1、Designation: D 1126 02 (Reapproved 2007)e1Standard Test Method forHardness in Water1This standard is issued under the fixed designation D 1126; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.e1NOTEAdded acronym to 3.1.2 and updated 11.5 editorially in August 2007.1.
3、 Scope1.1 This test method covers the determination of hardness inwater by titration. This test method is applicable to waters thatare clear in appearance and free of chemicals that will complexcalcium or magnesium. The lower detection limit of this testmethod is approximately 2 to 5 mg/Las CaCO3; t
4、he upper limitcan be extended to all concentrations by sample dilution. It ispossible to differentiate between hardness due to calcium ionsand that due to magnesium ions by this test method.1.2 This test method was tested on reagent water only. It isthe users responsibility to ensure the validity of
5、 the testmethod for waters of untested matrices.1.3 This standard does not purport to address all of thesafety 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 reg
6、ulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Pr
7、actices for Sampling Water from Closed ConduitsD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminology3.1 Definitions:3.1.1 equivalent per million (epm), na unit chemicalequivalent weight of solute per million unit weights of solu-tion.3.1
8、.2 laboratory control sample (LCS), na solution withcertified hardness.3.1.3 For definitions of other terms used in this test method,refer to Terminology D 1129.4. Summary of Test Method4.1 Calcium and magnesium ions in water are sequesteredby the addition of disodium ethylenediamine tetraacetate. T
9、heend point of the reaction is detected by means of Chrome BlackT3, which has a red color in the presence of calcium andmagnesium and a blue color when they are sequestered.5. Significance and Use5.1 Hardness salts in water, notably calcium and magne-sium, are the primary cause of tube and pipe scal
10、ing, whichfrequently causes failures and loss of process efficiency due toclogging or loss of heat transfer, or both.5.2 Hardness is caused by any polyvalent cations, but thoseother than Ca and Mg are seldom present in more than traceamounts. The term hardness was originally applied to water inwhich
11、 it was hard to wash; it referred to the soap-wastingproperties of water. With most normal alkaline water, thesesoap-wasting properties are directly related to the calcium andmagnesium content.6. Interferences6.1 The substances shown in Table 1 represent the highestconcentrations that have been foun
12、d not to interfere with thisdetermination.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Aug. 1, 2007. Published August 2007. Originallyapproved in 1950. Last
13、 previous edition approved in 2002 as D 1126 02.2For 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.33Hydroxy4-(1
14、hydroxy-2napththyl) azo-7nitro1 naphthalenesulfonicacid, sodium salt, Color Index 14645.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.2 The test method is not suitable for highly coloredwaters, which obscure the color change of t
15、he indicator.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of theAmerican Chemical Society.4Other grades may be used, provided
16、 it is first ascertained thatthe reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water conformingto Specification D 1193, Type I. Other rea
17、gent water types maybe used provided it is first ascertained that the water is ofsufficiently high purity to permit its use without adverselyaffecting the precision and bias of the test method. Type IIwater was specified at the time of round robin testing of thistest method.7.3 Ammonium Hydroxide So
18、lution (1 + 4)Mix 1 volumeof NH4OH (sp gr 0.90) with 4 volumes of water.7.4 Buffer SolutionPrepare the buffer solution in threesteps as follows:7.4.1 Dissolve 40 g of sodium tetraborate(Na2B4O710H2O) in 800 mL of water.7.4.2 Dissolve 10 g of sodium hydroxide (NaOH), 10 g ofsodium sulfide (Na2S9H2O),
19、 and 10 g of potassium sodiumtartrate (KNaC4O64H2O) in 100 mL of water.7.4.3 When cool mix the two solutions and add1gofmagnesium disodium ethylenediamine tetraacetate, having amagnesium-to-EDTA mole ratio of 1 to 1. Make up to 1 L withwater. Keep the solution bottle stoppered when not in use. There
