ASTM D1126-17 Standard Test Method for Hardness in Water.pdf

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1、Designation: D1126 17Standard Test Method forHardness in Water1This standard is issued under the fixed designation D1126; 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 parentheses indicates

2、the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This test method covers the determination of hardness inwater by titration. This

3、 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; the upper limitcan be extended to all concentrations by sample dilution. It ispossible to d

4、ifferentiate 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 the testmethod for waters of untested matrices.1.3 The values stated in SI units are to b

5、e regarded asstandard. No other units of measurement are included in thisstandard.1.4 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, health, and environmental

6、 practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guid

7、es and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision

8、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 Methods for Water Analysis3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard,

9、refer toTerminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 equivalent per million (epm), na unit chemicalequivalent weight of solute per million unit weights of solu-tion.3.2.2 laboratory control sample (LCS), na solution withcertified hardness.4. Summary of Test Method4.1 Ca

10、lcium and magnesium ions in water are sequesteredby the addition of disodium ethylenediamine tetraacetate. Theend 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

11、 Use5.1 Hardness salts in water, notably calcium andmagnesium, are the primary cause of tube and pipe scaling,which frequently causes failures and loss of process efficiencydue to clogging or loss of heat transfer, or both.5.2 Hardness is caused by any polyvalent cations, but thoseother than Ca and

12、Mg are seldom present in more than traceamounts. The term hardness was originally applied to water inwhich 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.1

13、This 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 Dec. 1, 2017. Published December 2017. Originallyapproved in 1950. Last previous edition approved in 2012 as D11

14、26 12. DOI:10.1520/D1126-17.2For 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-(1hydroxy-2napththyl)

15、azo-7nitro1 naphthalenesulfonicacid, sodium salt, Color Index 14645.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordanc

16、e with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.16. Interferences6.1 The substances s

17、hown in Table 1 represent the highestconcentrations that have been found not to interfere with thisdetermination.6.2 The test method is not suitable for highly coloredwaters, which obscure the color change of the indicator.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all

18、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 it is first ascertained thatthe reagent is of sufficiently high purity to permit its usew

19、ithout lessening the accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water conformingto Specification D1193, Type I. Other reagent water types maybe used provided it is first ascertained that the water is ofsufficient

20、ly 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 Solution (1+4)Mix 1 volumeof NH4OH (sp gr 0.90) with 4 volumes of water.7.4 Buffer SolutionPr

21、epare 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), and 10 g of potassium sodiumtartrate (KNaC4O64H2O) in 100 mL of water.7.4.3 When cool mix th

22、e 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. Thereagent will be effective for at least 1 month.7.5 Calcium Solution, Standard (1 mL = 0.20 mg C

23、aCO3)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 IndicatorThe hardness indicator can beprepared, stored, and used in liquid or powder form.7.

24、7.1 Hardness Indicator SolutionDissolve 0.5 g ofChrome Black T3in 50 mL of diethanolamine or trietha-nolamine. Store the solution in a dark-colored bottle. Thissolution has a storage life of several months.7.7.2 Hardness Indicator PowderGrind 0.5 g of ChromeBlack T3with 100 g of powdered sodium chlo

25、ride. 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.7.9 Disodium Ethylenediamine Tetraacetate (Na2H2EDTA)Solution, Standard (1 mL = 1.0 mg CaCO3)Dis

26、solve 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 solution using the standard calcium (7.5) solution, and thatprocedure in Section 9 that will be used f

27、or 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 andrestandardize monthly.7.10 Sodium Hydroxide Solution (50 g/L)Dissolve 50 g ofsodium hydroxide in w

28、ater and dilute to 1 L.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the U

29、nited 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 InterferencesSubstanceMaximumConcentrationWithoutInterferencein the Tota

30、lHardnessTest, 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, Cu+20 2Iron, fer

