding all reagents except sulfuric acid. These
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
pipettes should have elongated tips of approximately 10 mm
listed by the American Chemical Society, see Analar Standards for Laboratory
foraddingreagentswellbelowthesurfaceinthesamplebottle.
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Only the sulfuric acid used in the final step is allowed to run
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. down the neck of the bottle into the sample.
D888 − 18
NOTE 3—If the full bottle technique is used, 3.9007 g must be used to
11. Reagents
make 0.0375 N.
11.1 Alkaline Iodide Solutions:
NOTE 4—If sodium thiosulfate is used, prepare and preserve a 0.1 N
solutionasdescribedinNote1.Determinetheexactnormalitybytitration
11.1.1 Alkaline Iodide Solution—Dissolve 500 g of sodium
against 0.025 N potassium biiodate solution. Dilute the appropriate
hydroxide or 700 g of potassium hydroxide and 135 g of
volume (nominally 250 mL) of standardized 0.1 N Na S O solution to 1
2 2 3
sodium iodide or 150 g of potassium iodide (KI) in water and
L. One millilitre of 0.025 N thiosulfate solution is equivalent to 0.2 mg of
dilute to 1 L. Chemically equivalent potassium and sodium
oxygen. If the full bottle technique is followed, use 37.5 mL of sodium
salts may be used interchangeably. The solution should not thiosulfate solution and standardize to 0.0375 N.
give a color with starch indicator when diluted and acidified.
11.5 Starch Solution—Make a paste of6gof arrowroot
Store the solution in a dark rubber-stoppered bottle. This
starch or soluble iodometric starch with cold water. Pour the
solution may be used if nitrite is known to be absent and must
paste into 1 L of boiling water. Then add 20 g of potassium
be used if adjustments are made for ferrous ion interference.
hydroxide, mix thoroughly, and allow to stand for 2 h. Add 6
11.1.2 Alkaline Iodide-Sodium Azide Solution I—This solu-
mL of glacial acetic acid (99.5%). Mix thoroughly and then
tion may be used in all of these submethods except when
add sufficient HCl (sp gr 1.19) to adjust the pH value of the
adjustment is made for ferrous ion. Dissolve 500 g of sodium
solution to 4.0. Store in a glass-stoppered bottle. Starch
hydroxide or 700 g of potassium hydroxide and 135 g of
solution prepared in this manner will remain chemically stable
sodiumiodideor150gofpotassiumiodideinwateranddilute
for one year.
to 950 mL. To the cooled solution add 10 g of sodium azide
NOTE 5—Powdered starches such as thyodene have been found ad-
dissolved in 40 mL of water. Add the NaN solution slowly
equate. Some commercial laundry starches have also been found to be
with constant stirring. Chemically equivalent potassium and
usable.
sodiumsaltsmaybeusedinterchangeably.Thesolutionshould
NOTE 6—If the indicator is not prepared as specified or a proprietary
starch indicator preparation is used, the report of analysis shall state this
notgiveacolorwithstarchindicatorsolutionwhendilutedand
deviation.
acidified. Store the solution in a dark rubber-stoppered bottle.
(See 7.1.)
11.6 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid.
One millilitre neutralizes about 3 mL of the alkaline iodide
11.1.3 Alkaline Iodide-Sodium Azide Solution II—This so-
lution is useful when high concentrations of organic matter are reagent.
found or when the dissolved oxygen concentration exceeds 15
NOTE 7—Sulfamic acid (3 g) may be substituted.
mg/L. Dissolve 400 g of sodium hydroxide in 500 mL of
11.7 Potassium Fluoride Solution(400g/L)—Dissolve40g
freshly boiled and cooled water. Cool the water slightly and
of potassium fluoride in water and dilute to 100 mL. This
dissolve900gofsodiumiodide.Dissolve10gofsodiumazide
solution is used in the procedure for eliminating ferric ion
in40mLofwater.Slowlyadd,withstirring,theazidesolution
interference. Store this solution in a plastic bottle.
tothealkalineiodidesolution,bringingthetotalvolumeto1L.
(See 7.1.)
11.8 Potassium Oxalate Solution (20 g/L)—Dissolve2gof
potassium oxalate in 100 mL of water. One millilitre of this
11.2 Manganous Sulfate Solution—Dissolve 364 g of man-
solution will reduce 1.1 mL of the KMnO solution. This
ganous sulfate in water, filter, and dilute to 1 L. No more than
solution is used in the procedure for eliminating ferrous ion
atraceofiodineshouldbeliberatedwhenthesolutionisadded
interference.
to an acidified potassium iodide solution.
11.9 Potassium Permanganate Solution (6.3 g/L)—
11.3 Potassium Biiodate Solution (0.025 N)—Dissolve
Dissolve 6.3 g of potassium permanganate in water and dilute
0.8125 g of potassium biiodate in water and dilute to 1 L in a
to 1 L. With very high ferrous iron concentrations, solution of
volumetric flask.
KMnO should be stronger so that 1 mL will satisfy the
NOTE 1—If the bottle technique is used, dissolve 1.2188 g of biiodate
demand. This solution is used in the procedure for eliminating
in water and dilute to 1 L to make 0.0375 N.
ferrous ion interference.
11.4 Phenylarsine Oxide Solution (0.025 N)—Dissolve
12. Procedure
2.6005 g of phenylarsine oxide in 110 mL of NaOH solution
(12 g/L). Add 800 mL of water to the solution and bring to a
12.1 Elimination of Ferrous Ion Interference, If Necessary:
pH of 9.0 by adding HCl (1+1). This should require about 2
12.1.1 Add to the sample (collected as in 6.2) 0.70 mL of
mLof HCl. Continue acidification with HCl (1+1) until a pH
H SO , followed by 1.0 mL of KMnO solution. Where high
2 4 4
of 6 to 7 is reached, as indicated by a glass-electrode system.
iron is present, also add 1.0 mL of KF solution. Stopper and
Dilute to 1 L. Add 1 mL of chloroform for preservation.
mix by inversion. The acid should be added with a 1-mL
Standardize against potassium biiodate solution.
pipette graduated in 0.1-mL divisions. Add sufficient KMnO
solution to maintain a violet tinge for 5 min. If the color does
NOTE 2—Phenylarsine oxide is more stable than sodium thiosulfate.
not persist for 5 min, add more KMnO solution, but avoid
However, sodium thiosulfate may be used. The analyst should specify
which titrant is used. For a stock solution (0.1 N), dissolve 24.82 g of
excess. In those cases where more than 5 mL of KMnO
Na S O ·5H O in boiled and cooled water and dilute to 1 L. Preserve by
2 2 3 2
solution is required, a stronger solution of this reagent may be
adding 5 mLof chloroform. For a dilute standard titrating solution (0.005
used to avoid dilution of the sample.
N) transfer 25.00 mL of 0.1 N Na S O to a 500-mL volumetric flask.
2 2 3
12.1.2 After 5 min, completely destroy the permanganate
Dilute to the mark with water and mix completely. Do not prepare more
than 12 to 15 h before use. color by adding 0.5 to 1.0 mL of K C O solution. Mix the
2 2 4
D888 − 18
sample well, and allow it to stand in the dark. Low results are where:
causedbyexcessoxalatesoitisessentialtoaddonlysufficient
T = 0.025 N titrating solution required for titration of the
oxalate to completely decolorize the permanganate without
sample, mL.
having an excess of more than 0.5 mL. Complete decoloriza-
13.2 Use Eq 2 to convert to a standard temperature and
tion should be obtained in 2 to 10 min. If the sample cannot be
pressure measurement.
decolorized without a large excess of oxalate, the dissolved
A
oxygen results will be of doubtful value.