20、agent will be effective for at least 1 month.7.5 Calcium Solution, Standard (1 mL = 0.20 mg CaCO3)Dissolve 0.2000 g of CaCO3in 3 to 5 mLof HCl (1 + 4). Diluteto 1 L with water.7.6 Calcium IndicatorUse powdered hydroxynaphtholblue,5or grind solid hydroxynaphthol blue to 40 to 50 meshsize.7.7 Hardness
21、 IndicatorThe hardness indicator can beprepared, stored, and used in liquid or powder form.7.7.1 Hardness Indicator SolutionDissolve 0.5 g ofChrome Black T3in 50 mL of diethanolamine or triethanola-mine. Store the solution in a dark-colored bottle. This solutionhas a storage life of several months.7
22、.7.2 Hardness Indicator PowderGrind 0.5 g of ChromeBlack T3with 100 g of powdered sodium chloride. Use adark-colored bottle for storage. The powder has a storage lifeof at least 1 year.7.8 Hydrochloric Acid (1 + 4)Mix 1 volume of concen-trated hydrochloric acid (sp gr 1.19) with 4 volumes of water.7
23、.9 Disodium Ethylenediamine Tetraacetate (Na2H2EDTA)Solution, Standard (1 mL = 1.0 mg CaCO3)Dissolve 3.8 g ofdisodium ethylenediamine tetraacetate dihydrate in approxi-mately 800 mL of water. Adjust the pH of the solution to 10.5with NaOH solution (50 g/L). Determine the concentration ofthis solutio
24、n using the standard calcium solution, and thatprocedure in Section 9 that will be used for the sample analysis(9.1, 9.2,or9.3). Adjust the concentration of the EDTA so that1 mLwill be equivalent to 1.0 mg of CaCO3. Store the standardEDTA in polyethylene, plastic, or hard rubber bottles andrestandar
25、dize monthly.7.10 Sodium Hydroxide Solution (50 g/L)Dissolve 50 g ofsodium hydroxide in water and dilute to 1 L.8. Sampling8.1 Collect the sample in accordance with Practice D 1066or Practices D 3370 as applicable.9. Procedure9.1 HardnessMeasure 50 mL of clear sample into anopaque white container or
26、 a clear colorless container utilizing4Reagent 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,
27、U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.53Hydroxy-4 (2hydroxy4 sulfo1 naphthyl) azo2, 7naphthalenedisulfonicacid, trisodium salt.TABLE 1 Freedom of Reaction from InterferencesSubstanceMaximumConcentrationWithoutInterfer
28、encein the TotalHardnessTest, mg/LMaximumConcentrationWithoutInterferencein the CalciumHardnessTest, mg/LAluminum, Al+20 5Ammonium, NH4+ A2 000Bicarbonate, HCO3. 500Bromine, Br . 2Cadmium, Cd+20 .Carbonate, CO31 000 50Chloride, Cl10 000 .Chlorine, Cl . 2Chromate, CrO4500 500Cobalt, Co+0.3 .Copper, C
29、u+20 2Iron, ferric, Fe+10B20Iron, ferrous, Fe+10B20Lead, Pb+20 5Manganese, Mn+1C10CNickel, Ni+0.5D.Nitrate, NO3500 500Nitrite, NO2500 500Phosphate, PO4100 .Silicate, SiO3200 100Strontium, Sr+ EESulfate, SO410 000 10 000Sulfite, SO3500 500Tannin, Quebracho 200 50Tin, stannic, Sn+10 5Tin, stannous, Sn
30、+10 5Zinc, Zn+20 5ANo data are available.BIron will not interfere in concentrations up to 200 mg/L. However, the red colorof the end point may return in about 30 s.CManganese will not interfere in concentrations up to 10 mg/L if a few crystalsof K4Fe(CN)63H2O are added to the buffer immediately befo
31、re use.DAccurate results can be obtained in the presence of 1 mg/L nickel, but the endpoint is slow under these conditions.EIf strontium is present, it will be titrated with calcium and magnesium.D 1126 02 (2007)e12a white background. Adjust the pH of the sample to 7 to 10 byadding NH4OH solution or
32、 HCl solution. Add 0.5 mL of buffersolution, and approximately 0.2 g of hardness indicator powderor 2 drops of liquid and stir. Add standard Na2H2EDTAsolution slowly from a burette with continuous stirring until thecolor changes from red to blue. Complete the titration within 5min after the buffer a
33、ddition. If the titration requires more than20 mL of the titrating solution, dilute the sample and repeat thetest.9.2 Low HardnessDetermine low-hardness values (0.5 to5.0 ppm as CaCO3) in accordance with 9.1, but use a 100 mLsample and titrate by means of micro-burette. When employinga 100-mL sample
34、, add twice the quantity of the reagents asindicated in 9.1.9.3 Calcium HardnessMeasure 50 mL of the sample intoan opaque white container, or a clear colorless containerutilizing a white background. Add 2 mL of NaOH solution andstir.Add approximately 0.2 g of calcium indicator and stir.Addstandard N
