ASTM D5015-02(2008)

Standard Test Method for pH of Atmospheric Wet Deposition Samples by Electrometric Determination

SIGNIFICANCE AND USE
The accurate measurement of pH in atmospheric wet deposition is an essential and critically important component in the monitoring of atmospheric wet deposition for trends in the acidity and overall air quality. Atmospheric wet deposition is, in general, a low ionic strength, unbuffered solution. Special precautions, as detailed in this test method, are necessary to ensure accurate pH measurements (1). Special emphasis must be placed on minimizing the effect of the residual liquid junction potential bias.
This test method is applicable only to the measurement of pH in atmospheric wet deposition. Its use in other applications may result in inaccuracies.
Fig. 1 provides a frequency distribution of precipitation pH values measured in conjunction with a national monitoring program within the United States. These data are an indication of the range of pH values common to atmospheric wet deposition.
FIG. 1 Frequency Distribution of Measured Laboratory pH of Atmospheric Wet Deposition From the 1984 National Atmospheric Deposition Program (NADP)/National Trends Network (NTN)
SCOPE
1.1 This test method is applicable to the determination of pH in atmospheric wet deposition samples by electrometric measurement using either a pH half cell with a reference probe or a combination electrode as the sensor.  
1.2 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Jul-2008
• ICS: 71.040.50 - Physicochemical methods of analysis
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.03 - Ambient Atmospheres and Source Emissions

Relations

• Replaces: ASTM D5015-02 - Standard Test Method for pH of Atmospheric Wet Deposition Samples by Electrometric Determination
• Effective Date: 01-Aug-2008
• Referred By: ASTM D6328-18 - Standard Guide for Quality Assurance Protocols for Chemical Analysis of Atmospheric Wet Deposition
• Effective Date: 01-Aug-2008
• Referred By: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Aug-2008

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D5015 − 02(Reapproved 2008)
Standard Test Method for
pH of Atmospheric Wet Deposition Samples by
Electrometric Determination
This standard is issued under the fixed designation D5015; 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.
1. Scope 3.1.2 Fordefinitionsofothertermsusedinthistestmethod,
refer toTerminology D1129 and D1356. For an explanation of
1.1 This test method is applicable to the determination of
the metric system including units, symbols, and conversion
pH in atmospheric wet deposition samples by electrometric
factors, see Practice IEEE/ASTM SI-10.
measurementusingeitherapHhalfcellwithareferenceprobe
or a combination electrode as the sensor.
4. Summary of Test Method
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 4.1 The pH meter and the associated electrodes are cali-
responsibility of the user of this standard to establish appro-
brated with two reference buffer solutions that bracket the
priate safety and health practices and determine the applica- anticipatedsamplepH.ThepHofthewetdepositionsampleis
bility of regulatory limitations prior to use.
determinedfromthiscalibrationandaqualitycontrolstandard.
The quality control standard is necessary in this application to
2. Referenced Documents
evaluate the bias due to residual liquid junction potentials and
2.1 ASTM Standards: to correct for this bias.
D1129Terminology Relating to Water
4.2 The pH of a solution is related to the EMF (millivolts)
D1193Specification for Reagent Water
ofapHelectrodesystemaccordingtotheoperationaldefinition
D1356Terminology Relating to Sampling and Analysis of
for a two-point calibration:
Atmospheres
E 2 E
D2777Practice for Determination of Precision and Bias of
X S
pH X 5pH S 1 pH S 2pH S (1)
~ ! ~ ! @ ~ ! ~ !#
1 2 1
Applicable Test Methods of Committee D19 on Water E 2 E
S S
2 1
D5012Guide for Preparation of Materials Used for the
where:
Collection and Preservation of Atmospheric Wet Deposi-
pH (X) = pH of an unknown sample,
tion
pH(S ) = pH of a Standard Solution 1,
D5111Guide for Choosing Locations and Sampling Meth-
pH(S ) = pH of a Standard Solution 2,
ods to Monitor Atmospheric Deposition at Non-Urban
E = EMF (mV) measured in an unknown sample,
X
Locations
E = EMF(mV)measuredinStandardSolution1,and
S
E1Specification for ASTM Liquid-in-Glass Thermometers
E = EMF (mV) measured in Standard Solution 2.