Dissolvedoxygen, mg/L 5 (2)
0.698
12.2 Add 2.0 mL of MnSO solution to the sample as
where:
collected in a sample bottle, followed by 2.0 mL of alkaline
iodide-sodium azide solution well below the surface of the A = oxygen at 0°C and 760 mm Hg, mL.
NOTE13—Eachmillilitreof0.0375 Ntitrantisequivalentto1mg/LO
liquid (see Note 8 and Note 9). Be sure the solution tempera- 2
when the full bottle technique is used.
ture is below 30°C to prevent loss due to volatility of iodine.
NOTE 14—If the percentage of saturation at 760-mm atmospheric
Carefullyreplacethestoppertoexcludeairbubblesandmixby
pressure is desired, the dissolved oxygen found is compared with
inverting the bottle several times. Repeat the mixing a second
solubility data from standard solubility tables, making corrections for
time after the floc has settled, leaving a clear supernatant barometric pressure and the aqueous vapor pressure, when necessary. See
Appendix X1.
solution. Water high in chloride requires a 10-min contact
period with the precipitate. When the floc has settled, leaving
14. Precision and Bias
at least 100 mL of clear supernatant solution, remove the
14.1 Theprecisionofthetestmethodwasdeterminedbysix
stopper, and add 2.0 mL of H SO , allowing the acid to run
2 4
operators in three laboratories, running three duplicates each
down the neck of the bottle. Restopper and mix by inversion
(not six laboratories as required by Practice D2777) using a
until the iodine is uniformly distributed throughout the bottle.
saturatedsampleofreagentwater.Themeanconcentrationwas
Titrate without delay 203 mL of original sample.Acorrection
9.0 mg/L, and the pooled single operator precision in these
is necessary for the 4 mL of reagents added (2 mL of MnSO
samples was 0.052 mg/L.
solution and 2 mL of alkaline iodide-sodium azide solution:
200×[300⁄(300−4)]=203 mL (see Note 10)).
14.2 Precision and bias for this test method conforms to
Practice D2777–77, which was in place at the time of
NOTE 8—Take care to use the correct alkaline iodide solution (11.1.1)
collaborative testing. Under the allowances made in 1.4 of
ifnonitriteispresentorferrousionwasoxidized,(11.1.2)fornormaluse,
or (11.1.3) if there is a high organic or dissolved oxygen concentration. Practice D2777–13, these precision and bias data do meet
existing requirements for interlaboratory studies of Committee
NOTE 9—Two millilitres of the alkaline iodide-sodium azide solution
are used to ensure better contact of the iodide-azide solution and sample
D19 test methods.
withlessagitation.With250-mLbottles,1mLoftheiodide-azidesolution
may be used if desired. In this procedure, as in the succeeding ones, all
15. Quality Control (QC)
reagents except the H SO are added well below the surface of the liquid.
2 4
15.1 To ensure that analytical values obtained using these
NOTE 10—In the case where ferrous ion interference has been
eliminated,atotalof6.7mLofreagentswereadded(0.7mLofacid,1mL
testmethodsarevalidandaccuratewithintheconfidencelimits
ofKMnO solution,2mLofMnSO solution,and3mLofalkalineiodide
4 4 of the test, the following QC procedures must be followed
solution). The volume of sample for titration is 203 mL. A slight error
when analyzing dissolved oxygen.
occursduetothedissolvedoxygenoftheKMnO solution,butratherthan
complicate the correction further, this error is ignored.
15.2 Calibration and Calibration Verification:
15.2.1 Standardize the titrating solution against the potas-
12.3 Rapidly titrate the 203 mL of sample with 0.025 N
sium biiodate solution.
titrating solution to a pale, straw yellow color.Add 1 to 2 mL
15.2.2 Verifytitratingsolutionbyanalyzingasamplewitha
of starch indicator. Continue the titration to the disappearance
known amount of the dissolved oxygen, if possible. The
of the blue color.
amount of the sample should fall within 615% of the known
NOTE11—Ifthefullbottletechniqueisused,transfertheentirecontents concentration.
of the bottle, 300 6 3 mL, to a 500-mLErlenmeyer flask and titrate with
15.2.3 If standardization cannot be verified, restandardize
0.0375 N titrating solution.
the solution.
NOTE 12—At the correct end point, one drop of 0.025 N KH(IO )
3 2
15.3 Initial Demonstration of Laboratory Capability:
solutionwillcausethereturnofthebluecolor.Iftheendpointisoverrun,
continue adding 0.025 N KH(IO ) solution until it reappears, noting the
15.3.1 Ifalaboratoryhasnotperformedthetestbefore,orif
3 2
volume required. Subtract this value, minus the last drop of KH(IO )
3 2
there has been a major change in the measurement system, for
(0.04 mL) from the volume of 0.025 N titrating solution used. Disregard
example,newanalyst,newinstrument,andsoforth,aprecision
the late reappearance of the blue color, which may be due to the catalytic
and bias study must be performed to demonstrate laboratory
effect of organic material or traces of uncomplexed metal salts.
capability.
13. Calculation
13.1 Calculate the dissolved oxygen content of the sample
Carpenter, J. H., “New Measurement of Oxygen Solubility in Pure and Natural
as follows: Water,” Limnology and Oceanography, Vol 11, No. 2, April 1966, pp. 264–277.
Supporting data have been filed atASTM International Headquarters and may
T 30.2
beobtainedbyrequestingResearchReportRR:D19-1070.ContactASTMCustomer
Dissolved oxygen, mg/L 5 31000 (1)
200 Service at [e-mail].
D888 − 18
15.3.2 Analyze seven replicates of the same solution. Each may contain dissolved or suspended solids. Samples can be
replicate must be taken through the complete analytical test analyzed in situ in bodies of water or in streams, or samples
method including any sample preservation and pretreatment can be collected and analyzed subsequent to collection. The
steps. electrochemical probe method is especially useful in the
15.3.3 Calculate the mean and standard deviation of the monitoring of water systems in which it is desired to obtain a
seven values and compare to the acceptable ranges of bias in continuous record of the dissolved oxygen content.
14.1. This study should be repeated until the recoveries are 16.2.1 This test method is recommended for measuring
within the limits given in 14.1. If an amount other than the dissolved oxygen in waters containing materials that interfere
recommended amount is used, refer to Practice D5847 for with the chemical methods, such as sulfite, thiosulfate,
information on applying the F test and t test in evaluating the polythionate, mercaptans, oxidizing metal ions, hypochlorite,
acceptability of the mean and standard deviation. and organic substances readily hydrolyzable in alkaline solu-
tions.
