1、Designation: D513 16Standard Test Methods forTotal and Dissolved Carbon Dioxide in Water1This standard is issued under the fixed designation D513; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 These test methods cover the measurement of total ordissolved carbon dioxide present as carbon dioxide (CO2),carbonic acid, bicarbonate ion,
3、and carbonate ion in water:Range SectionsTest Method A (Gas Sensing Electrode) 2 to 800 mg/L 8 to 15Test Method B (CO2Evolution, CoulometricTitration)5 to 800 mg/L 16 to 241.2 Carbon dioxide may also be detected from carbonatespresent in particulates in samples.1.3 Test Method A is applicable to var
4、ious natural watersand brines.1.4 Test Method B is applicable to natural waters, brines,and various industrial waters as delineated in 16.4.1.5 It is the users responsibility to ensure the validity ofthese test methods on waters of untested matrices.1.6 Several test methods were discontinued from th
5、is stan-dard in 1988. Refer to Appendix X1 for historical information.1.7 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use.
6、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.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Spec
7、ification for Reagent WaterD1293 Test Methods for pH of WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD5847 Practice for Writing Quality Control Specificationsfor Standard Test Met
8、hods for Water AnalysisE200 Practice for Preparation, Standardization, and Storageof Standard and Reagent Solutions for Chemical Analysis3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard, refer toTerminology D1129.4. Significance and Use4.1 Carbon dioxide is a respir
9、ation product of plants andanimals and a decomposition product of organic matter andcertain minerals. The atmosphere averages about 0.04 vol % ofCO2. Surface waters generally contain less than 10 mg/L,except at local points of abnormal organic or mineral decom-position; however, underground water, p
10、articularly deepwaters, may contain several hundred mg/L.4.2 When dissolved in water, CO2contributes significantlyto corrosion of water-handling systems. This is particularlytroublesome in steam condensate systems. Loss of CO2froman aqueous system can disturb the carbonate equilibrium andresult in c
11、alcite encrustation of confining surfaces. Scaling ofwater heaters is a good example. Because of the delicatebalance between corrosion and encrustation tendencies, muchcare must be given to control of CO2and related species inwater systems. Recarbonation of municipal supplies duringfinal stages of s
12、oftening and amine neutralization of steamcondensate are applied for these purposes.5. Purity of Reagents5.1 Reagent grade chemicals shall be used in all tests.Unless otherwise indicated, it is intended that all reagents shallconform to the specifications of the Committee on Analytical1These test me
13、thods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Subcommittee D19.05 on InorganicConstituents in Water.Current edition approved June 15, 2016. Published June 2016. Originallyapproved in 1938. Last previous edition approved in 2011 as D513 111. DOI:1
14、0.1520/D0513-16.2For referenced ASTM standards, 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.*A Summary of Changes section appears at the
15、end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Reagents of the American Chemical Society.3Other gradesmay be used, provided it is first ascertained that the reagent isof sufficiently high purity to permit its use
16、without lesseningthe accuracy of the determination.5.2 Unless otherwise indicated, references to water shall beunderstood to mean water conforming to Type I of Specifica-tion D1193. Other reagent water types may be used provided itis first ascertained that the water is of sufficiently high purity to
17、permit its use without adversely affecting the bias and precisionof the test method. Additionally, for those test methodsrequiring water free of CO2, refer to 8.2 of Practice E200.6. Precautions6.1 WarningCarbon dioxide is easily lost from solutionduring transit and storage of samples. It is also po
18、ssible fortotal CO2concentration to increase after sampling due tosolution of finely divided calcium carbonate as a result oftemperature or pressure changes.7. Sampling7.1 Collect the sample in accordance with Practice D1066and Practices D3370, as applicable.7.2 Filter samples when they are collecte
19、d if particulates arepresent that may contain carbonates if dissolved species onlyare to be determined. When aliquots of sample are taken fromsample bottles containing particulates, the bottle must beshaken or otherwise homogenized to ensure a representativesample is taken. When particulates form in