S
IEEE/ASTM SI-10Standard for Use of the International
System of Units (SI): The Modern Metric System
5. Significance and Use
3. Terminology
5.1 The accurate measurement of pH in atmospheric wet
3.1 Definitions:
depositionisanessentialandcriticallyimportantcomponentin
3.1.1 pH—the negative logarithm to the base ten of the
the monitoring of atmospheric wet deposition for trends in the
conventional hydrogen ion activity.
acidity and overall air quality. Atmospheric wet deposition is,
in general, a low ionic strength, unbuffered solution. Special
precautions, as detailed in this test method, are necessary to
This test method is under the jurisdiction of ASTM Committee D22 on Air
Quality and is the direct responsibility of Subcommittee D22.03 on Ambient
ensure accurate pH measurements (1). Special emphasis must
Atmospheres and Source Emissions.
be placed on minimizing the effect of the residual liquid
Current edition approved Aug. 1, 2008. Published September 2008. Originally
junction potential bias.
approved in 1989. Last previous edition approved in 2002 as D5015–02. DOI:
10.1520/D5015-02R08.
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 Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5015 − 02 (2008)
ing potential’’ that can result in a significant difference
between the stirred and unstirred pH of the sample (4). The
magnitude of the streaming potential is dependent on the
electrodesandonthestirringrate.DifferencesinpHforstirred
and unstirred wet deposition samples when the electrode
assembly has been calibrated only with quiescent reference
standards average 0.05 pH units at a stirring rate of four
revolutions per second.
6.5.1 Eliminate the errors associated with residual stream-
ing potentials by agitating all calibration standards and wet
deposition samples thoroughly to speed electrode equilibration
and then allowing each aliquot to become quiescent before
taking a pH reading.
FIG. 1 Frequency Distribution of Measured Laboratory pH of At-
6.5.2 If magnetic stirring is used, take care not to contami-
mospheric Wet Deposition From the 1984 National Atmospheric
natethesamplewheninsertingthestirringbar.Maintainanair
Deposition Program (NADP)/National Trends Network (NTN)
space between the surface of the stirring motor and the sample
container to prevent heating the wet deposition sample.
5.2 This test method is applicable only to the measurement
6.6 LaboratoriesusedforthemeasurementsofpHshouldbe
of pH in atmospheric wet deposition. Its use in other applica-
freefromgaseousandparticulatecontaminantsthatmayaffect
tions may result in inaccuracies.
the true solution pH. Fumes from mineral acids such as
5.3 Fig. 1 provides a frequency distribution of precipitation hydrochloric acid, sulfuric acid, and nitric acid should be kept
pH values measured in conjunction with a national monitoring
isolated from areas where pH measurements are made as well
program within the United States.These data are an indication as alkaline fumes from solutions such as ammonia.
of the range of pH values common to atmospheric wet
deposition. 7. Apparatus and Equipment
7.1 Laboratory pH Meter—The meter may have either an
6. Interferences
analog or digital display with a readability of at least 0.01 pH
6.1 The pH meter and the associated electrodes reliably
units. A meter that has separate calibration and slope adjust-
measure pH in nearly all aqueous solutions and in general are
mentfeaturesandiselectricallyshieldedtoavoidinterferences
not subject to solution interferences from color, turbidity,
from stray currents or static charge is necessary. It may be
oxidants, or reductants.
powered by battery or 110 VAC; if battery powered, the meter
6.2 The pH of an aqueous solution is affected by the must have a battery check feature.Atemperature compensator
control for measurements at temperatures other than 25°C is
temperature.Theelectromotiveforce(EMF)betweentheglass
andthereferenceelectrodeisafunctionoftemperatureaswell desirable.
as pH.Temperature effects can be approximately compensated
7.2 Sensing Electrode—Select a general purpose glass elec-
for automatically or manually depending on the pH meter
trode that meets the performance criteria described in 12.2.
selected.