15.4 Laboratory Control Sample (LCS):
15.4.1 Air-saturated reference water samples may be used 16.3 Electrochemical dissolved oxygen probes are practical
for the continuous monitoring of dissolved oxygen content in
for laboratory control samples. The value obtained must fall
within the control limits established by the laboratory. natural waters, process streams, biological processes, and so
on, when the probe output is conditioned by a suitably stable
15.5 Method Blank:
electronic circuit and recorded. The probe must be standard-
15.5.1 Analyze a reagent water test blank with each batch.
ized before use on samples free of interfering materials,
The amount of dissolved oxygen found in the blank should be
preferably with the azide modification of Test Method A.
less than the analytical reporting limit. If the amount of
dissolvedoxygenisfoundabovethislevel,analysisofsamples
17. Summary of Test Method
is halted until the contamination is eliminated, and a blank
17.1 The most common instrumental probes for determina-
shows no contamination at or above this level, or the results
tion of oxygen dissolved in water are dependent upon electro-
mustbequalifiedwithanindicationthattheydonotfallwithin
chemical reactions. Under steady-state conditions, the current
the performance criteria of the test method.
or potential can be correlated with dissolved oxygen concen-
15.6 Matrix Spike (MS):
trations.
15.6.1 Dissolved oxygen is not an analyte that can be
feasibly spiked into samples. NOTE 15—Steady-state conditions necessitate the probe being in
thermal equilibrium with the solution, this typically taking 20 min for
15.7 Duplicate: 6
nonlaboratory conditions.
15.7.1 To check the precision of sample analyses, analyze a
17.1.1 Probes that employ membranes normally involve
sample in duplicate with each batch. The value obtained must
metals of different nobility immersed in an electrolyte that is
fall within the control limits established by the laboratory.
retained by the membrane. The metal of highest nobility (the
15.7.2 Calculate the standard deviation of the duplicate
cathode) is positioned at the membrane. When a suitable
values and compare to the precision determined by the labo-
potentialexistsbetweenthetwometals,reductionofoxygento
ratory or in the collaborative study using an F test. Refer to
hydroxide ion occurs at the cathode surface. An electrical
6.4.4ofPracticeD5847forinformationonapplyingthe Ftest.
current is developed that is directly proportional to the rate of
15.7.3 If the result exceeds the precision limit, the batch
arrival of oxygen molecules at the cathode.
must be reanalyzed or the results must be qualified with an
17.1.2 The thallium probe, which does not utilize a
indication that they do not fall within the performance criteria
membrane, exposes a thallium electrode to the water sample.
of the test method.
Reaction of oxygen with the thallium establishes a potential
15.8 Independent Reference Material (IRM):
between the thallium electrode and a reference electrode. The
15.8.1 Independent reference water samples may be ob-
potential is related logarithmically to dissolved oxygen con-
tained from commercial sources. The value obtained from
centration. The cell output decreases (theoretically 59 mV/
thesesamplesmustfallwithinthecontrollimitsestablishedby
decade at 25°C) with increased oxygen concentration.
the laboratory.
NOTE 16—The thallium probe has utility in waste treatment monitoring
systems; it has limited application under conditions of high dissolved
TEST METHOD B
oxygen (>8 mg/L) and low temperature (<10°C).
INSTRUMENTAL PROBE PROCEDURE—
17.1.3 The electronic readout meter for the output from
ELECTROCHEMICAL
dissolved oxygen probes is normally calibrated in convenient
16. Scope
scales (0 to 10, 0 to 15, or 0 to 20 mg/L) with a sensitivity of
approximately 0.05 mg/L. More sensitive dissolved oxygen
16.1 This test method is applicable to waters containing
ranges are practical through amplification in the electronic
dissolved oxygen in the range from 50 to 20000 µg/L. It is the
readout (including µg/L readings in boiler feed waters).
user’s responsibility to ensure the validity of this test method
for waters of untested matrices.
16.2 This test method describes procedures that utilize
D’Aoust, B. G., Clark, M. J. R., “Analysis of Supersaturated Air in Natural
electrochemical probes for the determination of dissolved
Waters and Reservoirs,” Transactions of the American Fisheries Society, Vol 109,
oxygen in fresh water and in brackish and marine waters that 1980, pp. 708–724.
D888 − 18
17.2 Interfacial dynamics at the probe-sample interface are of the thallium probe (approximately 60.05 mg/L dissolved
a factor in probe response. Turbulence should be constant or oxygen per pH unit). The performance of membrane probes is
abovesomeminimumlevelasrecommendedbytheinstrument not affected by pH changes.
manufacturer.
18.5 Dissolvedoxygenprobesaretemperaturesensitiveand
17.3 Response rates of dissolved oxygen probes are rela-
temperature compensation is normally provided by the manu-
tively rapid, often as fast as 99% in 15 s. Probe outputs may
facturer. The thallium probe has a temperature coefficient of
be recorded for continual monitoring or utilized for process
1.0mV/°C,membraneprobeshaveatemperaturecoefficientof
control (see Note 15).
4 to 6%⁄°C dependent upon the membrane employed.
18.6 Insoluble organic or inorganic materials that can coat
18. Interferences
the surface of dissolved oxygen probes will affect the perfor-
18.1 Dissolved organic materials normally encountered in
mance of either the thallium or membrane probes.
water are not known to interfere in the output from dissolved
oxygen probes.
19. Apparatus
18.2 Dissolved inorganic salts are a factor in the calibration
19.1 Amperometric Probes—Oxygen-sensitiveprobesofthe
of dissolved oxygen probe.
amperometric type are normally composed of two solid metal
18.2.1 Solubility of oxygen in water at a given oxygen
electrodes of different nobility in contact with a supporting
partial pressure changes with the kind and concentration of
electrolytethatisseparatedfromthetestsolutionbyaselective
dissolved inorganic salts. Conversion factors for seawater and
membrane. The current generated by the reduction of oxygen
brackish waters may be calculated from dissolved oxygen
at the cathode is measured through an electronic circuit and
saturation versus salinity data if internal compensation is not
displayed on a meter. Typically, the anode is constructed of
included in the instrument. Conversion factors for specific
metallic silver or lead and the cathode of gold or platinum.
inorganic salts may be developed experimentally. Broad varia-
Probesaregenerallynotaffectedbyhydraulicpressureandcan
tions in the kinds and concentrations of salts in samples can
be used in the temperature range from 0 to 50°C.
make the use of a membrane probe difficult.
19.1.1 Semipermeable Membranes of Polyethylene or TFE-
18.2.2 Thethalliumprobemeasuresionicactivityinsteadof
fluorocarbon permit satisfactory oxygen diffusion and limit
concentration as do all ion selective electrodes. Gross changes
interference from most materials.
in the concentration of dissolved salts will affect the activity
19.1.2 Accessory Equipment may involve apparatus to
coefficient of the thallous ion and thus shift the span (see
move the sample past the probe and to provide suitable
20.2.1). The thallium probe may be calibrated and operated in
turbulence at the membrane-sample inte
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D888 − 12 D888 − 18
Standard Test Methods for
Dissolved Oxygen in Water
This standard is issued under the fixed designation D888; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Table X2.1 was corrected and the Summary of Changes was added editorially in July 2013.