31、ric, 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+10 5Zinc, Zn

32、+20 5ANo data are available.BIron will not interfere in concentrations up to 200 mg/L. However, the red color ofthe end point may return in about 30 s.CManganese will not interfere in concentrations up to 10 mg/L if a few crystals ofK4Fe(CN)63H2O are added to the buffer immediately before use.DAccur

33、ate 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.D1126 1728. Sampling8.1 Collect the sample in accordance with Practice D1066or Practices D3370 as applicable.9. Proce

34、dure9.1 HardnessMeasure 50 mL of clear sample into anopaque white container or a clear colorless container utilizinga white background. Adjust the pH of the sample to 7 to 10 byadding NH4OH (7.3) solution or HCl (7.8) solution. Add 0.5mL of buffer (7.4) solution, and approximately 0.2 g ofhardness (

35、7.7) indicator powder or 2 drops of liquid and stir.Add standard Na2H2EDTA (7.9) solution slowly from a burettewith continuous stirring until the color changes from red toblue. Complete the titration within 5 min after the bufferaddition. If the titration requires more than 20 mL of thetitrating sol

36、ution, dilute the sample and repeat the test.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, add twice the quantity of the reagents asindicated in 9.1.9.3 Calci

37、um HardnessMeasure 50 mL of the sample intoan opaque white container, or a clear colorless containerutilizing a white background. Add 2 mL of NaOH (7.10)solution and stir. Add approximately 0.2 g of calcium (7.6)indicator and stir. Add standard Na2H2EDTA (7.9) solutionslowly from a burette with cont

38、inuous stirring until the colorchanges from red to royal blue. Complete the titration within 5min after the NaOH addition. If the titration requires more than15 mL of the titrating solution, dilute the sample and repeat thetest.10. Calculations10.1 Calculate the hardness, epm, of the sample as follo

39、ws:Hardness, epm 5 20 C/S (1)where:epm = equivalent parts per million; milliequivalents perlitre,C = standard Na2H2EDTA solution added in titratinghardness, mL, andS = sample taken, mL.10.1.1 Calculate the calcium hardness, epm, of the sampleas follows:Calcium hardness, epm 5 20 D/S (2)where:epm = e

40、quivalent parts per million; milliequivalents perlitre,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, epm 5 E 2 F (3)where:epm = equivalent parts per mi

41、llion; milliequivalents perlitre,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 titratinghardness, mL, andS1= sample taken, mL.10.2.1 Calcula

42、te 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 titrating cal-cium hardness, mL, andS1= sample taken, mL.10.2.2 Calculate the magnesium hardness as calcium car-bonate of the sample as fo

43、llows: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 range for 6laboratories, which include a total of

44、6 operators analyzingeach sample on 3 different days may be expressed as follows:So5 0.0047 X10.40 (7)ST5 0.0078 X11.80 (8)where:So= pooled single-operator precision, mg/L,St= overall precision, mg/L, andX = hardness concentration, mg/L.11.2 The single operator and overall precision of the cal-cium

45、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 X10.37 (9)St5 0.025 X10.61 (10)where:So= pooled single-operator precision, mg/LSt= overall precision, mg/L, andX =

46、calcium hardness concentration, mg/L.6Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D19-1125. ContactASTM CustomerService at serviceastm.org.D1126 17311.3 Recoveries of known amounts of hardness and calciumhardness in a series

47、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 theanalysts responsibility to ensure the validity of this testmethod for waters of untested matrices.11.5 Precision and bias for this test method conforms toPractic

48、e D2777 77, which was in place at the time ofcollaborative testing. Under the allowances made in 1.4 ofPractice D2777 13, these precision and bias data do meetexisting requirements for interlaboratory studies of CommitteeD19 test methods.12. Quality Control (QC)12.1 To ensure that analytical values

49、obtained using thesetest methods are valid and accurate within the confidence limitsof the test, the following QC procedures must be followed.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 frequency of 10 %. It isrecommended, but not required, to use a second source ifpossible and practi