1、Designation: D5015 15Standard Test Method forpH of Atmospheric Wet Deposition Samples byElectrometric Determination1This standard is issued under the fixed designation D5015; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is applicable to the determination ofpH in atmospheric wet deposition samples by electrometricmea
3、surement using either a pH half cell with a reference probeor a combination electrode as the sensor.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if
4、any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 WarningMercury has been designated by many regu-latory agencies as a hazardous material
5、 that can cause seriousmedical issues. Mercury, or its vapor, has been demonstrated tobe hazardous to health and corrosive to materials. Cautionshould be taken when handling mercury and mercury contain-ing products. See the applicable product Safety Data Sheet(SDS) for additional information. Users
6、should be aware thatselling mercury or mercury-containing products into your stateor country may be prohibited by law.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD1356 Terminology Relating to Sampling and Analysis ofAtmospheresD2
7、777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD5012 Guide for Preparation of Materials Used for theCollection and Preservation of Atmospheric Wet Deposi-tionD5111 Guide for Choosing Locations and Sampling Meth-ods to Monitor Atmospheric Depos
8、ition at Non-UrbanLocationsE1 Specification for ASTM Liquid-in-Glass ThermometersE2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision LiquidsIEEE/ASTM SI-10 American National Standard for MetricPractice3. Terminology3.1 Definitions:3.1.1 pHthe negative logarithm to th
9、e base ten of theconventional hydrogen ion activity.3.1.2 For definitions of other terms used in this test method,refer to Terminologies D1129 and D1356. For an explanationof the metric system including units, symbols, and conversionfactors, see IEEE/ASTM SI-10.4. Summary of Test Method4.1 The pH me
10、ter and the associated electrodes are cali-brated with two reference buffer solutions that bracket theanticipated sample pH. The pH of the wet deposition sample isdetermined from this calibration and a quality control standard.The quality control standard is necessary in this application toevaluate
11、the bias due to residual liquid junction potentials andto correct for this bias.4.2 The pH of a solution is related to the EMF (millivolts)of a pH electrode system according to the operational definitionfor a two-point calibration:pHX! 5 pHS1!1EX2 ES1ES22 ES1pHS2! 2 pHS1!# (1)where:pH (X) = pH of an
12、 unknown sample,pH(S1) = pH of a Standard Solution 1,pH(S2) = pH of a Standard Solution 2,EX= EMF (mV) measured in an unknown sample,ES1= EMF (mV) measured in Standard Solution 1, andES2= EMF (mV) measured in Standard Solution 2.1This test method is under the jurisdiction of ASTM Committee D22 on Ai
13、rQuality and is the direct responsibility of Subcommittee D22.03 on AmbientAtmospheres and Source Emissions.Current edition approved April 1, 2015. Published April 2015. Originallyapproved in 1989. Last previous edition approved in 2008 as D5015 02 (2008).DOI: 10.1520/D5015-15.2For referenced ASTM s
14、tandards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
15、, PA 19428-2959. United States15. Significance and Use5.1 The accurate measurement of pH in atmospheric wetdeposition is an essential and critically important component inthe monitoring of atmospheric wet deposition for trends in theacidity and overall air quality. Atmospheric wet deposition is,in g
16、eneral, a low ionic strength, unbuffered solution. Specialprecautions, as detailed in this test method, are necessary toensure accurate pH measurements (1).3Special emphasis mustbe placed on minimizing the effect of the residual liquidjunction potential bias.5.2 This test method is applicable only t
17、o the measurementof pH in atmospheric wet deposition. Its use in other applica-tions may result in inaccuracies.5.3 Fig. 1 provides a frequency distribution of precipitationpH values measured in conjunction with a national monitoringprogram within the United States. These data are an indicationof th
18、e range of pH values common to atmospheric wetdeposition.6. Interferences6.1 The pH meter and the associated electrodes reliablymeasure pH in nearly all aqueous solutions and in general arenot subject to solution interferences from color, turbidity,oxidants, or reductants.6.2 The pH of an aqueous so