1. Scope*
1.1 These test methods cover the determination of dissolved oxygen in water. Three test methods are given as follows:
Range, mg/L Sections
Test Method A—Titrimetric Procedure– >1.0 8 to 15
High Level
Test Method A—Titrimetric Procedure–High >1.0 8 – 15
Level
Test Method B—Instrumental Probe Procedure— 0.05 to 20 16 to 25
Electrochemical
Test Method B—Instrumental Probe Procedure—Electrochemical 0.05 to 20 16 – 25
Test Method C—Instrumental Probe Procedure— 0.05 to 20 26 to 29
Luminescence-Based Sensor
Test Method C—Instrumental Probe Procedure—Luminescence-Based 0.05 to 20 26 – 31
Sensor
1.2 The precision of Test Methods A and B was carried out using a saturated sample of reagent water. It is the user’s
responsibility to ensure the validity of the test methods for waters of untested matrices.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For a specific precautionary statement,statements, see 7.1 and Note 17.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
E200 Practice for Preparation, Standardization, and Storage of Standard and Reagent Solutions for Chemical Analysis
3. Terminology
3.1 Definitions—Definitions: For definitions of terms used in these test methods, refer to Terminology D1129.
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
These test methods are under the jurisdiction of ASTM Committee D19 on Water and are the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
Current edition approved March 1, 2012May 1, 2018. Published March 2012May 2018. Originally approved in 1946. Last previous edition approved in 20092012 as
ɛ1
D888 – 09.D888 – 12 . DOI: 10.1520/D0888-12E01.10.1520/D0888-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D888 − 18
3.2 Definitions of Terms Specific to This Standard:
3.2.1 amperometric systems, n—those instrumental probes that involve the generation of an electrical current from which the
final measurement is derived.
3.2.2 instrumental probes, n—devices used to penetrate and examine a system for the purpose of relaying information on its
properties or composition.
3.2.2.1 Discussion—
The term probe is used in these test methods to signify the entire sensor assembly, including electrodes, electrolyte, membrane,
materials of fabrications, and so on.
3.2.3 potentiometric systems, n—those instrumental probes in which an electrical potential is generated and from which the final
measurement is derived.
4. Significance and Use
4.1 Dissolved oxygen is required for the survival and growth of many aquatic organisms, including fish. The concentration of
dissolved oxygen may also be associated with corrosivity and photosynthetic activity. The absence of oxygen may permit anaerobic
decay of organic matter and the production of toxic and undesirable esthetic materials in the water.
5. Purity of Reagents
5.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society. Other
grades may be used if it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the
accuracy of the determination.
5.1.1 Reagent grade chemicals, as defined in Practice E200, shall be used unless otherwise indicated. It is intended that all
reagents conform to this standard.
5.2 Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to Specification
D1193, Type I. Other reagent water types may be used provided it is first ascertained that the water is of sufficiently high purity
to permit its use without adversely affecting the bias and precision of the test method. Type II water was specified at the time of
round robin testing of this test method.
6. Sampling
6.1 Collect the samples in accordance with Practices D1066 and D3370.
6.2 For higher concentration of dissolved oxygen, collect the samples in narrow mouth glass-stoppered bottles of 300-mL
capacity, taking care to prevent entrainment or solution of atmospheric oxygen.
6.3 With water under pressure, connect a tube of inert material to the inlet and extend the tube outlet to the bottom of the sample
bottle. Use stainless steel, Type 304 or 316, or glass tubing with short neoprene connections. Do not use copper tubing, long
sections of neoprene tubing, or other types of polymeric materials. The sample line shall contain a suitable cooling coil if the water
being sampled is above room temperature, in which case cool the sample 16 to 18°C. When a cooling coil is used, the valve for
cooling water adjustment shall be at the inlet to the cooling coil, and the overflow shall be to a point of lower elevation. The valve
for adjusting the flow of sample shall be at the outlet from the cooling coil. The sample flow shall be adjusted to a rate that will
fill the sampling vessel or vessels in 40 to 60 s and flow long enough to provide a minimum of ten changes of water in the sample
vessel. If the sampling line is used intermittently, flush the sample line and cooling coil adequately before using.
6.4 Where samples are collected at varying depths from the surface, a special sample bottle holder or weighted sampler with
a removable air tight cover should be used. This unit may be designed to collect several 250 or 300 mL samples at the same time.
Inlet tubes extending to the bottom of each bottle and the water after passing through the sample bottle or bottles displaces air from
the container. When bubbles stop rising from the sampler, the unit is filled. Water temperature is measured in the excess water in
the sampler.
6.5 For depths greater than 2 m, use a Kemmerer-type sampler. Bleed the sample from the bottom of the sampler through a tube
extending to the bottom of a 250 to 300 mL biological oxygen demand (BOD) bottle. Fill the bottle to overflowing and prevent
turbulence and the formation of bubbles while filling the bottle.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by
the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D888 − 18
7. Preservation of Samples
7.1 Do not delay the determination of dissolved oxygen. Samples for Test Method A may be preserved 4 to 8 h by adding 0.7
mL of concentrated sulfuric acid (sp gr 1.84) and 1.0 mL of sodium azide solution (20 g/L) to the bottle containing the sample
in which dissolved oxygen is to be determined. Biological activity will be inhibited and the dissolved oxygen retained by storing
at the temperature of collection or by water sealing (inverting bottle in water) and maintaining at a temperature of 10 to 20°C.
Complete the determination as soon as possible, using the appropriate procedure for determining the concentration of dissolved
oxygen. (Warning—Sodium azide is highly toxic and multagenic. Follow manufacturerâs instruction for handling and storage.)
TEST METHOD A
TITRIMETRIC PROCEDURE—HIGH LEVEL
8. Scope
8.1 This test method is applicable to waters containing more than 1000 μg/L of dissolved oxygen such as stream and sewage
samples. It is the user’s responsibility to ensure the validity of the test method for waters of untested matrices.
8.2 This test method, with the appropriate agent, is usable with a wide variety of interferences. It is a combination of the Winkler
Method, the Alsterberg (Azide) Procedure, the Rideal-Stewart (permanganate) modification, and the Pomeroy-Kirshman-
Alsterberg modification.
8.3 The precision of the test method was carried out using a saturated sample of reagent water.
8. Scope
8.1 This test method is applicable to waters containing more than 1000 μg/L of dissolved oxygen such as stream and sewage
samples. It is the user’s responsibility to ensure the validity of the test method for waters of untested matrices.
8.2 This test method, with the appropriate agent, is usable with a wide variety of interferences. It is a combination of the Winkler
Method, the Alsterberg (Azide) Procedure, the Rideal-Stewart (permanganate) modification, and the Pomeroy-Kirshman-
Alsterberg modification.
8.3 The precision of the test method was carried out using a saturated sample of reagent water.
9. Interferences
9.1 Nitrite interferences are eliminated by routine use of sodium azide. Ferric iron interferes unless 1 mL of potassium fluoride
solution is used, in which case 100 to 200 mg/L can be tolerated. Ferrous iron interferes, but that interference is eliminated by the
use of potassium permanganate solution. High levels of organic material or dissolved oxygen can be accommodated by use of the
concentrated iodide-azide solution.
10. Apparatus
10.1 Sample Bottles, 250 or 300 mL capacity with tapered ground-glass stoppers. Special bottles with pointed stoppers and
flared mouths are available from supply houses, but regular types (tall or low form) are satisfactory.
10.2 Pipettes, 10-mL capacity, graduated in 0.1-mL divisions for adding all reagents except sulfuric acid. These pipettes should
have elongated tips of approximately 10 mm for adding reagents well below the surface in the sample bottle. Only the sulfuric acid
used in the final step is allowed to run down the neck of the bottle into the sample.