20、 samples due tochanges in temperature, pH, etc., after the sample has beencollected, these particulates must be included in tests of thesample. Care must be used to avoid loss of CO2during anyhomogenization of filtration of samples. Do not filter samplesunless it is required to remove potentially in
21、terfering particu-lates.7.3 Use a hard, glass, chemically resistant bottle for collect-ing the sample.7.4 Fill the sample bottle completely, with no air spaceremaining beneath the cap, and store the sample at a tempera-ture below that at which it was collected until the determinationis made.TEST MET
22、HOD AGAS SENSING ELECTRODETEST METHOD8. Scope8.1 This test method determines total or dissolved carbondioxide (14.3) present as CO2, carbonic acid, bicarbonate ion,and carbonate ion in water, within the interference constraintsspecified.8.2 Samples containing 2 to 800 mg/L total CO2can beanalyzed by
23、 this test method. The concentration range may beextended by dilution of an appropriate aliquot.8.3 Samples should be analyzed immediately. If this is notpossible, preserve by making them slightly alkaline (pHbetween 8 and 9) using carbonate-free NaOH solution andstore them in a tightly capped vesse
24、l. The latter step preventsabsorption of CO2from the air.8.4 The precision and bias were obtained on reagent waterand a water matrix of choice that included natural waters andbrines. It is the responsibility of the analyst to determine theacceptability of this test method for the water being analyze
25、d.9. Summary of Test Method9.1 Carbon dioxide is liberated by acidification of thesample to pH 5.0. The carbon dioxide electrode uses agas-permeable membrane to separate the sample solution fromthe electrode internal solution. Dissolved carbon dioxide in thesample solution diffuses through the membr
26、ane until an equi-librium is reached between the partial pressure of CO2in thesample solution and the CO2in the internal filling solution. Inany given sample, the partial pressure of CO2will be propor-tional to the concentration of CO2. The diffusion of CO2acrossthe membrane affects the concentratio
27、n of hydrogen ions in theinternal filling solution:CO21H2OH11HCO329.2 The hydrogen ion concentration of the internal solutionis measured by the pH electrode located behind the membrane.Since the hydrogen ion concentration is directly related to CO2concentration, the electrode response is Nernstian.9
28、.3 Samples are treated prior to measurement with a buffersolution that sets the pH between 4.8 and 5.2. At this pH,interferences are minimized and the various ionic forms areconverted to CO2(see Section 10).10. Interferences10.1 Volatile weak acids are potential positive electrodeinterferences. Conc
29、entrations of these interfering species thatcause a 10 % error at 44 mg/L CO2or 100 mg/L (as CaCO3)and at pH 4 and 5, are listed below:Interferences, mg/L pH 5 pH 4H2S107NO2(NO2) 161 24HSO3(SO2) 320 (as SO2) 48 (as SO2)HOAc (acetic acid) 372 216HCOOH (formic acid) 1841 34510.2 Samples containing sul
30、fide can be treated with dilutesolutions of potassium dichromate (or the like), since sulfur isnot an interference for this test method. However, it is possiblethat some organic material could be oxidized to CO2by thistreatment, resulting in falsely high results. The suitability of thetest method fo
31、r samples containing sulfide should be deter-mined individually.10.3 Water vapor is a potential electrode interference. Watercan move across the membrane as water vapor, changing the3Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestio
32、ns 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. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D513 162concentration of the inter
33、nal filling solution under the mem-brane. Such changes will be seen as electrode drift. Watervapor transport is not a problem if (1) the total concentration ofdissolved species in solution (Note 1) is approximately equal tothat of the internal filling solution, and (2) electrode andsample temperatur
34、es are the same.NOTE 1The osmotic strength of a solution is related to the totalconcentration of dissolved species in the solution. For example, theosmotic strength of a solution containing 0.1 M hydrochloric acid, 0.1 Macetic acid, and 0.1 M sucrose is determined as follows: Hydrochloric aciddissoc
