ASTM D5462-21

Standard Test Method for On-Line Measurement of Low-Level Dissolved Oxygen in Water

SIGNIFICANCE AND USE
5.1 DO may be either a corrosive or passivating agent in boiler/steam cycles and is therefore controlled to specific concentrations that are low relative to environmental and wastewater treatment samples. Out-of-specification DO concentrations may cause corrosion in boiler systems, which leads to corrosion fatigue and corrosion products — all detrimental to the life and efficient operation of a steam generator. The efficiency of DO removal from boiler feedwater by mechanical or chemical means, or both, may be monitored by continuously measuring the DO concentration before and after the removal process with on-line instrumentation. DO measurement is also a check for air leakage into the boiler water cycle.  
5.2 Feedwater chemistry guidelines for high-pressure boilers generally require specific feedwater DO concentrations: 5 μg/L or less for reducing all volatile treatment [AVT(R)]; 5–10 μg/L for oxidizing all volatile treatment [AVT(O)]; 50–200 μg/L for oxygenated treatment [OT] (3).  
5.3 In microelectronics production, DO can be detrimental in some manufacturing processes, for example, causing undesirable oxidation on silicon wafers.
SCOPE
1.1 This test method covers the on-line determination of dissolved oxygen (DO) in water samples primarily in ranges from 0 to 500 μg/L (ppb), although higher ranges may be used for calibration. On-line instrumentation is used for continuous measurements of DO in samples that are brought through sample lines and conditioned from high-temperature and high-pressure sources when necessary.  
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.3 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 specific hazards statements, see 6.5.  
1.4 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: 31-May-2021
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.03 - Sampling Water and Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of 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 D3864-06 - Standard Guide for Continual On-Line Monitoring Systems for Water Analysis
• Effective Date: 01-Jul-2006

Overview

ASTM D5462-21 is the internationally recognized standard test method for the on-line measurement of low-level dissolved oxygen (DO) in water. Developed by ASTM International, this standard is crucial for industries requiring continuous, accurate monitoring of dissolved oxygen concentrations, particularly in high-purity water applications such as power generation and microelectronics manufacturing. The method is applicable to water samples typically ranging from 0 to 500 µg/L (ppb) of DO but allows for higher ranges during calibration. Measurement is performed via on-line instrumentation capable of delivering real-time data, improving process control, system reliability, and water quality management.

Key Topics

• DO Measurement Principles: Utilizes electrochemical probes-either diffusion-type (galvanic or polarographic) or equilibrium-type-to detect dissolved oxygen using gas-permeable membranes and precise temperature compensation for accurate readings.
• Importance in Power Generation: Low-level DO measurement is essential in boiler and steam cycles to prevent corrosion, corrosion fatigue, and the accumulation of corrosion products, which reduce the service life and operational efficiency of steam generators.
• Microelectronics Manufacturing: Stringent DO control prevents undesirable oxidation, particularly on sensitive materials like silicon wafers.
• Continuous Monitoring: On-line, real-time DO measurement detects process upsets, verifies oxygen removal efficiency, and identifies air ingress, ensuring compliance with industry specifications.
• Calibration and Maintenance: Provides guidance on instrument and probe calibration, periodic maintenance, and quality control to guarantee accurate, repeatable results.
• Sampling Best Practices: Emphasizes selecting appropriate sample line materials (e.g., stainless steel, PVDF, Nylon), maintaining flow rates, and preventing atmospheric contamination.

Applications

ASTM D5462-21 is widely applied in industries requiring precise, continuous measurement of low-level dissolved oxygen:

• Power Plants: Monitoring DO in boiler feedwater and throughout the steam cycle to ensure concentration levels suitable for reducing [AVT(R)], oxidizing [AVT(O)], and oxygenated [OT] treatments.
• Industrial Process Water: Maintaining water chemistry control in systems where DO impacts corrosion rates or process effectiveness.
• Microelectronics: Achieving ultra-pure water conditions to prevent device defects caused by unintended oxidation during manufacturing.
• Quality Assurance: Ensuring DO levels remain within specification for regulatory compliance and system efficiency.
• Leak Detection: Identifying air ingress or system breaches by detecting abnormal increases in DO concentrations.