35、a2H2EDTA solution slowly from a burette withcontinuous stirring until the color changes from red to royalblue. Complete the titration within 5 min after the NaOHaddition. If the titration requires more than 15 mL of thetitrating solution, dilute the sample and repeat the test.10. Calculations10.1 Ca
36、lculate the hardness, epm, of the sample as follows:Hardness, epm 5 20 C/S (1)where:epm = equivalent parts per million; milliequivalents perliter,C = standard Na2H2EDTA solution added in titratinghardness, mL, andS = sample taken, mL.10.1.1 Calculate the calcium hardness, epm, of the sampleas follow
37、s:Calcium hardness, epm 5 20 D/S (2)where:epm = equivalent parts per million; milliequivalents perliter,D = standard Na2H2EDTA solution added in titratingcalcium hardness, mL, andS = sample taken for test, mL.10.1.2 Calculate the magnesium hardness, epm, of thesample as follows:Magnesium hardness, e
38、pm 5 E 2 F (3)where:epm = equivalent parts per million; milliequivalents perliter,E = hardness, epm, andF = calcium hardness, epm.10.2 Calculate the hardness as calcium carbonate of thesample as follows:Hardness, mg/L as CaCO35 1000 C1/S1(4)where:C1= standard Na2H2EDTA solution added in titratinghar
39、dness, mL, andS1= sample taken, mL.10.2.1 Calculate the calcium hardness as calcium carbonateof the sample as follows:Calcium hardness, mg/L as CaCO35 1000 D1/S1(5)where:D1= standard Na2H2EDTA solution added in titratingcalcium hardness, mL, andS1= sample taken, mL.10.2.2 Calculate the magnesium har
40、dness as calcium car-bonate of the sample as follows:Magnesium hardness, mg/L as CaCO35 G 2 H (6)where:G = hardness, mg/L as CaCO3, andH = calcium hardness, mg/L as CaCO3.11. Precision and Bias611.1 The single operation and overall precision of the totalhardness test method within its designated ran
41、ge for 6 labora-tories, which include a total of 6 operators analyzing eachsample on 3 different days may be expressed as follows:So5 0.0047 X 1 0.40ST5 0.0078 X 1 1.80where:So= pooled single-operator precision, mg/L,St= overall precision, mg/L, andX = hardness concentration, mg/L.11.2 The single op
42、erator and overall precision of the cal-cium hardness test method within its designated range for 6laboratories, which include a total of 6 operators analyzingeach sample on 3 different days may be expressed as follows:So5 0.0052 X 1 0.37St5 0.025 X 1 0.61where:So= pooled single-operator precision,
43、mg/LSt= overall precision, mg/L, andX = calcium hardness concentration, mg/L.11.3 Recoveries of known amounts of hardness and calciumhardness in a series of prepared standards for the samelaboratories and operators are as shown in Table 2.11.4 These data apply to reagent water only. It is theanalyst
44、s responsibility to ensure the validity of this testmethod for waters of untested matrices.11.5 Precision and bias for this test method conforms toPractice D 2777 77, which was in place at the time ofcollaborative testing. Under the allowances made in 1.4 ofD 2777 06, these precision and bias data d
45、o meet existingrequirements for interlaboratory studies of Committee D19 testmethods.6Supporting data are available from ASTM International Headquarters. RequestRR: D19-1125.D 1126 02 (2007)e1312. Quality Control (QC)12.1 The following quality control information is recom-mended for the determinatio
46、n of hardness in water.12.2 A check standard shall be analyzed at a minimumfrequency of 10 % throughout the batch analysis. The value ofthe check standard shall fall between 80 % and 120 % of thetrue value.12.3 A Laboratory Control Sample shall be analyzed witheach batch of samples at a minimum freq
47、uency of 10 %.12.4 If the QC for the sample batch is not within theestablished control limits, reanalyze the samples or qualify theresults with the appropriate flags, or both (Practice D 5847).12.5 Blind control samples should be submitted by anoutside agency in order to determine the laboratory per
48、for-mance capabilities.13. Keywords13.1 analysis; calcium carbonate hardness; hardness; titra-tion; waterASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that
49、 determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideratio
