ASTM D5015-15(2022)
(Test Method)Standard Test Method for pH of Atmospheric Wet Deposition Samples by Electrometric Determination
Standard Test Method for pH of Atmospheric Wet Deposition Samples by Electrometric Determination
SIGNIFICANCE AND USE
5.1 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).3 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.
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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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.
1.4 Warning—Mercury has been designated by many regulatory agencies as a hazardous material that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Safety Data Sheet (SDS) for additional information. Users should be aware that selling mercury or mercury-containing products into your state or country may be prohibited by law.
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
Relations
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: D5015 − 15 (Reapproved 2022)
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 D1193Specification for Reagent Water
D1356Terminology Relating to Sampling and Analysis of
1.1 This test method is applicable to the determination of
Atmospheres
pH in atmospheric wet deposition samples by electrometric
D2777Practice for Determination of Precision and Bias of
measurementusingeitherapHhalfcellwithareferenceprobe
Applicable Test Methods of Committee D19 on Water
or a combination electrode as the sensor.
D5012Practice for Preparation of Materials Used for the
1.2 The values stated in SI units are to be regarded as
Collection and Preservation of Atmospheric Wet Deposi-
standard. No other units of measurement are included in this
tion
standard.
D5111Guide for Choosing Locations and Sampling Meth-
1.3 This standard does not purport to address all of the ods to Monitor Atmospheric Deposition at Non-Urban
safety concerns, if any, associated with its use. It is the
Locations
responsibility of the user of this standard to establish appro- E1Specification for ASTM Liquid-in-Glass Thermometers
priate safety, health, and environmental practices and deter-
E2251Specification for Liquid-in-Glass ASTM Thermom-
mine the applicability of regulatory limitations prior to use. eters with Low-Hazard Precision Liquids
1.4 Warning—Mercury has been designated by many regu-
IEEE/ASTM SI-10American National Standard for Metric
latory agencies as a hazardous material that can cause serious Practice
medicalissues.Mercury,oritsvapor,hasbeendemonstratedto
3. Terminology
be hazardous to health and corrosive to materials. Caution
3.1 Definitions:
should be taken when handling mercury and mercury contain-
3.1.1 pH—the negative logarithm to the base ten of the
ing products. See the applicable product Safety Data Sheet
conventional hydrogen ion activity.
(SDS) for additional information. Users should be aware that
selling mercury or mercury-containing products into your state
3.1.2 Fordefinitionsofothertermsusedinthistestmethod,
or country may be prohibited by law.
refer to Terminologies D1129 and D1356. For an explanation
1.5 This international standard was developed in accor- of the metric system including units, symbols, and conversion
dance with internationally recognized principles on standard- factors, see IEEE/ASTM SI-10.
ization established in the Decision on Principles for the
4. Summary of Test Method
Development of International Standards, Guides and Recom-
4.1 The pH meter and the associated electrodes are cali-
mendations issued by the World Trade Organization Technical
brated with two reference buffer solutions that bracket the
Barriers to Trade (TBT) Committee.
anticipatedsamplepH.ThepHofthewetdepositionsampleis
2. Referenced Documents determinedfromthiscalibrationandaqualitycontrolstandard.
The quality control standard is necessary in this application to
2.1 ASTM Standards:
evaluate the bias due to residual liquid junction potentials and
D1129Terminology Relating to Water
to correct for this bias.
4.2 The pH of a solution is related to the EMF (millivolts)
This test method is under the jurisdiction of ASTM Committee D22 on Air
ofapHelectrodesystemaccordingtotheoperationaldefinition
Quality and is the direct responsibility of Subcommittee D22.03 on Ambient
for a two-point calibration:
Atmospheres and Source Emissions.
Current edition approved March 1, 2022. Published April 2022. Originally
E 2 E
X S
approved in 1989. Last previous edition approved in 2015 as D5015–15. DOI:
pH~X! 5pH~S !1 @pH~S ! 2pH~S !# (1)
1 2 1
10.1520/D5015-15R22. E 2 E
S S
2 1
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM where:
Standards volume information, refer to the standard’s Document Summary page on
pH (X) = pH of an unknown sample,
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5015 − 15 (2022)
6.3 Organic materials dispersed in water appear to poison
the glass electrode, particularly when analyzing low ionic
strength solutions. Difficulty encountered when standardizing
the electrode(s), erratic readings, or slow response times may
beanindicationofcontaminationoftheglassbulbortheliquid
junction of the reference electrode. To remove these coatings,
refer to the manual accompanying the probe for the manufac-
turer’s recommendations.