Practical Benefits

• Enhanced Corrosion Protection: Reduces maintenance costs and extends equipment lifespan by identifying and controlling corrosive oxygen levels.
• Real-Time Process Optimization: Immediate feedback for adjustments in water treatment processes, ensuring efficient chemical usage and system operation.
• Data-Driven Decision Making: Continuous monitoring provides traceable records for operational audits and regulatory reporting.

Related Standards

For effective implementation of ASTM D5462-21, consider its relationship with related ASTM water analysis standards:

• ASTM D1066 - Practice for Sampling Steam
• ASTM D3370 - Practices for Sampling Water from Flowing Process Streams
• ASTM D3864 - Guide for On-Line Monitoring Systems for Water Analysis
• 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 D1129 - Terminology Relating to Water

These referenced standards support sampling, analysis, terminology, and calibration, ensuring more reliable and reproducible low-level dissolved oxygen measurements in water.

---

Keywords: ASTM D5462-21, dissolved oxygen, on-line measurement, water analysis, boiler feedwater, corrosion prevention, power generation water, microelectronics water purity, continuous DO monitoring, water quality standard

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: D5462 − 21
Standard Test Method for
On-Line Measurement of Low-Level Dissolved Oxygen in
Water
This standard is issued under the fixed designation D5462; 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.
1. Scope D3370 Practices for Sampling Water from Flowing Process
Streams
1.1 This test method covers the on-line determination of
D3864 Guide for On-Line Monitoring Systems for Water
dissolved oxygen (DO) in water samples primarily in ranges
Analysis
from 0 to 500 µg/L(ppb), although higher ranges may be used
for calibration. On-line instrumentation is used for continuous
3. Terminology
measurements of DO in samples that are brought through
sample lines and conditioned from high-temperature and high-
3.1 Definitions:
pressure sources when necessary.
3.1.1 For definitions of terms used in this standard, refer to
Terminology D1129.
1.2 The values stated in SI units are to be regarded as
standard. The values given in parentheses after SI units are
3.2 Definitions of Terms Specific to This Standard:
provided for information only and are not considered standard.
3.2.1 diffusion-type probes, n—galvanic or polarographic
1.3 This standard does not purport to address all of the sensorsthatdependonthecontinuousinfluxofoxygenthrough
safety concerns, if any, associated with its use. It is the the membrane to develop the electrical signal.
responsibility of the user of this standard to establish appro-
3.2.2 equilibrium-type probes, n—modified polarographic
priate safety, health, and environmental practices and deter-
sensing probes that have a negligible influx of oxygen through
mine the applicability of regulatory limitations prior to use.
the membrane except during changes of sample DO concen-
For specific hazards statements, see 6.5.
tration.
1.4 This international standard was developed in accor-
3.2.2.1 Discussion—Oxygen consumption and regeneration
dance with internationally recognized principles on standard-
balance each other within the probes under stable conditions,
ization established in the Decision on Principles for the
and the net flux through the membrane is insignificant.
Development of International Standards, Guides and Recom-
3.2.3 galvanic systems, n—sensing probes and measuring
mendations issued by the World Trade Organization Technical
instruments that develop an electrical current from two elec-
Barriers to Trade (TBT) Committee.
trodes inside the probe from which the final measurement is
derived.
2. Referenced Documents