19、lution is affected by thetemperature. The electromotive force (EMF) between the glassand the reference electrode is a function of temperature as wellas pH. Temperature effects can be approximately compensatedfor automatically or manually depending on the pH meterselected.6.3 Organic materials disper
20、sed in water appear to poisonthe glass electrode, particularly when analyzing low ionicstrength solutions. Difficulty encountered when standardizingthe electrode(s), erratic readings, or slow response times maybe an indication of contamination of the glass bulb or the liquidjunction of the reference
21、 electrode. To remove these coatings,refer to the manual accompanying the probe for the manufac-turers recommendations.6.4 When analyzing samples that have low ionic strengths,such as wet deposition, an effect known as “residual junctionpotential” can lead to errors as large as 0.3 pH units. This er
22、roroccurs when the junction potential of the sample differs greatlyfrom that of the standard. These conditions are frequently metin wet deposition analyses when the electrodes are calibratedwith high ionic strength standard reference buffers. In manycases, this error has been reduced by using a refe
23、renceelectrode with a ceramic junction (2, 3).6.5 To speed electrode equilibration, the sample should beagitated prior to measurement. Care must be taken, however, toavoid introducing a source of error known as “residual stream-ing potential that can result in a significant differencebetween the sti
24、rred and unstirred pH of the sample (4). Themagnitude of the streaming potential is dependent on theelectrodes and on the stirring rate. Differences in pH for stirredand unstirred wet deposition samples when the electrodeassembly has been calibrated only with quiescent referencestandards average 0.0
25、5 pH units at a stirring rate of fourrevolutions per second.6.5.1 Eliminate the errors associated with residual stream-ing potentials by agitating all calibration standards and wetdeposition samples thoroughly to speed electrode equilibrationand then allowing each aliquot to become quiescent beforet
26、aking a pH reading.6.5.2 If magnetic stirring is used, take care not to contami-nate the sample when inserting the stirring bar. Maintain an airspace between the surface of the stirring motor and the samplecontainer to prevent heating the wet deposition sample.6.6 Laboratories used for the measureme
27、nts of pH should befree from gaseous and particulate contaminants that may affectthe true solution pH. Fumes from mineral acids such ashydrochloric acid, sulfuric acid, and nitric acid should be keptisolated from areas where pH measurements are made as wellas alkaline fumes from solutions such as am
28、monia.7. Apparatus and Equipment7.1 Laboratory pH MeterThe meter may have either ananalog or digital display with a readability of at least 0.01 pHunits. A meter that has separate calibration and slope adjust-ment features and is electrically shielded to avoid interferencesfrom stray currents or sta
29、tic charge is necessary. It may bepowered by battery or 110 VAC; if battery powered, the metermust have a battery check feature. A temperature compensatorcontrol for measurements at temperatures other than 25C isdesirable.7.2 Sensing ElectrodeSelect a general purpose glass elec-trode that meets the
30、performance criteria described in 12.2.This electrode type is characterized by a quick response, andhas a useful range from 2 to 11 pH units. This electrode shouldbe used exclusively for atmospheric wet deposition measure-ments.7.3 Reference ElectrodeThe reference electrode recom-mended for wet depo
31、sition analysis is one equipped with a3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.FIG. 1 Frequency Distribution of Measured Laboratory pH of At-mospheric Wet Deposition From the 1984 National AtmosphericDeposition Program (NADP)/National Trends Net
32、work (NTN)D5015 152ceramic junction with controlled leakage of the internal elec-trolyte fill solution. The ceramic construction minimizes dif-ferences in potential between high ionic strength buffers andlow ionic strength samples thus reducing errors from residualjunction potential (1). This electr
33、ode should be used exclu-sively for atmospheric wet deposition measurements.7.4 Combination ElectrodeThe combination electrodecombines the indicating and reference elements in a single unit.A ceramic reference junction is recommended (see 7.3). Sincesample volume requirements are a consideration whe
34、n analyz-ing wet deposition samples, combination electrodes are moreconvenient than separate glass and reference electrodes. Thiselectrode should be used exclusively for atmospheric wetdeposition measurements and must meet the criteria stated in12.2.7.5 Temperature ControlUse either a constant tempe