6.4 When analyzing samples that have low ionic strengths,
such as wet deposition, an effect known as “residual junction
potential”canleadtoerrorsaslargeas0.3pHunits.Thiserror
occurswhenthejunctionpotentialofthesamplediffersgreatly
from that of the standard. These conditions are frequently met
FIG. 1 Frequency Distribution of Measured Laboratory pH of At-
in wet deposition analyses when the electrodes are calibrated
mospheric Wet Deposition From the 1984 National Atmospheric
with high ionic strength standard reference buffers. In many
Deposition Program (NADP)/National Trends Network (NTN)
cases, this error has been reduced by using a reference
electrode with a ceramic junction (2, 3).
6.5 To speed electrode equilibration, the sample should be
pH(S ) = pH of a Standard Solution 1,
agitatedpriortomeasurement.Caremustbetaken,however,to
pH(S ) = pH of a Standard Solution 2,
avoidintroducingasourceoferrorknownas“residualstream-
E = EMF (mV) measured in an unknown sample,
X
ing potential’’ that can result in a significant difference
E = EMF(mV)measuredinStandardSolution1,and
S
between the stirred and unstirred pH of the sample (4). The
E = EMF (mV) measured in Standard Solution 2.
S
magnitude of the streaming potential is dependent on the
5. Significance and Use
electrodesandonthestirringrate.DifferencesinpHforstirred
and unstirred wet deposition samples when the electrode
5.1 The accurate measurement of pH in atmospheric wet
assembly has been calibrated only with quiescent reference
depositionisanessentialandcriticallyimportantcomponentin
standards average 0.05 pH units at a stirring rate of four
the monitoring of atmospheric wet deposition for trends in the
revolutions per second.
acidity and overall air quality. Atmospheric wet deposition is,
6.5.1 Eliminate the errors associated with residual stream-
in general, a low ionic strength, unbuffered solution. Special
ing potentials by agitating all calibration standards and wet
precautions, as detailed in this test method, are necessary to
deposition samples thoroughly to speed electrode equilibration
ensure accurate pH measurements (1). Special emphasis must
and then allowing each aliquot to become quiescent before
be placed on minimizing the effect of the residual liquid
taking a pH reading.
junction potential bias.
6.5.2 If magnetic stirring is used, take care not to contami-
5.2 This test method is applicable only to the measurement
natethesamplewheninsertingthestirringbar.Maintainanair
of pH in atmospheric wet deposition. Its use in other applica-
space between the surface of the stirring motor and the sample
tions may result in inaccuracies.
container to prevent heating the wet deposition sample.
5.3 Fig. 1 provides a frequency distribution of precipitation
6.6 LaboratoriesusedforthemeasurementsofpHshouldbe
pH values measured in conjunction with a national monitoring
freefromgaseousandparticulatecontaminantsthatmayaffect
program within the United States.These data are an indication
the true solution pH. Fumes from mineral acids such as
of the range of pH values common to atmospheric wet
hydrochloric acid, sulfuric acid, and nitric acid should be kept
deposition.
isolated from areas where pH measurements are made as well
as alkaline fumes from solutions such as ammonia.
6. Interferences
6.1 The pH meter and the associated electrodes reliably
7. Apparatus and Equipment
measure pH in nearly all aqueous solutions and in general are
7.1 Laboratory pH Meter—The meter may have either an
not subject to solution interferences from color, turbidity,
analog or digital display with a readability of at least 0.01 pH
oxidants, or reductants.
units. A meter that has separate calibration and slope adjust-
6.2 The pH of an aqueous solution is affected by the
mentfeaturesandiselectricallyshieldedtoavoidinterferences
temperature.Theelectromotiveforce(EMF)betweentheglass
from stray currents or static charge is necessary. It may be
andthereferenceelectrodeisafunctionoftemperatureaswell
powered by battery or 110 VAC; if battery powered, the meter
as pH.Temperature effects can be approximately compensated
must have a battery check feature.Atemperature compensator
for automatically or manually depending on the pH meter
control for measurements at temperatures other than 25°C is
selected.
desirable.