11. Reagents
11.1 Alkaline Iodide Solutions:
11.1.1 Alkaline Iodide Solution—Dissolve 500 g of sodium hydroxide or 700 g of potassium hydroxide and 135 g of sodium
iodide or 150 g of potassium iodide (KI) in water and dilute to 1 L. Chemically equivalent potassium and sodium salts may be
used interchangeably. The solution should not give a color with starch indicator when diluted and acidified. Store the solution in
a dark rubber-stoppered bottle. This solution may be used if nitrite is known to be absent and must be used if adjustments are made
for ferrous ion interference.
11.1.2 Alkaline Iodide-Sodium Azide Solution I—This solution may be used in all of these submethods except when adjustment
is made for ferrous ion. Dissolve 500 g of sodium hydroxide or 700 g of potassium hydroxide and 135 g of sodium iodide or 150
g of potassium iodide in water and dilute to 950 mL. To the cooled solution add 10 g of sodium azide dissolved in 40 mL of water.
Add the NaN solution slowly with constant stirring. Chemically equivalent potassium and sodium salts may be used
interchangeably. The solution should not give a color with starch indicator solution when diluted and acidified. Store the solution
in a dark rubber-stoppered bottle. (See 7.1.)
11.1.3 Alkaline Iodide-Sodium Azide Solution II—This solution is useful when high concentrations of organic matter are found
or when the dissolved oxygen concentration exceeds 15 mg/L. Dissolve 400 g of sodium hydroxide in 500 mL of freshly boiled
and cooled water. Cool the water slightly and dissolve 900 g of sodium iodide. Dissolve 10 g of sodium azide in 40 mL of water.
Slowly add, with stirring, the azide solution to the alkaline iodide solution, bringing the total volume to 1 L. (See 7.1.)
D888 − 18
11.2 Manganous Sulfate Solution—Dissolve 364 g of manganous sulfate in water, filter, and dilute to 1 L. No more than a trace
of iodine should be liberated when the solution is added to an acidified potassium iodide solution.
11.3 Potassium Biiodate Solution (0.025 N)—Dissolve 0.8125 g of potassium biiodate in water and dilute to 1 L in a volumetric
flask.
NOTE 1—If the bottle technique is used, dissolve 1.2188 g of biiodate in water and dilute to 1 L to make 0.0375 N.
11.4 Phenylarsine Oxide Solution (0.025 N)—Dissolve 2.6005 g of phenylarsine oxide in 110 mL of NaOH solution (12 g/L).
Add 800 mL of water to the solution and bring to a pH of 9.0 by adding HCl (1 + 1). This should require about 2 mL of HCl.
Continue acidification with HCl (1 + 1) until a pH of 6 to 7 is reached, as indicated by a glass-electrode system. Dilute to 1 L. Add
1 mL of chloroform for preservation. Standardize against potassium biiodate solution.
NOTE 2—Phenylarsine oxide is more stable than sodium thiosulfate. However, sodium thiosulfate may be used. The analyst should specify which titrant
is used. For a stock solution (0.1 N), dissolve 24.82 g of Na S O ·5H O in boiled and cooled water and dilute to 1 L. Preserve by adding 5 mL of
2 2 3 2
chloroform. For a dilute standard titrating solution (0.005 N) transfer 25.00 mL of 0.1 N Na S O to a 500-mL volumetric flask. Dilute to the mark with
2 2 3
water and mix completely. Do not prepare more than 12 to 15 h before use.
NOTE 3—If the full bottle technique is used, 3.9007 g must be used to make 0.0375 N.
NOTE 4—If sodium thiosulfate is used, prepare and preserve a 0.1 N solution as described in Note 1. Determine the exact normality by titration against
0.025 N potassium biiodate solution. Dilute the appropriate volume (nominally 250 mL) of standardized 0.1 N Na S O solution to 1 L. One millilitre
2 2 3
of 0.025 N thiosulfate solution is equivalent to 0.2 mg of oxygen. If the full bottle technique is followed, use 37.5 mL of sodium thiosulfate solution and
standardize to 0.0375 N.
11.5 Starch Solution—Make a paste of 6 g of arrowroot starch or soluble iodometric starch with cold water. Pour the paste into
1 L of boiling water. Then add 20 g of potassium hydroxide, mix thoroughly, and allow to stand for 2 h. Add 6 mL of glacial acetic
acid (99.5 %). Mix thoroughly and then add sufficient HCl (sp gr 1.19) to adjust the pH value of the solution to 4.0. Store in a
glass-stoppered bottle. Starch solution prepared in this manner will remain chemically stable for one year.
NOTE 5—Powdered starches such as thyodene have been found adequate. Some commercial laundry starches have also been found to be usable.
NOTE 6—If the indicator is not prepared as specified or a proprietary starch indicator preparation is used, the report of analysis shall state this deviation.
11.6 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid. One millilitre neutralizes about 3 mL of the alkaline iodide reagent.
NOTE 7—Sulfamic acid (3 g) may be substituted.
11.7 Potassium Fluoride Solution (400 g/L)—Dissolve 40 g of potassium fluoride in water and dilute to 100 mL. This solution
is used in the procedure for eliminating ferric ion interference. Store this solution in a plastic bottle.
11.8 Potassium Oxalate Solution (20 g/L)—Dissolve 2 g of potassium oxalate in 100 mL of water. One millilitre of this solution
will reduce 1.1 mL of the KMnO solution. This solution is used in the procedure for eliminating ferrous ion interference.
11.9 Potassium Permanganate Solution (6.3 g/L)—Dissolve 6.3 g of potassium permanganate in water and dilute to 1 L. With
very high ferrous iron concentrations, solution of KMnO should be stronger so that 1 mL will satisfy the demand. This solution
is used in the procedure for eliminating ferrous ion interference.
12. Procedure
12.1 Elimination of Ferrous Ion Interference, If Necessary:
12.1.1 Add to the sample (collected as in 6.2) 0.70 mL of H SO , followed by 1.0 mL of KMnO solution. Where high iron
2 4 4
is present, also add 1.0 mL of KF solution. Stopper and mix by inversion. The acid should be added with a 1-mL pipette graduated
in 0.1-mL divisions. Add sufficient KMnO solution to maintain a violet tinge for 5 min. If the color does not persist for 5 min,
add more KMnO solution, but avoid excess. In those cases where more than 5 mL of KMnO solution is required, a stronger
4 4
solution of this reagent may be used to avoid dilution of the sample.
12.1.2 After 5 min, completely destroy the permanganate color by adding 0.5 to 1.0 mL of K C O solution. Mix the sample
2 2 4
well, and allow it to stand in the dark. Low results are caused by excess oxalate so it is essential to add only sufficient oxalate to
completely decolorize the permanganate without having an excess of more than 0.5 mL. Complete decolorization should be
obtained in 2 to 10 min. If the sample cannot be decolorized without a large excess of oxalate, the dissolved oxygen results will
be of doubtful value.