This electrode type is characterized by a quick response, and
6.3 Organic materials dispersed in water appear to poison hasausefulrangefrom2to11pHunits.Thiselectrodeshould
be used exclusively for atmospheric wet deposition measure-
the glass electrode, particularly when analyzing low ionic
strength solutions. Difficulty encountered when standardizing ments.
the electrode(s), erratic readings, or slow response times may
7.3 Reference Electrode—The reference electrode recom-
beanindicationofcontaminationoftheglassbulbortheliquid
mended for wet deposition analysis is one equipped with a
junction of the reference electrode. To remove these coatings,
ceramic junction with controlled leakage of the internal elec-
refer to the manual accompanying the probe for the manufac-
trolyte fill solution. The ceramic construction minimizes dif-
turer’s recommendations.
ferences in potential between high ionic strength buffers and
6.4 When analyzing samples that have low ionic strengths, low ionic strength samples thus reducing errors from residual
such as wet deposition, an effect known as “residual junction junction potential (1). This electrode should be used exclu-
potential”canleadtoerrorsaslargeas0.3pHunits.Thiserror sively for atmospheric wet deposition measurements.
occurswhenthejunctionpotentialofthesamplediffersgreatly
7.4 Combination Electrode—The combination electrode
from that of the standard. These conditions are frequently met
combinestheindicatingandreferenceelementsinasingleunit.
in wet deposition analyses when the electrodes are calibrated
Aceramic reference junction is recommended (see 7.3). Since
with high ionic strength standard reference buffers. In many
sample volume requirements are a consideration when analyz-
cases, this error has been reduced by using a reference
ing wet deposition samples, combination electrodes are more
electrode with a ceramic junction (2, 3).
convenient than separate glass and reference electrodes. This
6.5 To speed electrode equilibration, the sample should be electrode should be used exclusively for atmospheric wet
agitatedpriortomeasurement.Caremustbetaken,however,to deposition measurements and must meet the criteria stated in
avoidintroducingasourceoferrorknownas“residualstream- 12.2.
D5015 − 02 (2008)
TABLE 1 National Institute of Standards and Technology (NIST)
solutions in polyethylene or chemical-resistant glass bottles
Salts for Reference Buffer Solutions
andreplaceafteroneyearorsoonerifavisiblechangesuchas
NIST Standard
A the development of colloidal or particulate materials is ob-
Buffer Salt pH at 25°C
Sample Designation
served. Follow the directions on the Certificate ofAnalysis for
186-lf potassium dihydrogen phosphate, 0.025 M 6.865
preparing solutions of known pH (5).
186-lif disodium hydrogen phosphate, 0.025 M 6.865
185g potassium hydrogen phthalate 4.003
8.4 Quality Control Sample (QCS)—Quality control
A
These buffer salts can be purchased from the Office of Standard Reference
samplesofverifiedpHinanatmosphericwetdepositionmatrix
Materials, National Institute of Standards and Technology, Gaithersburg, MD
are to be used. Internally formulated quality control samples
20899.
(see 8.4.1) may be prepared by dilutions of strong acids with
water.ThepHofsuchsamplesmustbeverifiedbycomparison
with a NIST traceable low-ionic strength solution of known
7.5 TemperatureControl—Useeitheraconstanttemperature
pH.
water bath, a temperature compensator, or a thermometer (see
−5
8.4.1 Dilute NitricAcid(5.0×10 mol/LHNO )—Add1.0
Specification E1) to verify that all standards and samples are 3
mL of concentrated nitric acid (HNO , sp gr 1.42) to 0.5 L
maintained at temperatures within 61°C of one another. If a 3
water, dilute to 1 L and mix well. Dilute 3.2 mL of this stock
thermometer is used, select one capable of being read to the
solution to 1 L with water. The resulting solution has a pH of
nearest 1°C and covering the range from 0 to 40°C.