35、raturewater bath, a temperature compensator, or a thermometer (seeSpecifications E1 or E2251) to verify that all standards andsamples are maintained at temperatures within 61C of oneanother. If a thermometer is used, select one capable of beingread to the nearest 1C and covering the range from 0 to
36、40C.7.6 Stirring Device (Optional)Electric or water-driven. Ifan electric stirrer is selected, leave an air gap or place aninsulating pad between the stirrer surface and the solutioncontainer to minimize heating of the sample. Use afluorocarbon-coated stirring bar.7.7 Storage of ElectrodesWhen not i
37、n use, soak theelectrodes in a solution that is 0.1 mol/L of potassium chlorideand 0.1 mmol/L of hydrochloric acid. Do not store theelectrodes in buffers, concentrated acids, concentrated potas-sium chloride, basic solutions, or distilled water. Some manu-facturers recommend dry storage for specific
38、 types of elec-trodes. If the electrode is of this specific type, store dry. Usethese electrodes exclusively for atmospheric wet depositionmeasurements.8. Reagents and Materials8.1 Purity of ReagentsUse reagent or higher grade chemi-cals for all solutions. All reagents shall conform minimally tothe
39、specifications of the Committee on Analytical Reagents ofthe American Chemical Society (ACS)4where such specifica-tions are available.8.2 Purity of WaterUse water conforming to SpecificationD1193, Type I. Point of use 0.2 m filters are recommended forall faucets supplying ASTM Type I water to preven
40、t theintroduction of bacteria or ion exchange resins into reagents,standard solutions, and internally formulated quality controlcheck solutions.8.3 Buffer SolutionsEither NIST buffers or commerciallyavailable buffer solutions traceable to NIST buffers must beused for standardization. These buffer so
41、lutions usually havepH values near 3, 4, 6, and 7, the exact pH and use temperaturebeing provided by the supplier of the specific buffer. Table 1identifies each buffer salt by its National Institute of Standardsand Technology (NIST) number. Store the reference buffersolutions in polyethylene or chem
42、ical-resistant glass bottlesand replace after one year or sooner if a visible change such asthe development of colloidal or particulate materials is ob-served. Follow the directions on the Certificate of Analysis forpreparing solutions of known pH (5).8.4 Quality Control Sample (QCS)Quality controls
43、amples of verified pH in an atmospheric wet deposition matrixare to be used. Internally formulated quality control samples(see 8.4.1) may be prepared by dilutions of strong acids withwater. The pH of such samples must be verified by comparisonwith a NIST traceable low-ionic strength solution of know
44、npH.8.4.1 Dilute Nitric Acid (5.0 105mol/LHNO3)Add 1.0mL of concentrated nitric acid (HNO3, sp gr 1.42) to 0.5 Lwater, dilute to 1 L and mix well. Dilute 3.2 mL of this stocksolution to 1 L with water. The resulting solution has a pH of4.30 6 0.10 at 25C. Store at room temperature in a high-density
45、polyethylene or polypropylene container. Various fac-tors may affect the stability of this solution. Verify the pH ofthis solution with a NIST traceable standard at monthlyintervals.9. Safety Hazards9.1 The reference buffer solutions, sample types, and mostreagents used in this test method pose no h
46、azard to the analystas used in this test method. Use a fume hood, protectiveclothing, and safety glasses when handling concentrated nitricacid.9.2 Follow American Chemical Society guidelines regard-ing the safe handling of chemicals used in this test method (6).10. Sample Collection, Preservation, a
47、nd Storage10.1 Collect samples in high-density polyethylene (HDPE)containers that have been thoroughly rinsed with water. Do notuse strong mineral acids or alkaline detergent solutions forcleaning collection vessels. Residual acids may remain in thepolyethylene matrix and slowly leach back into the
48、sample.Alkaline detergents may also leave residues that may affect thesample chemistry. Cap collection containers after cleaning toprevent contamination from airborne contaminants; air drycollection containers in a laminar flow clean air work stationand wrap in polyethylene bags prior to use. If a l
49、aminar flow4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.TABLE 1 National Institute of Standards and Technology (NIST)Salts for Reference Buffer SolutionsNIST StandardSample DesignationBuffer SaltApH at 25C186-lf potass
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