3.2.4 partialpressure(ofoxygen),n—thevolumefractionof
2.1 ASTM Standards:
oxygen multiplied by the total pressure.
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water 3.2.4.1 Discussion—The partial pressure of oxygen is the
actual parameter detected by DO probes, whether in air or
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of dissolved in water.
Applicable Test Methods of Committee D19 on Water
3.2.5 polarographic systems, n—sensing probes and mea-
suring instruments that include circuitry to control the operat-
ing voltage of the system, usually using a third (reference)
This test method is under the jurisdiction of ASTM Committee D19 on Water
electrode in the probe.
and is the direct responsibility of Subcommittee D19.03 on Sampling Water and
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use,
On-Line Water Analysis, and Surveillance of Water.
4. Summary of Test Method
Current edition approved June 1, 2021. Published June 2021. Originally
4.1 Dissolved oxygen is measured by means of an electro-
approved in 1993. Last previous edition approved in 2013 as D5462 – 13. DOI:
10.1520/D5462-21.
chemical cell separated from the sample by a gas-permeable
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
membrane. Behind the membrane and inside the probe, elec-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
trodes immersed in an electrolyte develop an electrical current
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. proportional to the oxygen partial pressure of the sample.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5462 − 21
4.2 The partial pressure signal is temperature compensated 6. Interferences
automatically to account for variations with temperature of the
6.1 The leakage of atmospheric air into samples is some-
following: oxygen solubility in water; electrochemical cell
timesdifficulttoavoidanddetect.Althoughsamplelinefittings
output; and, when necessary, diffusion rate of oxygen through
and connections to flow chambers may be water tight, it is still
the membrane. This yields a direct readout in concentration of
possible for air to diffuse through the water film of a joint to
µg/L (ppb) or mg/L (ppm).
contaminate a low-µg/L sample. Sample flow through fittings,
valves and rotometers can create a venturi effect, which draw
4.3 Diffusion-type probes rely on a continuous diffusion of
ambient air into the sample. Section 9 provides further details
oxygen through the membrane. Immediately inside the
on this non-obvious interference.
membrane, oxygen is reduced at the noble metal cathode,
usually platinum or gold. An electrical current is developed
6.2 Diffusion-type probes consume oxygen and will deplete
that is directly proportional to the arrival rate of oxygen
it from the sample in immediate contact with the membrane
molecules at the cathode, which is in turn dependent on the
surface unless an adequate, turbulent sample flow is main-
diffusion rate through the membrane. The less noble anode,
tained. The manufacturer’s minimum flowrate recommenda-
usually silver or lead, completes the circuit and is oxidized in
tions must be met or exceeded in order to prevent erroneously
proportion to the current flow. At steady state, the resulting
low readings.
current signal is then proportional to the oxygen partial
6.3 Diffusion-type probes are subject to negative errors
pressureofthesample.Thoroughdescriptionsofdiffusion-type
fromthebuildupofcoatingssuchasironoxides,whichimpede
probes are given by Hitchman (1) and Fatt (2).
the diffusion rate of oxygen. (Equilibrium-type probes are not
4.4 Equilibrium-type probes rely on oxygen diffusion subject to errors from flowrate or coating.)
through the membrane only until equilibrium between the
6.4 Calibration must be corrected for barometric pressure