35、iates to give 0.1 M hydrogen ion and 0.1 M chloride ion. The aceticacid, because of the concentration of free hydrogen ion, is essentiallyundissociated; thus giving 0.1 M of species. Likewise, the concentration ofsucrose species is 0.1 M . Therefore, the total osmotic strength is 0.4osmolar.10.4 Add
36、ition of carbon dioxide buffer (12.1) to samples oflow osmotic strength automatically adjusts them to the correctlevel. Samples with osmotic strength greater than approxi-mately 1 M should be diluted before measurement to avoiddrifting associated with water vapor transport. Dilution shouldnot reduce
37、 the carbon dioxide level below 2.5 mg/L. Sampleswith osmotic strengths above 1 M that cannot be diluted can bemeasured by adjusting the osmotic strength of the internalfilling solution. To adjust the total concentration of dissolvedspecies in the internal filling solution, add 0.425 g of reagent-gr
38、ade NaNO3to 10 mL of internal filling solution.11. Apparatus11.1 pH Meter, with expanded mV scale, or a selective ionmeter.11.2 CO2Gas-Sensing Electrode.411.3 Mixer, magnetic with TFE-fluorocarbon-coated stirringbar or equivalent.12. Reagents and Materials12.1 Buffer SolutionDissolve 294 g of sodium
39、 citrate inapproximately 700 mL of water in a 1-L volumetric flask.Acidify the solution to pH 4.5 with concentrated HCl (approxi-mately 90 mL) and dilute to the mark with water.12.2 Sodium Bicarbonate Solution, Standard (0.1 M)Dissolve 8.40 g of sodium bicarbonate in water and dilute to1L.12.3 Sodiu
40、m Bicarbonate Solution, Standard (0.01 M)Dilute 10.0 mL of sodium bicarbonate standard solution (0.1M) to 100 mL.12.4 Filter PaperPurchase suitable filter paper. Typicallythe filter papers have a pore size of 0.45-m membrane.Material such as fine-textured, acid-washed, ashless paper, orglass fiber p
41、aper are acceptable. The user must first ascertainthat the filter paper is of sufficient purity to use withoutadversely affecting the bias and precision of the test method.13. Calibration and Standardization13.1 Assemble and check the electrode in accordance withthe manufacturers instructions.13.2 D
42、ilute 10 mL of the buffer solution to 100 mL withwater using a volumetric flask. Transfer the contents of theflask to a 150-mL beaker and add a stirring bar. Immerse theelectrode in the solution. Stir at a slow rate using the magneticstirrer.13.3 Using a volumetric pipette, add 0.5 mL of the 0.01 MN
43、aHCO3standard solution and mix slowly.Allow the potentialreading to stabilize (approximately 10 min) and record thepotential (corresponds to 2.2 mg/L CO2or 5.0 mg/L (asCaCO3).13.4 Using a volumetric pipette, add 0.5 mL of the 0.01 MNaHCO3standard solution and mix slowly.Allow the potentialreading to
44、 stabilize (approximately 5 min) and record thepotential (corresponds to 4.4 mg/L CO2or 10.0 mg/L (asCaCO3).13.5 Using a volumetric pipette, add 0.9 mL of the 0.1 MNaHCO3standard solution and mix slowly.Allow the potentialreading to stabilize (approximately 2 min) and record thepotential (correspond
45、s to 43.2 mg/L CO2or 98.1 mg/L (asCaCO3).13.6 Using a volumetric pipette, add 10 mL of the 0.1 MNaHCO3standard solution and mix slowly.Allow the potentialreading to stabilize (approximately 2 min) and record thepotential (corresponds to 433 mg/L CO2or 983 mg/L (asCaCO3).13.7 Follow manufacturer inst
46、ructions for calibratingselective-ion meters with a direct reading of concentrationcapabilities. For pH meters, generate a calibration curve bycreating a calibration curve by plotting potential values (on thelinear scale) versus concentration (on the logarithmic scale) onsemilogarithmic graph paper
47、to obtain a calibration curve. Thecurve may be extended down to 2 mg/L and up to 800 mg/LCO2. Commercially available meters may be used.14. Procedure14.1 Bring samples to the same temperature as the electrodeand standards.14.2 Place a known volume, Vs, (100 mL is convenient) ofsample in 150-mL beake
48、r and stir slowly. Immerse the elec-trode in the solution.14.3 Add 1 mL of buffer, Vb, for each 10 mL of sample.Allow the potential reading to stabilize and record the value.Read the concentration measured, Cm, directly from the cali-bration curve.14.4 Determine the sample concentration, Cs, as foll
49、ows:Cs5 CmVs1VbVs15. Precision and Bias515.1 PrecisionThe overall and single operator precision ofthis test method, within its designated range, varies with the4There are currently several manufacturers of the gas-sensing electrodes forcarbon dioxide.5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D19-1069. ContactASTM CustomerService at serviceastm.org.D513 163quantity tested as shown in Fig. 1 for reagent water and Fig. 2for selected water matrices. These matrices included naturalwaters