12.2 Add 2.0 mL of MnSO solution to the sample as collected in a sample bottle, followed by 2.0 mL of alkaline iodide-sodium
azide solution well below the surface of the liquid (see Note 8 and Note 9). Be sure the solution temperature is below 30°C to
prevent loss due to volatility of iodine. Carefully replace the stopper to exclude air bubbles and mix by inverting the bottle several
times. Repeat the mixing a second time after the floc has settled, leaving a clear supernatant solution. Water high in chloride
requires a 10-min contact period with the precipitate. When the floc has settled, leaving at least 100 mL of clear supernatant
solution, remove the stopper, and add 2.0 mL of H SO , allowing the acid to run down the neck of the bottle. Restopper and mix
2 4
by inversion until the iodine is uniformly distributed throughout the bottle. Titrate without delay 203 mL of original sample. A
correction is necessary for the 4 mL of reagents added (2 mL of MnSO solution and 2 mL of alkaline iodide-sodium azide solution:
200 × [300 ⁄(300 − 4)] = 203 mL (see Note 10)).
D888 − 18
NOTE 8—Take care to use the correct alkaline iodide solution (11.1.1) if no nitrite is present or ferrous ion was oxidized, (11.1.2) for normal use, or
(11.1.3) if there is a high organic or dissolved oxygen concentration.
NOTE 9—Two millilitres of the alkaline iodide-sodium azide solution are used to ensure better contact of the iodide-azide solution and sample with
less agitation. With 250-mL bottles, 1 mL of the iodide-azide solution may be used if desired. In this procedure, as in the succeeding ones, all reagents
except the H SO are added well below the surface of the liquid.
2 4
NOTE 10—In the case where ferrous ion interference has been eliminated, a total of 6.7 mL of reagents were added (0.7 mL of acid, 1 mL of KMnO
solution, 2 mL of MnSO solution, and 3 mL of alkaline iodide solution). The volume of sample for titration is 203 mL. A slight error occurs due to the
dissolved oxygen of the KMnO solution, but rather than complicate the correction further, this error is ignored.
12.3 Rapidly titrate the 203 mL of sample with 0.025 N titrating solution to a pale, straw yellow color. Add 1 to 2 mL of starch
indicator. Continue the titration to the disappearance of the blue color.
NOTE 11—If the full bottle technique is used, transfer the entire contents of the bottle, 300 6 3 mL, to a 500-mL Erlenmeyer flask and titrate with
0.0375 N titrating solution.
NOTE 12—At the correct end point, one drop of 0.025 N KH(IO ) solution will cause the return of the blue color. If the end point is overrun, continue
3 2
adding 0.025 N KH(IO ) solution until it reappears, noting the volume required. Subtract this value, minus the last drop of KH(IO ) (0.04 mL) from
3 2 3 2
the volume of 0.025 N titrating solution used. Disregard the late reappearance of the blue color, which may be due to the catalytic effect of organic material
or traces of uncomplexed metal salts.
13. Calculation
13.1 Calculate the dissolved oxygen content of the sample as follows:
T 30.2
Dissolved oxygen, mg/L5 31000 (1)
where:
T = 0.025 N titrating solution required for titration of the sample, mL.
13.2 Use Eq 2 to convert to a standard temperature and pressure measurement.
A
Dissolved oxygen, mg/L5 (2)
0.698
where:
A = oxygen at 0°C and 760 mm Hg, mL.
NOTE 13—Each millilitre of 0.0375 N titrant is equivalent to 1 mg/L O when the full bottle technique is used.
NOTE 14—If the percentage of saturation at 760-mm atmospheric pressure is desired, the dissolved oxygen found is compared with solubility data from
standard solubility tables, making corrections for barometric pressure and the aqueous vapor pressure, when necessary. See Appendix X1.
14. Precision and Bias
14.1 The precision of the test method was determined by six operators in three laboratories, running three duplicates each (not
six laboratories as required by Practice D2777) using a saturated sample of reagent water. The mean concentration was 9.0 mg/L,
and the pooled single operator precision in these samples was 0.052 mg/L.
14.2 Precision and bias for this test method conforms to Practice D2777 – 77, which was in place at the time of collaborative
testing. Under the allowances made in 1.4 of Practice D2777 – 08, – 13, these precision and bias data do meet existing
requirements for interlaboratory studies of Committee D19 test methods.
15. Quality Control (QC)
15.1 In order to be certain To ensure that analytical values obtained using these test methods are valid and accurate within the
confidence limits of the test, the following QC procedures must be followed when analyzing dissolved oxygen.
15.2 Calibration and Calibration Verification:
15.2.1 Standardize the titrating solution against the potassium biiodate solution.
15.2.2 Verify titrating solution by analyzing a sample with a known amount of the dissolved oxygen, if possible. The amount
of the sample should fall within 615 % of the known concentration.
15.2.3 If standardization cannot be verified, restandardize the solution.
15.3 Initial Demonstration of Laboratory Capability:
15.3.1 If a laboratory has not performed the test before, or if there has been a major change in the measurement system, for
example, new analyst, new instrument, and so forth, a precision and bias study must be performed to demonstrate laboratory
capability.
Carpenter, J. H., “New Measurement of Oxygen Solubility in Pure and Natural Water,” Limnology and Oceanography, Vol 11, No. 2, April 1966, pp. 264–277.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D19-1070. Contact ASTM Customer
Service at [e-mail].
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15.3.2 Analyze seven replicates of the same solution. Each replicate must be taken through the complete analytical test method
including any sample preservation and pretreatment steps.
15.3.3 Calculate the mean and standard deviation of the seven values and compare to the acceptable ranges of bias in 14.1. This
study should be repeated until the recoveries are within the limits given in 14.1. If an amount other than the recommended amount
is used, refer to Practice D5847 for information on applying the F test and t test in evaluating the acceptability of the mean and
standard deviation.
15.4 Laboratory Control Sample (LCS):
15.4.1 Air-saturated reference water samples may be used for laboratory control samples. The value obtained must fall within
the control limits established by the laboratory.
15.5 Method Blank:
15.5.1 Analyze a reagent water test blank with each batch. The amount of dissolved oxygen found in the blank should be less
than the analytical reporting limit. If the amount of dissolved oxygen is found above this level, analysis of samples is halted until
the contamination is eliminated, and a blank shows no contamination at or above this level, or the results must be qualified with
an indication that they do not fall within the performance criteria of the test method.
15.6 Matrix Spike (MS):
15.6.1 Dissolved oxygen is not an analyte that can be feasibly spiked into samples.
15.7 Duplicate:
15.7.1 To check the precision of sample analyses, analyze a sample in duplicate with each batch. The value obtained must fall
within the control limits established by the laboratory.
15.7.2 Calculate the standard deviation of the duplicate values and compare to the precision determined by the laboratory or
in the collaborative study using an F test. Refer to 6.4.4 of Practice D5847 for information on applying the F test.
15.7.3 If the result exceeds the precision limit, the batch must be reanalyzed or the results must be qualified with an indication
that they do not fall within the performance criteria of the test method.
15.8 Independent Reference Material (IRM):
15.8.1 Independent reference water samples may be obtained from commercial sources. The value obtained from these samples
must fall within the control limits established by the laboratory.
TEST METHOD B
INSTRUMENTAL PROBE PROCEDURE—ELECTROCHEMICAL
16. Scope
16.1 This test method is applicable to waters containing dissolved oxygen in the range from 50 to 20 000 μg/L. It is the user’s
responsibility to ensure the validity of this test method for waters of untested matrices.