inside and outside is achieved. Oxygen is reduced at the noble
according to the manufacturer‘s recommendations at atmo-
metal cathode, as with diffusion-type probes. However, the
spheric conditions that deviate from a nominal range of 745 to
measuring circuit forces electrical current to flow through the
775 mmHg. See Table 1 for altitude corrections. Calibration
noble metal anode equal and opposite to that at the cathode,
under low-pressure conditions without compensation would
and the resulting oxidation reaction produces oxygen. This is
result in positive measurement errors.
the exact reverse of the reaction at the cathode, so there is no
6.5 The growth of bacteria in sample lines and flow cham-
netconsumptionofoxygenbytheprobe.Itreachesequilibrium
bers and on probe membranes can consume oxygen and cause
in constant DO samples, and no net oxygen diffuses through
negative errors. Chemical sterilization with hydrochloric acid
the membrane. Accuracy is not dependent on membrane
(1 + 44) or sodium hypochlorite solution (10 mg/L) should be
surface condition or sample flowrate.
performed if errors from bacteria growth are suspected.
(Warning—Do not mix hydrochloric acid and sodium hy-
5. Significance and Use
pochlorite since hazardous chlorine gas would be released
5.1 DO may be either a corrosive or passivating agent in
rapidly.)
boiler/steam cycles and is therefore controlled to specific
concentrations that are low relative to environmental and
wastewater treatment samples. Out-of-specification DO con-
TABLE 1 Solubility of Oxygen (mg/L) at Various Temperatures
centrations may cause corrosion in boiler systems, which leads
and Elevations (Based on Sea Level Barometric Pressure of
to corrosion fatigue and corrosion products — all detrimental
760 mmHg) (4)
to the life and efficient operation of a steam generator. The
Temperature, Elevation, ft above Sea Level
efficiency of DO removal from boiler feedwater by mechanical
°C
0 1000 2000 3000 4000 5000 6000
orchemicalmeans,orboth,maybemonitoredbycontinuously
0 14.6 14.1 13.6 13.2 12.7 12.3 11.8
measuring the DO concentration before and after the removal
2 13.8 13.3 12.9 12.4 12.0 11.6 11.2
process with on-line instrumentation. DO measurement is also 4 13.1 12.7 12.2 11.9 11.4 11.0 10.6
6 12.4 12.0 11.6 11.2 10.8 10.4 10.1
a check for air leakage into the boiler water cycle.
8 11.8 11.4 11.0 10.6 10.3 9.9 9.6
10 11.3 10.9 10.5 10.2 9.8 9.5 9.2
5.2 Feedwater chemistry guidelines for high-pressure boil-
12 10.8 10.4 10.1 9.7 9.4 9.1 8.8
ers generally require specific feedwater DO concentrations:
14 10.3 9.9 9.6 9.3 9.0 8.7 8.3
5 µg⁄L or less for reducing all volatile treatment [AVT(R)]; 16 9.9 9.7 9.2 8.9 8.6 8.3 8.0
18 9.5 9.2 8.7 8.6 8.3 8.0 7.7
5–10 µg⁄L for oxidizing all volatile treatment [AVT(O)];
20 9.1 8.8 8.5 8.2 7.9 7.7 7.4
50–200 µg⁄L for oxygenated treatment [OT] (3).
22 8.7 8.4 8.1 7.8 7.7 7.3 7.1
24 8.4 8.1 7.8 7.6 7.3 7.1 6.8
5.3 In microelectronics production, DO can be detrimental
26 8.1 7.8 7.6 7.3 7.0 6.8 6.6
28 7.8 7.5 7.3 7.0 6.8 6.6 6.3
in some manufacturing processes, for example, causing unde-
30 7.5 7.2 7.0 6.8 6.5 6.3 6.1
sirable oxidation on silicon wafers.
32 7.3 7.1 6.8 6.6 6.4 6.1 5.9
34 7.1 6.9 6.6 6.4 6.2 6.0 5.8
36 6.8 6.6 6.3 6.1 5.9 5.7 5.5
38 6.6 6.4 6.2 5.9 5.7 5.6 5.4
The boldface numbers in parentheses refer to the list of references at the end of 40 6.4 6.2 6.0 5.8 5.6 5.4 5.2
this test method.
D5462 − 21
6.6 The passage of high-temperature samples containing of withstanding the flowrate, temperature, and pressure condi-
both DO and an oxygen scavenger through hot sample lines tions of the installation.The probe must incorporate an integral
can allow continued reaction of the two. With long sample precisiontemperaturesensortoensurethatitsensesthesample