4.30 6 0.10 at 25°C. Store at room temperature in a high-
7.6 Stirring Device (Optional)—Electric or water-driven. If
density polyethylene or polypropylene container. Various fac-
an electric stirrer is selected, leave an air gap or place an
tors may affect the stability of this solution. Verify the pH of
insulating pad between the stirrer surface and the solution
this solution with a NIST traceable standard at monthly
container to minimize heating of the sample. Use a
intervals.
fluorocarbon-coated stirring bar.
7.7 Storage of Electrodes—When not in use, soak the
9. Safety Hazards
electrodes in a solution that is 0.1 mol/Lof potassium chloride
9.1 The reference buffer solutions, sample types, and most
and 0.1 mmol/L of hydrochloric acid. Do not store the
reagents used in this test method pose no hazard to the analyst
electrodes in buffers, concentrated acids, concentrated potas-
as used in this test method. Use a fume hood, protective
sium chloride, basic solutions, or distilled water. Some manu-
clothing, and safety glasses when handling concentrated nitric
facturers recommend dry storage for specific types of elec-
acid.
trodes. If the electrode is of this specific type, store dry. Use
these electrodes exclusively for atmospheric wet deposition
9.2 Follow American Chemical Society guidelines regard-
measurements.
ingthesafehandlingofchemicalsusedinthistestmethod (6).
8. Reagents and Materials
10. Sample Collection, Preservation, and Storage
8.1 Purity of Reagents—Usereagentorhighergradechemi-
10.1 Collect samples in high-density polyethylene (HDPE)
cals for all solutions. All reagents shall conform minimally to
containersthathavebeenthoroughlyrinsedwithwater.Donot
the specifications of the Committee onAnalytical Reagents of
4 use strong mineral acids or alkaline detergent solutions for
theAmerican Chemical Society (ACS) where such specifica-
cleaning collection vessels. Residual acids may remain in the
tions are available.
polyethylene matrix and slowly leach back into the sample.
8.2 Purity of Water—UsewaterconformingtoSpecification
Alkalinedetergentsmayalsoleaveresiduesthatmayaffectthe
D1193,TypeI.Pointofuse0.2µmfiltersarerecommendedfor
sample chemistry. Cap collection containers after cleaning to
all faucets supplying ASTM Type I water to prevent the
prevent contamination from airborne contaminants; air dry
introduction of bacteria or ion exchange resins into reagents,
collection containers in a laminar flow clean air work station
standard solutions, and internally formulated quality control
and wrap in polyethylene bags prior to use. If a laminar flow
check solutions.
work station is not available, pour out any residual rinse water
and bag or cap the containers immediately. Do not dry the
8.3 Buffer Solutions—Either NIST buffers or commercially
container’s interior by any method other than air drying in a
available buffer solutions traceable to NIST buffers must be
laminar flow clean air work station.
used for standardization. These buffer solutions usually have
pHvaluesnear3,4,6,and7,theexactpHandusetemperature
10.2 The frequency of sample collection and the choice of
being provided by the supplier of the specific buffer. Table 1
sampler design are dependent on the monitoring objectives.
identifies each buffer salt by its National Institute of Standards
GuideD5111furtherdiscussessomeoftheseissues.Ingeneral,
and Technology (NIST) number. Store the reference buffer
the use of wet-only samplers is recommended to exclude dry
deposition contributions, minimize sample co
...

This document is not anASTM standard and is intended only to provide the user of anASTM 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:D5015–95 Designation:D5015–02 (Reapproved 2008)
Standard Test Method for
pH of Atmospheric Wet Deposition Samples by
Electrometric Determination
This standard is issued under the fixed designation D5015; 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.
1. Scope
1.1 This test method is applicable to the determination of pH in atmospheric wet deposition samples by electrometric
measurement using either a pH half cell with a reference probe or a combination electrode as the sensor.