16.2 This test method describes procedures that utilize electrochemical probes for the determination of dissolved oxygen in
fresh water and in brackish and marine waters that may contain dissolved or suspended solids. Samples can be analyzed in situ
in bodies of water or in streams, or samples can be collected and analyzed subsequent to collection. The electrochemical probe
method is especially useful in the monitoring of water systems in which it is desired to obtain a continuous record of the dissolved
oxygen content.
16.2.1 This test method is recommended for measuring dissolved oxygen in waters containing materials that interfere with the
chemical methods, such as sulfite, thiosulfate, polythionate, mercaptans, oxidizing metal ions, hypochlorite, and organic substances
readily hydrolyzable in alkaline solutions.
16.3 Electrochemical dissolved oxygen probes are practical for the continuous monitoring of dissolved oxygen content in
natural waters, process streams, biological processes, and so on, when the probe output is conditioned by a suitably stable
electronic circuit and recorded. The probe must be standardized before use on samples free of interfering materials, preferably with
the azide modification of Test Method A.
16. Scope
16.1 This test method is applicable to waters containing dissolved oxygen in the range from 50 to 20 000 μg/L. It is the user’s
responsibility to ensure the validity of this test method for waters of untested matrices.
16.2 This test method describes procedures that utilize electrochemical probes for the determination of dissolved oxygen in
fresh water and in brackish and marine waters that may contain dissolved or suspended solids. Samples can be analyzed in situ
in bodies of water or in streams, or samples can be collected and analyzed subsequent to collection. The electrochemical probe
method is especially useful in the monitoring of water systems in which it is desired to obtain a continuous record of the dissolved
oxygen content.
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16.2.1 This test method is recommended for measuring dissolved oxygen in waters containing materials that interfere with the
chemical methods, such as sulfite, thiosulfate, polythionate, mercaptans, oxidizing metal ions, hypochlorite, and organic substances
readily hydrolyzable in alkaline solutions.
16.3 Electrochemical dissolved oxygen probes are practical for the continuous monitoring of dissolved oxygen content in
natural waters, process streams, biological processes, and so on, when the probe output is conditioned by a suitably stable
electronic circuit and recorded. The probe must be standardized before use on samples free of interfering materials, preferably with
the azide modification of Test Method A.
17. Summary of Test Method
17.1 The most common instrumental probes for determination of oxygen dissolved in water are dependent upon electrochemical
reactions. Under steady-state conditions, the current or potential can be correlated with dissolved oxygen concentrations.
NOTE 15—Steady-state conditions necessitate the probe being in thermal equilibrium with the solution, this typically taking 20 min for nonlaboratory
conditions.
17.1.1 Probes that employ membranes normally involve metals of different nobility immersed in an electrolyte that is retained
by the membrane. The metal of highest nobility (the cathode) is positioned at the membrane. When a suitable potential exists
between the two metals, reduction of oxygen to hydroxide ion occurs at the cathode surface. An electrical current is developed that
is directly proportional to the rate of arrival of oxygen molecules at the cathode.
17.1.2 The thallium probe, which does not utilize a membrane, exposes a thallium electrode to the water sample. Reaction of
oxygen with the thallium establishes a potential between the thallium electrode and a reference electrode. The potential is related
logarithmically to dissolved oxygen concentration. The cell output decreases (theoretically 59 mV/decade at 25°C) with increased
oxygen concentration.
NOTE 16—The thallium probe has utility in waste treatment monitoring systems; it has limited application under conditions of high dissolved oxygen
(>8 mg/L) and low temperature (<10°C).
17.1.3 The electronic readout meter for the output from dissolved oxygen probes is normally calibrated in convenient scales (0
to 10, 0 to 15, or 0 to 20 mg/L) with a sensitivity of approximately 0.05 mg/L. More sensitive dissolved oxygen ranges are practical
through amplification in the electronic readout (including μg/L readings in boiler feed waters).
17.2 Interfacial dynamics at the probe-sample interface are a factor in probe response. Turbulence should be constant or above
some minimum level as recommended by the instrument manufacturer.
17.3 Response rates of dissolved oxygen probes are relatively rapid, often as fast as 99 % in 15 s. Probe outputs may be recorded
for continual monitoring or utilized for process control (see Note 15).
18. Interferences
18.1 Dissolved organic materials normally encountered in water are not known to interfere in the output from dissolved oxygen
probes.
18.2 Dissolved inorganic salts are a factor in the calibration of dissolved oxygen probe.
18.2.1 Solubility of oxygen in water at a given oxygen partial pressure changes with the kind and concentration of dissolved
inorganic salts. Conversion factors for seawater and brackish waters may be calculated from dissolved oxygen saturation versus
salinity data if internal compensation is not included in the instrument. Conversion factors for specific inorganic salts may be
developed experimentally. Broad variations in the kinds and concentrations of salts in samples can make the use of a membrane
probe difficult.
18.2.2 The thallium probe measures ionic activity instead of concentration as do all ion selective electrodes. Gross changes in
the concentration of dissolved salts will affect the activity coefficient of the thallous ion and thus shift the span (see 20.2.1). The
thallium probe may be calibrated and operated in water of any conductivity above 100 μS, but a ten-fold change in conductivity
will produce an error of approximately 20 %. Since the thallium requires a conducting path through the sample to the reference
electrode, the response will become sluggish at very low conductivity. It is therefore desirable to calibrate the sensor in solutions
having a conductivity greater than 100 μS.
18.3 Reactive compounds can interfere with the output or the performance of dissolved oxygen probes.
18.3.1 Membrane probes are sensitive to reactive gases that may pass through the membrane. Chlorine will depolarize the
cathode and cause a high probe output. Long-term exposure to chlorine can coat the anode with the chloride of the anode metal
and may eventually desensitize the probe. Hydrogen sulfide will interfere with membrane probes if the applied potential is greater
than the half-wave potential of the sulfide ion. If the applied potential is less than the half-wave potential, an interfering reaction
will not occur, but coating of the anode metal can occur.
D’Aoust, B. G., Clark, M. J. R., “Analysis of Supersaturated Air in Natural Waters and Reservoirs,” Transactions of the American Fisheries Society, Vol 109, 1980, pp.
708–724.
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18.3.2 The thallium probe is affected by interference from soluble sulfur compounds, such as hydrogen sulfide or mercaptans.
Ten milligrams of hydrogen sulfide per litre of water will produce a negative error corresponding to approximately 1 mg/L of
dissolved oxygen. Free halogens also will interfere with the thallium probe if present in appreciable concentrations, such as above
2 mg of chlorine per litre of water.
18.4 At dissolved oxygen concentrations below 2 mg/L, pH variation below 4 and above 10 interfere with the performance of
the thallium probe (approximately 60.05 mg/L dissolved oxygen per pH unit). The performance of membrane probes is not
affected by pH changes.
18.5 Dissolved oxygen probes are temperature sensitive and temperature compensation is normally provided by the
manufacturer. The thallium probe has a temperature coefficient of 1.0 mV/°C, membrane probes have a temperature coefficient of
4 to 6 % ⁄°C dependent upon the membrane employed.
18.6 Insoluble organic or inorganic materials that can coat the surface of dissolved oxygen probes will affect the performance
of either the thallium or membrane probes.
19. Apparatus
19.1 Amperometric Probes—Oxygen-sensitive probes of the amperometric type are normally composed of two solid metal
electrodes of different nobility in contact with a supporting electrolyte that is separated from the test solution by a selective
membrane. The current generated by the reduction of oxygen at the cathode is measured through an electronic circuit and displayed
on a meter. Typically, the anode is constructed of metallic silver or lead and the cathode of gold or platinum. Probes are generally
not affected by hydraulic pressure and can be used in the temperature range from 0 to 50°C.