lines,theDOmeasuredattheprobemaybesignificantlybelow temperature at which the DO is being detected in order to
that at the sample point. Short sample lines and cooling near ensure accurate temperature compensation with fast response.
the source are recommended. 7.2.4 Diffusion-type probes must have their electrodes,
electrolyte, and membrane serviced or replaced according to
6.7 Volatile oxygen scavengers or suppressants, such as
the manufacturer’s recommendations. Equilibrium-type probes
hydrazine, amines, and hydrogen, that pass through the probe
do not require internal maintenance.
membrane may cause unwanted reactions at the electrodes and
7.2.5 Probe membranes must be cleaned in accordance with
negative errors. The magnitude of errors depends on the
the manufacturer’s recommendations. The cleaning frequency
relative concentrations of DO and the oxygen scavenger or
is determined by experience with the particular sample and
suppressant as well as the type of electrochemical cell used.
must be sufficient to maintain acceptable accuracy with
The probe manufacturer’s cautions and limitations should be
diffusion-type probes (see 6.3). The cleaning of equilibrium-
considered.
type probes is not necessary unless a heavy coating increases
6.8 New sample lines require conditioning to achieve equi-
response time or becomes biologically active (see 6.5).
librium conditions. See Practices D3370 to avoid sampling
interferences. 8. Reagents
6.9 Iron oxides and other deposits accumulate in slow-
8.1 Purity of Reagents—Reagent grade chemicals shall be
flowing horizontal sample lines and can develop used in all tests. Unless otherwise indicated, it is intended that
chromatograph-like retention of dissolved species, resulting in
all reagents shall conform to the specifications of the Commit-
very long delay times. Precautions are described in Section 9. tee onAnalytical Reagents of theAmerican Chemical Society,
where such specifications are available. Other grades may be
6.10 The response time can be slow for large decreases in
used, provided it is first ascertained that the reagent is of
DO. This is especially true of measurements below 10 µg/L
sufficiently high purity to permit its use without lessening the
following air calibration, which corresponds to a concentration
accuracy of the determination.
decrease of 3 to 4 orders of magnitude. Hours may be required
for all traces of oxygen to diffuse out of the probe and to
8.2 Purity of Water—References to water shall be under-
achieve accurate measurements at low µg/L levels. stood to mean water that meets or exceeds the quantitative
specifications for type III reagent water conforming to 1.1 of
7. Apparatus
Specification D1193.
7.1 Measuring Instrument:
8.3 Hydrochloric Acid (1 + 44)—Add 1 volume of concen-
7.1.1 The instrument should have both µg/L(ppb) and mg/L
trated HCl (sp gr 1.19) to 44 volumes of water and mix.
(ppm) range capability. It must have a span calibration adjust-
8.4 Sodium Hypochlorite (10 mg/L)—Add approximately
ment to match the readout to the sensitivity of a particular
0.05 mL (1 drop) of 5 % NaOCl solution (commercial bleach
probe.
is satisfactory for this purpose) to 250 mL of water.
7.1.2 The direct readout of DO concentration requires
temperature compensation for effects of the following: (1) 8.5 Cobalt Chloride Solution, Saturated—Dissolve 4.5 g of
cobalt chloride (CoCl ) in 10 mL of water.
oxygen solubility in water; (2) electrochemical cell output; and
(3) when necessary, diffusion rate of oxygen through the
8.6 Sodium Sulfite Zero Solution (10 g/200 mL)—Dissolve
membrane. During air calibration, the instrument must disable
10 g of sodium sulfite (Na SO ) in 200 mL of water.
2 3
the oxygen solubility portion of the compensation to respond
NOTE 1—To attain zero DO more rapidly, add two drops of saturated
only to
...

