1、Designation: D513 111Standard 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.1NOTEThis Test Method was changed editorially in 2012.1. Scope*1.1 These test methods cover the measurement of total ordissolved carbon dioxide present a
3、s carbon dioxide (CO2),carbonic acid, bicarbonate ion, and carbonate ion in water:Range SectionsTest Method A (Gas Sensing Electrode) 2 to 800 mg/L 8 to 15Test Method B (CO2Evolution, CoulometricTitration)5to800mg/L 16to241.2 Carbon dioxide may also be detected from carbonatespresent in particulates
4、 in samples.1.3 Test Method A is applicable to various 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.
5、1.6 Several test methods were discontinued from this 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 the
6、safety concerns, if 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.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling
7、SteamD1129 Terminology Relating to WaterD1193 Specification 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 Q
8、uality Control Specificationsfor Standard Test Methods for Water AnalysisE200 Practice for Preparation, Standardization, and Storageof Standard and Reagent Solutions for Chemical Analysis3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods, refer to Terminology D1129.4. Si
9、gnificance and Use4.1 Carbon dioxide is a major respiration product of plantsand animals 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
10、 mineral decom-position; however, underground water, particularly deep wa-ters, 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 sys
11、tem can disturb the carbonate equilibrium andresult in calcite 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. Rec
12、arbonation of municipal supplies duringfinal stages of softening 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 spe
13、cifications of the Committee on Analytical1These test methods 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 Dec. 15, 2006. Published February 2012. Originallyapproved in 193
14、8. Last previous edition approved in 2011 as D513 11. DOI:10.1520/D0513-11e01.2For 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 on
15、the ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Reagents of the American Chemical Society.3Other gradesmay be used, provided it is first ascertained t
16、hat the reagent isof sufficiently high purity to permit its use 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 fi
17、rst ascertained that the water is of sufficiently high purity topermit 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 f
18、rom solutionduring transit and storage of samples. It is also possible 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 Practices D1066and D3370,
19、as applicable.7.2 Filter samples when they are collected 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 r
20、epresentativesample is taken. When particulates form in 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 filte
21、r samplesunless it is required to remove potentially interfering 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 i
22、t was collected until the determinationis made.TEST METHOD 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 Samp
23、les containing 2 to 800 mg/L total CO2can beanalyzed by 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-fre
24、e NaOH solution andstore them in a tightly capped vessel. 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 theaccept
25、ability of this test method for the water being analyzed.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 d
26、ioxide in thesample solution diffuses through the membrane 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 diff
27、usion of CO2acrossthe membrane affects the concentration of hydrogen ions in theinternal filling solution:CO21 H2OH11 HCO329.2 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 t
28、o CO2concentration, the electrode response is Nernstian.9.3 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
29、acids are potential positive electrodeinterferences. Concentrations 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 2
30、16HCOOH (formic acid) 1841 34510.2 Samples containing sulfide 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 f
31、alsely high results. The suitability of thetest method for 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 theconcentration of the internal filling solution under the mem-
32、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 temperatures are the same.3Reagent Chemicals,
33、 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 For
34、mulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D513 1112NOTE 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
35、 sucrose is determined as follows: Hydrochloric aciddissociates 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. The
36、refore, the total osmotic strength is 0.4osmolar.10.4 Addition 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 associa
37、ted with water vapor transport. Dilution shouldnot reduce 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
38、 the internal filling solution, add 0.425 g of reagent-grade 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. Reagents1
39、2.1 Buffer SolutionDissolve 294 g of sodium 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 bica
40、rbonate in water and dilute to1L.12.3 Sodium Bicarbonate Solution, Standard (0.01 M)Dilute 10.0 mL of sodium bicarbonate standard solution (0.1M) to 100 mL.13. Calibration and Standardization13.1 Assemble and check the electrode in accordance withthe manufacturers instructions.13.2 Dilute 10 mL of t
41、he 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 MNaHCO3standard so
42、lution 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 stabilize (appr
43、oximately 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 (corresponds to 43.2 mg/L C
44、O2or 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 Plot potential values (on the linear sca
45、le) versusconcentration (on the logarithmic scale) on semilogarithmicgraph paper to obtain a calibration curve. The curve may beextended down to 2 mg/L and up to 800 mg/L CO2. Commer-cially available meters may be used.14. Procedure14.1 Bring samples to the same temperature as the electrodeand stand
46、ards.14.2 Place a known volume, Vs, (100 mL is convenient) ofsample in 150-mL beaker 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, direct
47、ly from the cali-bration curve.14.4 Determine the sample concentration, Cs, as follows:Cs5 CmVs1 VbVs15. Precision and Bias515.1 PrecisionThe overall and single operator precisionof this test method, within its designated range, varies with thequantity tested as shown in Fig. 1 for reagent water and
48、 Fig. 2for selected water matrices. These matrices included naturalwaters and brines.15.2 BiasRecoveries of known amounts of total CO2from reagent water and selected water matrices were as shownin Table 1.15.3 The information in 15.1 and 15.2 is derived fromround-robin testing in which eight laborat
49、ories, includingtwelve independent operators, participated. Of twelve data setsranked as described in Practice D2777, four were rejected inthe case of reagent water and three were rejected in the case ofselected water matrices. Four outlier data points were alsorejected. Four sample levels were run on three days, and blankswere obtained for the waters used.15.4 Precision and bias for this test method conforms toPractice D2777-77, which was in place at the time of collab-orative testing. Under the allowances made in 1.4 of PracticeD2777-08, these precision and
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