19.1.1 Semipermeable Membranes of Polyethylene or TFE-fluorocarbon permit satisfactory oxygen diffusion and limit
interference from most materials.
19.1.2 Accessory Equipment may involve apparatus to move the sample past the probe and to provide suitable turbulence at the
membrane-sample interface.
19.2 Potentiometric Probes—The commonly used potentiometric probe employs a thallium-measuring electrode and a suitable
reference half cell such as a saturated calomel. At 25°C and 0.1 mg/L of dissolved oxygen, the cell establishes a negative potential
of approximately 817 mV. The potential decreases logarithmically in absolute value with increased dissolved oxygen concentration
(theoretically, 59 mV/decade change in dissolved oxygen concentration) to approximately 688 mV at 15 mg/L of dissolved oxygen.
An external millivoltage source that opposes the output of the electrometer is used to adjust the net readout of output to the desired
range.
NOTE 17—Thallium and its salts are toxic. Avoid contact with the skin.
20. Apparatus Standardization
20.1 Under equilibrium conditions, the partial pressure of oxygen in air-saturated water is equal to that of the oxygen in the
water-saturated air. Consequently, a probe may be calibrated in air as well as water. Consider carefully the manufacturer’s
recommended procedure. If it is necessary to zero the instrument, immerse the probe in water containing 1 g of sodium sulfite and
two drops of saturated cobalt chloride solution (as deoxygenation catalyst) per litre of water and adjust the instrument to read zero.
If a water-saturated air calibration is necessary, follow the manufacturer’s directions for its preparation.
20.2 To calibrate the probe in water, carefully obtain approximately 1 L of the type of water to be tested and saturate it with
oxygen from the atmosphere by passing clean air through it. Carefully draw three replicate samples from the well-mixed sample
and immediately determine the dissolved oxygen concentration by Test Method A in duplicate. In the third replicate sample,
immerse the probe and provide for suitable turbulence in the sample. Standardize the probe by adjusting the meter reading to the
dissolved oxygen value as determined by the chemical procedure. If substances that interfere with the chemical method are present
in the natural water or wastewater sample, standardize the probe using reagent water or a synthetic sample as indicated below.
20.2.1 Fresh Water Samples (less than 1000 mg/L of dissolved salts)—If chemical interferences are absent, use a test sample
as indicated above. If interferences are present, use reagent water for membrane probes. With thallium probes, the greatest accuracy
can be obtained from calibrating in a sample of the water to be tested or a synthetic sample similar to the test sample.
20.2.2 Salt Water Samples and Membrane Probes (greater than 1000 mg/L of dissolved salts)—Use a sample of clean water
having the same salt content as the test material. If a sample free from substances that interfere with the azide method is not
available, prepare a synthetic standardization sample by adding the same salts contained in the sample until the two solutions have
the same electrical conductance within 5 %. High concentrations of dissolved salts are not a problem with the thallium probe.
20.3 Temperature Coeffıcient—Systems are available with automatic temperature compensation that permit direct measurements
in milligrams per litre of dissolved oxygen. The temperature compensation of membrane probes corrects for changes in membrane
characteristics including boundary-layer effects at the membrane-water interface and the changes in solubility of oxygen in water.
The temperature compensation of thallium probes corrects for the changes characteristic of oxidation/reduction systems (see Note
15). It is necessary that the probe is in thermal equilibrium with the solution to be measured for satisfactory temperature correction.
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20.3.1 For those instrumental systems using membrane probes that are not temperature-compensated, the following procedure
is recommended to obtain the temperature coefficient. Measure the oxygen content in water samples for five temperatures over a
610°C range greater and less than the expected sample temperature. By a least-squares procedure, or graphically in a semilog plot
of Y versus T, calculate the slope and intercept constant as follows:
Log y 5 B/T1A (3)
where:
y = scale factor, milligrams of dissolved oxygen per litre per microampere of electrode current,
B = slope constant,
T = temperature, °C, and
A = intercept constant.
This relationship is linear on a semilog plot only over a range of 610°C. Over larger ranges an equation of higher degree is
necessary to reflect the curvature of the relationship.
20.3.2 If the thallium probe is utilized in a circuit without temperature compensation, the observed output in millivolts must be
corrected for the temperature sensitivity of the measuring cell that has a temperature coefficient of 1.0 mV/°C. The measuring cell’s
output will increase (apparent dissolved oxygen concentration decrease) with an increase in temperature,
MV 5 MV 2 1.0 ~T 2 T ! (4)
R 0 o R
where:
MV = millivolts of output at reference temperature,
R
MV = millivolts of output observed,
T = reference temperature, °C, and
R
T = temperature at the observed output, °C.
o
20.4 Correction for Content of Dissolved Salts—If the concentration of salts is above 1000 mg/L, it will be necessary to correct
for the effect of the salts in the relationship between oxygen partial pressure and concentration and also for the activity of thallium
ion. For any given salt, a series of experimental data should be obtained in which solutions are prepared by dissolving varying
weights of the salt in reagent water in the range of interest. The solutions plus a reagent water control are aerated at constant
temperature until oxygen saturation is achieved. Determine the oxygen concentration of each solution by the chemical method and,
at the same time, obtain probe readings. Determine the ratio A for each solution as follows:
A 5 O/R (5)
where:
O = actual dissolved oxygen concentration, mg/L, as determined by Test Method A, and
R = reading of the probe meter.
For the reagent water control to which the probe is calibrated, the value of A is 1.0. Prepare a plot with salt concentration as
abscissa and the ratio A as ordinate. Use the developed curve for calculation of the dissolved oxygen content of salt waters.
21. Sampling
21.1 Bottle Samples—Collect a bottle sample by the procedure described in PracticePractices D1066 or Practices D3370.
Collect the samples in 300-mL BOD bottles or other suitable glass-stoppered bottles, preventing entrainment or solution of
atmospheric oxygen. If analysis is delayed beyond 15 min, cool the sample below 5°C and hold at this temperature until analyzed.
Make the dissolved oxygen determination without further temperature adjustment using the appropriate temperature coefficient. It
will be necessary to have the probe at the temperature of the sample or otherwise compensate for instability due to heat flow from
probe to sample.
21.2 In Situ Samples—An effective use of the instrumental probes is for the direct, in situ determination of dissolved oxygen.
By this means, sample handling problems are avoided, and data may be obtained quickly at various locations in a body of water
without concern for the change in oxygen during storage or handling.
22. Procedure
22.1 Consider carefully the manufacturer’s recommendations on the use of equipment to obtain satisfactory operation.
22.2 Provide for suitable turbulent flow past the membrane of membrane probes or past the thallium probe. This may, under
some circumstances, be achieved adequately in flowing streams. However, in large bodies of water, it may be necessary to employ
mechanical stirring or pumping of water past the probe. For accurate results, it is important that comparable degrees of turbulence
be employed both for calibration and utilization.
22.3 If the probe is not automatically compensated for temperature changes, record the temperature of the water at the sample
probe at the time of dissolved oxygen measurement. To avoid heat-flow effects, it is important that temperature equilibrium be
established between sample and probe.
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