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.
Designation: D5462 − 13 D5462 − 21
Standard Test Method for
On-Line Measurement of Low-Level Dissolved Oxygen in
Water
This standard is issued under the fixed designation D5462; 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.
1. Scope
1.1 This test method covers the on-line determination of dissolved oxygen (DO) in water samples primarily in ranges from 0 to
500 μg/L (ppb), although higher ranges may be used for calibration. On-line instrumentation is used for continuous measurements
of DO in samples that are brought through sample lines and conditioned from high-temperature and high-pressure sources when
necessary.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this The values
given in parentheses after SI units are provided for information only and are not considered standard.
1.3 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 specific hazards statements, see 6.5.
1.4 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 Flowing Process Streams
D3864 Guide for On-Line Monitoring Systems for Water Analysis
3. Terminology
3.1 Definitions—Definitions: For definitions of terms used in this test method, refer to Terminology D1129.
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling Water and
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.
Current edition approved June 15, 2013June 1, 2021. Published July 2013June 2021. Originally approved in 1993. Last previous edition approved in 20082013 as
D5462 – 08.D5462 – 13. DOI: 10.1520/D5462-13.10.1520/D5462-21.
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’sstandard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5462 − 21
3.2 Definitions of Terms Specific to This Standard:
3.2.1 diffusion-type probes, n—galvanic or polarographic sensors that depend on the continuous influx of oxygen through the
membrane to develop the electrical signal.
3.2.2 equilibrium-type probes, n—modified polarographic sensing probes that have a negligible influx of oxygen through the
membrane except during changes of sample DO concentration.
3.2.2.1 Discussion—
Oxygen consumption and regeneration balance each other within the probes under stable conditions, and the net flux through the
membrane is insignificant.
3.2.3 galvanic systems, n—sensing probes and measuring instruments that develop an electrical current from two electrodes inside
the probe from which the final measurement is derived.
3.2.4 partial pressure (of oxygen), n—the volume fraction of oxygen multiplied by the total pressure.
3.2.4.1 Discussion—
The partial pressure of oxygen is the actual parameter detected by DO probes, whether in air or dissolved in water.
3.2.5 polarographic systems, n—sensing probes and measuring instruments that include circuitry to control the operating voltage
of the system, usually using a third (reference) electrode in the probe.
4. Summary of Test Method
4.1 Dissolved oxygen is measured by means of an electrochemical cell separated from the sample by a gas-permeable membrane.
Behind the membrane and inside the probe, electrodes immersed in an electrolyte develop an electrical current proportional to the
oxygen partial pressure of the sample.
4.2 The partial pressure signal is temperature compensated automatically to account for variations with temperature of the
following: oxygen solubility in water; electrochemical cell output; and, when necessary, diffusion rate of oxygen through the
membrane. This yields a direct readout in concentration of μg/L (ppb) or mg/L (ppm).
4.3 Diffusion-type probes rely on a continuous diffusion of oxygen through the membrane. Immediately inside the membrane,
oxygen is reduced at the noble metal cathode, usually platinum or gold. An electrical current is developed that is directly
proportional to the arrival rate of oxygen molecules at the cathode, which is in turn dependent on the diffusion rate through the
membrane. The less noble anode, usually silver or lead, completes the circuit and is oxidized in proportion to the current flow. At
steady state, the resulting current signal is then proportional to the oxygen partial pressure of the sample. Thorough descriptions
of diffusion-type probes are given by Hitchman (1) and Fatt (2).
4.4 Equilibrium-type probes rely on oxygen diffusion through the membrane only until equilibrium between the inside and outside
is achieved. Oxygen is reduced at the noble metal cathode, as with diffusion-type probes. However, the measuring circuit forces