7.2 Sensing Electrode—Select a general purpose glass elec-
trode that meets the performance criteria described in 12.2.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. This electrode type is characterized by a quick response, and
D5015 − 15 (2022)
TABLE 1 National Institute of Standards and Technology (NIST)
hasausefulrangefrom2to11pHunits.Thiselectrodeshould
Salts for Reference Buffer Solutions
be used exclusively for atmospheric wet deposition measure-
NIST Standard
ments. A
Buffer Salt pH at 25 °C
Sample Designation
7.3 Reference Electrode—The reference electrode recom-
186-lf potassium dihydrogen phosphate, 0.025 M 6.865
mended for wet deposition analysis is one equipped with a 186-lif disodium hydrogen phosphate, 0.025 M 6.865
185g potassium hydrogen phthalate 4.003
ceramic junction with controlled leakage of the internal elec-
A
These buffer salts can be purchased from the Office of Standard Reference
trolyte fill solution. The ceramic construction minimizes dif-
Materials, National Institute of Standards and Technology, Gaithersburg, MD
ferences in potential between high ionic strength buffers and
20899.
low ionic strength samples thus reducing errors from residual
junction potential (1). This electrode should be used exclu-
sively for atmospheric wet deposition measurements.
introduction of bacteria or ion exchange resins into reagents,
standard solutions, and internally formulated quality control
7.4 Combination Electrode—The combination electrode
combinestheindicatingandreferenceelementsinasingleunit. check solutions.
Aceramic reference junction is recommended (see 7.3). Since
8.3 Buffer Solutions—Either NIST buffers or commercially
sample volume requirements are a consideration when analyz-
available buffer solutions traceable to NIST buffers must be
ing wet deposition samples, combination electrodes are more
used for standardization. These buffer solutions usually have
convenient than separate glass and reference electrodes. This
pHvaluesnear3,4,6,and7,theexactpHandusetemperature
electrode should be used exclusively for atmospheric wet
being provided by the supplier of the specific buffer. Table 1
deposition measurements and must meet the criteria stated in
identifies each buffer salt by its National Institute of Standards
12.2.
and Technology (NIST) number. Store the reference buffer
7.5 TemperatureControl—Useeitheraconstanttemperature solutions in polyethylene or chemical-resistant glass bottles
water bath, a temperature compensator, or a thermometer (see andreplaceafteroneyearorsoonerifavisiblechangesuchas
Specifications E1 or E2251) to verify that all standards and the development of colloidal or particulate materials is ob-
samples are maintained at temperatures within 61°C of one served. Follow the directions on the Certificate ofAnalysis for
another. If a thermometer is used, select one capable of being preparing solutions of known pH (5).
readtothenearest1°Candcoveringtherangefrom0to40°C.
8.4 Quality Control Sample (QCS)—Quality control
samplesofverifiedpHinanatmosphericwetdepositionmatrix
7.6 Stirring Device (Optional)—Electric or water-driven. If
an electric stirrer is selected, leave an air gap or place an are to be used. Internally formulated quality control samples
(see 8.4.1) may be prepared by dilutions of strong acids with
insulating pad between the stirrer surface and the solution
container to minimize heating of the sample. Use a water.ThepHofsuchsamplesmustbeverifiedbycomparison
with a NIST traceable low-ionic strength solution of known
fluorocarbon-coated stirring bar.
pH.
7.7 Storage of Electrodes—When not in use, soak the
−5
8.4.1 Dilute NitricAcid(5.0×10 mol/LHNO )—Add1.0
electrodes in a solution that is 0.1 mol/Lof potassium chloride
mL of concentrated nitric acid (HNO , sp gr 1.42) to 0.5 L
and 0.1 mmol/L of hydrochloric acid. Do not store the
water, dilute to 1 L and mix well. Dilute 3.2 mL of this stock
electrodes in buffers, concentrated acids, concentrated potas-
solution to 1 L with water. The resulting solution has a pH of
sium chloride, basic solutions, or distilled water. Some manu-
4.30 6 0.10 at 25°C. Store at room temperature in a
facturers recommend dry storage for specific types of elec-
high-density polyethylene or polypropylene container. Various
trodes. If the electrode is of this specific type, store dry. Use
factorsmayaffectthestabilityofthissolution.VerifythepHof
these electrodes exclusively for atmospheric wet deposition
this solution with a NIST traceable standard at monthly
measurements.
intervals.
8. Reagents and Materials
9. Safety Hazards
8.1 Purity of Reagents—Usereagentorhighergradechemi-
9.1 The reference buffer solutions, sample types, and most
cals for all solutions. All reagents shall conform minimally to
reagents used in this test method pose no hazard to the analyst
the specifications of the Committee onAnalytical Reagents of
as used in this test method. Use a fume hood, protective
theAmerican Chemical Society (ACS) where such specifica-
clothing, and safety glasses when handling concentrated nitric
tions are available.
acid.
8.2 Purity of Water—UsewaterconformingtoSpecification
9.2 Follow American Chemical Society guidelines regard-
D1193,TypeI.Pointofuse0.2µmfiltersarerecommendedfor
ingthesafehandlingofchemicalsusedinthistestmethod (6).
all faucets supplying ASTM Ty
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