1.2 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1193Specification for Reagent Water Specification for Reagent Water
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D-19D19 on Water
D5012 Guide for Preparation of Materials Used for the Collection and Preservation of Atmospheric Wet Deposition
D5111 Guide for Choosing Locations and Sampling Methods to Monitor Atmospheric Deposition at Non-Urban Locations
E1 Specification for ASTM Liquid-in-Glass Thermometers
E380Practice for Use of the International System of Units (SI) (the Modernized Metric System) IEEE/ASTM SI-10 Standard
for Use of the International
System of Units (SI): The
Modern Metric System
3. Terminology
3.1 Definitions:
3.1.1 pH—the negative logarithm to the base ten of the conventional hydrogen ion activity.
3.1.2 For definitions of other terms used in this test method, refer to Terminology D1129 and D1356. For an explanation of
the metric system including units, symbols, and conversion factors, see Practice E380.
4. Summary of Test Method
4.1 The pH meter and the associated electrodes are calibrated with two reference buffer solutions that bracket the anticipated
sample pH. The pH of the wet deposition sample is determined from this calibration and a quality control standard. The quality
controlstandardisnecessaryinthisapplicationtoevaluatethebiasduetoresidualliquidjunctionpotentialsandtocorrectforthis
bias.
4.2 The pH of a solution is related to the EMF (millivolts) of a pH electrode system according to the operational definition for
a two-point calibration:
E 2 E
X S
pH ~X! 5pH ~S ! 1 [pH ~S ! 2pH ~S !# (1)
1 2 1
E 2 E
S S
2 1
This test method is under the jurisdiction ofASTM Committee D-22 on Sampling andAnalysis ofAtmospheres and is the direct responsibility of Subcommittee D22.06
on Atmospheric Deposition.
Current edition approved Jan. 15, 1995. Published March 1995. Originally published as D5015–89. Last previous edition D5015–89.
This test method is under the jurisdiction ofASTM Committee D22 onAir Quality and is the direct responsibility of Subcommittee D22.03 onAmbientAtmospheres
and Source Emissions.
Current edition approved Aug. 1, 2008. Published September 2008. Originally approved in 1989. Last previous edition approved in 2002 as D5015–02.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,[e-mail] Annual Book of ASTM Standards
, Vol 11.01.volume information, refer to the standard’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.
D5015–02 (2008)
where:
pH (X) = pH of an unknown sample,
pH (S ) = pH of a Standard Solution 1,
pH (S ) = pH of a Standard Solution 2,
E = EMF (mV) measured in an unknown sample,
X
E = EMF (mV) measured in Standard Solution 1, and
S
E = EMF (mV) measured in Standard Solution 2.
S
5. Significance and Use
5.1 The accurate measurement of pH in atmospheric wet deposition is an essential and critically important component in the
monitoringofatmosphericwetdepositionfortrendsintheacidityandoverallairquality.Atmosphericwetdepositionis,ingeneral,
a low ionic strength, unbuffered solution. Special precautions, as detailed in this test method, are necessary to ensure accurate pH
measurements (1) . Special emphasis must be placed on minimizing the effect of the residual liquid junction potential bias.
5.2 This test method is applicable only to the measurement of pH in atmospheric wet deposition. Its use in other applications
may result in inaccuracies.
5.3 Fig. 1 provides a frequency distribution of precipitation pH values measured in conjunction with a national monitoring
program within the United States.These data are an indication of the range of pH values common to atmospheric wet deposition.
6. Interferences
6.1 The pH meter and the associated electrodes reliably measure pH in nearly all aqueous solutions and in general are not
subject to solution interferences from color, turbidity, oxidants, or reductants.
6.2 The pH of an aqueous solution is affected by the temperature. The electromotive force (EMF) between the glass and the
reference electrode is a function of temperature as well as pH. Temperature effects can be approximately compensated for
automatically or manually depending on the pH meter selected.