electrical current to flow through the noble metal anode equal and opposite to that at the cathode, and the resulting oxidation
reaction produces oxygen. This is the exact reverse of the reaction at the cathode, so there is no net consumption of oxygen by
the probe. It reaches equilibrium in constant DO samples, and no net oxygen diffuses through the membrane. Accuracy is not
dependent on membrane surface condition or sample flowrate.
5. Significance and Use
5.1 DO may be either a corrosive or passivating agent in boiler/steam cycles and is therefore controlled to specific concentrations
that are low relative to environmental and wastewater treatment samples. Out-of-specification DO concentrations may cause
corrosion in boiler systems, which leads to corrosion fatigue and corrosion products—all products — all detrimental to the life and
efficient operation of a steam generator. The efficiency of DO removal from boiler feedwater by mechanical or chemical means,
or both, may be monitored by continuously measuring the DO concentration before and after the removal process with on-line
instrumentation. DO measurement is also a check for air leakage into the boiler water cycle.
The boldface numbers in parentheses refer to the list of references at the end of this test method.
D5462 − 21
5.2 Guidelines for feedwater to high-pressure boilers with Feedwater chemistry guidelines for high-pressure boilers generally
require specific feedwater DO concentrations: 5 μg ⁄L or less for reducing all volatile treatment generally require[AVT(R)];
5–10 μg a feedwater DO concentration below 5 μg/L⁄L for oxidizing all volatile treatment [AVT(O)]; 50–200 μg ⁄L for oxygenated
treatment [OT] (3).
5.3 Boiler feedwater with oxygenated treatment is maintained in a range of 50 to 300 μg/L DO (4).
5.3 In microelectronics production, DO can be detrimental in some manufacturing processes, for example, causing undesirable
oxidation on silicon wafers.
6. Interferences
6.1 The leakage of atmospheric air into samples is sometimes difficult to avoid and detect. Although sample line fittings and
connections to flow chambers may be water tight, it is still possible for air to diffuse through the water film of a joint to contaminate
a low-μg/L sample. Sample flow through fittings, valves and rotometers can create a venturi effect, which draw ambient air into
the sample. Section 9 provides further details on this non-obvious interference.
6.2 Diffusion-type probes consume oxygen and will deplete it from the sample in immediate contact with the membrane surface
unless an adequate, turbulent sample flow is maintained. The manufacturer’smanufacturer’s minimum flowrate recommendations
must be met or exceeded in order to prevent erroneously low readings.
6.3 Diffusion-type probes are subject to negative errors from the buildup of coatings such as iron oxides, which impede the
diffusion rate of oxygen. (Equilibrium-type probes are not subject to errors from flowrate or coating.)
6.4 Calibration must be corrected for barometric pressure according to the manufacturer’smanufacturer‘s recommendations at
atmospheric conditions that deviate from a nominal range of 745 to 775 mmHg. See Table 1 for altitude corrections. Calibration
under low-pressure conditions without compensation would result in positive measurement errors.
6.5 The growth of bacteria in sample lines and flow chambers and on probe membranes can consume oxygen and cause negative
errors. Chemical sterilization with hydrochloric acid (1 + 44) or sodium hypochlorite solution (10 mg/L) should be performed if
errors from bacteria growth are suspected. (Warning—Do not mix hydrochloric acid and sodium hypochlorite since hazardous
chlorine gas would be released rapidly.)
TABLE 1 Solubility of Oxygen (mg/L) at Various Temperatures
and Elevations (Based on Sea Level Barometric Pressure of
760 mmHg) (54)
Temperature, Elevation, ft above Sea Level
° C
0 1000 2000 3000 4000 5000 6000
0 14.6 14.1 13.6 13.2 12.7 12.3 11.8
2 13.8 13.3 12.9 12.4 12.0 11.6 11.2
4 13.1 12.7 12.2 11.9 11.4 11.0 10.6
6 12.4 12.0 11.6 11.2 10.8 10.4 10.1
8 11.8 11.4 11.0 10.6 10.3 9.9 9.6
10 11.3 10.9 10.5 10.2 9.8 9.5 9.2
12 10.8 10.4 10.1 9.7 9.4 9.1 8.8
14 10.3 9.9 9.6 9.3 9.0 8.7 8.3
16 9.9 9.7 9.2 8.9 8.6 8.3 8.0
18 9.5 9.2 8.7 8.6 8.3 8.0 7.7
20 9.1 8.8 8.5 8.2 7.9 7.7 7.4
22 8.7 8.4 8.1 7.8 7.7 7.3 7.1
24 8.4 8.1 7.8 7.6 7.3 7.1 6.8
26 8.1 7.8 7.6 7.3 7.0 6.8 6.6
28 7.8 7.5 7.3 7.0 6.8 6.6 6.3
30 7.5 7.2 7.0 6.8 6.5 6.3 6.1
32 7.3 7.1 6.8 6.6 6.4 6.1 5.9
34 7.1 6.9 6.6 6.4 6.2 6.0 5.8
36 6.8 6.6 6.3 6.1 5.9 5.7 5.5
38 6.6 6.4 6.2 5.9 5.7 5.6 5.4
40 6.4 6.2 6.0 5.8 5.6 5.4 5.2
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6.6 The passage of high-temperature samples containing both DO and an oxygen scavenger through hot sample lines can allow
continued reaction of the two. With long sample lines, the DO measured at the probe may be significantly below that at the sample
point. Short sample lines and cooling near the source are recommended.
6.7 Volatile oxygen scavengers or suppressants, such as hydrazine, amines, and hydrogen, that pass through the probe membrane
may cause unwanted reactions at the electrodes and negative errors. The magnitude of errors depends on the relative concentrations
of DO and the oxygen scavenger or suppressant as well as the type of electrochemical cell used. The probe
manufacturer’smanufacturer’s cautions and limitations should be considered.
6.8 New sample lines require conditioning to achieve equilibrium conditions. See Practices D3370 to avoid sampling
interferences.
6.9 Iron oxides and other deposits accumulate in slow-flowing horizontal sample lines and can develop chromatograph-like
retention of dissolved species, resulting in very long delay times. Precautions are described in Section 99.
6.10 The response time can be slow for large decreases in DO. This is especially true of measurements below 10 μg/L following
air calibration, which corresponds to a concentration decrease of 3 to 4 orders of magnitude. Hours may be required for all traces
of oxygen to diffuse out of the probe and to achieve accurate measurements at low μg/L levels.
7. Apparatus
7.1 Measuring Instrument:
7.1.1 The instrument should have both μg/L (ppb) and mg/L (ppm) range capability. It must have a span calibration adjustment
to match the readout to the sensitivity of a particular probe.
7.1.2 The direct readout of DO concentration requires temperature compensation for effects of the following: (1) oxygen solubility
in water; (2) electrochemical cell output; and (3) when necessary, diffusion rate of oxygen through the membrane. During air
calibration, the instrument must disable the oxygen solubility portion of the compensation to respond only to partial pressure.
7.1.3 If included, electrical output signal(s) from the instrument must be isolated from the probe measuring circuit and from earth
ground in order to prevent ground loop problems when the instrument is connected to grounded external devices.
7.2 Probe:
7.2.1 Diffusion-type probes use galvanic or polarographic systems, with a noble metal cathode and oxidizable anode immersed
in an electrolyte and separated from the sample with a polyethylene or fluorocarbon gas-permeable membrane.
7.2.2 Equilibrium-type probes are similar to polarographic probes, except that both the anode and cathode are platinum and the
anode is not oxidized.
7.2.3 A sealed flow-through probe configuration must be used to prevent contamination from the atmosphere, as described in 6.1.
The flowrate must be maintained within the manufacturer’smanufacturer’s recommendations. The probe must be capable of
withstanding the flowrate, temperature, and pressure conditions of the installation. The probe must incorporate an integral precision
temperature sensor to ensure that it senses the sample temperature at which the DO is being detected in order to ensure accurate
temperature compensation with fast response.
7.2.4 Diffusion-type probes must have their electrodes, electrolyte, and membrane serviced or replaced according to the
manufacturer’smanufacturer’s recommendations. Equilibrium-type probes do not require internal maintenance.
7.2.5 Probe membranes must be cleaned in accordance with the manufacturer’smanufacturer’s recommendations. The cleaning
frequency is determined by experience with the particular sample and must be sufficient to maintain acceptable accuracy with
diffusion-type probes (see 6.3). The cleaning of equilibrium-type probes is not necessary unless a heavy coating increases response
time or becomes biologically active (see 6.5).
D5462 − 21
8. Reagents
8.1 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, where
such specifications are available. Other grades may be used, provided it is first
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