6.3 Organic materials dispersed in water appear to poison the glass electrode, particularly when analyzing low ionic strength
solutions.Difficultyencounteredwhenstandardizingtheelectrode(s),erraticreadings,orslowresponsetimesmaybeanindication
of contamination of the glass bulb or the liquid junction of the reference electrode. To remove these coatings, refer to the manual
accompanying the probe for the manufacturer’s recommendations.
6.4 When analyzing samples that have low ionic strengths, such as wet deposition, an effect known as “residual junction
potential” can lead to errors as large as 0.3 pH units. This error occurs when the junction potential of the sample differs greatly
from that of the standard. These conditions are frequently met in wet deposition analyses when the electrodes are calibrated with
high ionic strength standard reference buffers. In many cases, this error has been reduced by using a reference electrode with a
ceramic junction (2, 3).
6.5 Tospeedelectrodeequilibration,thesampleshouldbeagitatedpriortomeasurement.Caremustbetaken,however,toavoid
introducingasourceoferrorknownas“residualstreamingpotential’’thatcanresultinasignificantdifferencebetweenthestirred
and unstirred pH of the sample (4). The magnitude of the streaming potential is dependent on the electrodes and on the stirring
rate.DifferencesinpHforstirredandunstirredwetdepositionsampleswhentheelectrodeassemblyhasbeencalibratedonlywith
quiescent reference standards average 0.05 pH units at a stirring rate of four revolutions per second.
Annual Book of ASTM Standards, Vol 11.03.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
FIG. 1 Frequency Distribution of Measured Laboratory pH of
Atmospheric Wet Deposition From the 1984 National
Atmospheric Deposition Program (NADP)/National Trends
Network (NTN)
D5015–02 (2008)
6.5.1 Eliminatetheerrorsassociatedwithresidualstreamingpotentialsbyagitatingallcalibrationstandardsandwetdeposition
samples thoroughly to speed electrode equilibration and then allowing each aliquot to become quiescent before taking a pH
reading.
6.5.2 If magnetic stirring is used, take care not to contaminate the sample when inserting the stirring bar. Maintain an air space
between the surface of the stirring motor and the sample container to prevent heating the wet deposition sample.
6.6 LaboratoriesusedforthemeasurementsofpHshouldbefreefromgaseousandparticulatecontaminantsthatmayaffectthe
true solution pH. Fumes from mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid should be kept isolated from
areas where pH measurements are made as well as alkaline fumes from solutions such as ammonia.
7. Apparatus and Equipment
7.1 Laboratory pH Meter—The meter may have either an analog or digital display with a readability of at least 0.01 pH units.
A meter that has separate calibration and slope adjustment features and is electrically shielded to avoid interferences from stray
currentsorstaticchargeisnecessary.Itmaybepoweredbybatteryor110Vacline;VAC;ifbatterypowered,themetermusthave
a battery check feature. A temperature compensator control for measurements at temperatures other than 25°C is desirable.
7.2 Sensing Electrode—Select a general purpose glass electrode that meets the performance criteria described in 12.2. This
electrode type is characterized by a quick response, and has a useful range from 2 to 11 pH units. This electrode should be used
exclusively for atmospheric wet deposition measurements.
7.3 Reference Electrode—The reference electrode recommended for wet deposition analysis is one equipped with a ceramic
junctionwithcontrolledleakageoftheinternalelectrolytefillsolution.Theceramicconstructionminimizesdifferencesinpotential
betweenhighionicstrengthbuffersandlowionicstrengthsamplesthusreducingerrorsfromresidualjunctionpotential (1).Table
1 lists three possibilities for suitable reference electrodes that have been found to be satisfactory. Other electrodes having similar
characteristics are also suitable. This electrode should be used exclusively for atmospheric wet deposition measurements. ). This
electrode should be used exclusively for atmospheric wet deposition measurements.
7.4 Combination Electrode—The combination electrode combines the indicating and reference elements in a single unit. A
ceramic reference junction is recommended (see 7.3). Since sample volume requirements are a consideration when analyzing wet
deposition samples, combination electrodes are more convenient than separate glass and reference electrodes. This electrode
should be used exclusively for atmospheric wet deposition measurements and must meet the criteria stated in 12.2 .
TABLE 2 1 National Institute of Standards and Technology
(NIST) Salts for Reference Buffer Solutions
NIST Standard
A
Buffer Salt pH at 25°C
Sample Designation
186-Ie potassium dihydrogen phosphate, 0.025 M 6.865
186-lf potassium dihydrogen phosphate, 0.025 M 6.865
186-IIe disodium hydrogen phosphate, 0.025 M
186-lif disodium hydrogen phosphate, 0.025 M 6.865
185g potassium hydrogen phthalate 4.003
A
These buffer salts can be purchased from the Office of Standard Reference
Materials, National Institute of Standards and Technology, Gaithersburg, MD
20899.
7.5 Temperature Control—Use either a constant temperature water bath, a temperature compensator, or a thermometer (see
Specification E1) to verify that all standards and samples are maintained at temperatures within 61°C of one another. If a
thermometer is used, select one capable of being read to the nearest 1°C and covering the range from 0 to 40°C.
7.6 Stirring Device (Optional)—Electricorwater-driven.Ifanelectricstirrerisselected,leaveanairgaporplaceaninsulating
pad between the stirrer surface and the solution container to minimize heating of the sample. Use a fluorocarbon-coated stirring
bar.
7.7 Storage of Electrodes—When not in use, soak the electrodes in a solution that is 0.1 mol/L of potassium chloride and 0.1
mmol/L of hydrochloric acid. Do not store the electrodes in buffers, concentrated acids, concentrated potassium chloride, basic
solutions,ordistilledwater.Somemanufacturersrecommenddrystorageforspecifictypesofelectrodes.Iftheelectrodeisofthis
specific type, store dry. Use these electrodes exclusively for atmospheric wet deposition measurements.
8. Reagents and Materials
8.1 Purity of Reagents—Use reagent or higher grade chemicals for all solutions. All reagents shall conform minimally to the
specifications of the Committee on Analytical Reagents of the American Chemical Society (ACS) where such specifications are
available.
Annual Book of ASTM Standards, Vol 14.03.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. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.
D5015–02 (2008)
8.2 Purity of Water—UsewaterconformingtoSpecificationD1193,TypeII.I.Pointofuse0.2µmfiltersarerecommendedfor
all faucets supplyingASTM Type III water to prevent the introduction of bacteria or ion exchange resins into reagents, standard
solutions, and internally formulated quality control check solutions.
8.3 Buffer Solutions—Either NIST buffers or commercially available buffer solutions traceable to NIST buffers must be used
for standardization. These buffer solutions usually have pH values near 3, 4, 6, and 7, the exact pH and use temperature being
provided by the supplier of the specific buffer.Table 2Table 1 identifies each buffer salt by its National Institute of Standards and
Technology (NIST) number. Store the reference buffer solutions in polyethylene or chemical-resistant glass bottles and replace
after one year or sooner if a visible change such as the development of colloidal or particulate materials is observed. Follow the
directions on the Certificate of Analysis for preparing solutions of known pH (5).
8.4 Quality Control Sample (QCS)—Quality control samples of verified pH in an atmospheric wet deposition matrix are to be
used. Internally formulated quality control samples (see 8.4.1) may be prepared by dilutions of strong acids with water. The pH
of such samples must be verified by comparison with SRM 2694a or other a NIST traceable low-ionic strength solutionssolution
of known pH.
−5
8.4.1 Dilute Nitric Acid (5.0 310 mol/LHNO )—Add1.0mLofconcentratednitricacid(HNO ,spgr1.42)to0.5Lwater,
3 3
dilute to 1 Land mix well. Dilute 3.2 mLof this stock solution to 1 Lwith water. The resulting solution has a pH of 4.30 6 0.10
at 25°C. Store at room temperature in a high-density polyethylene or polypropylene container. Various factors may affec
...