ASTM D1126-17 Método Estantar para Medicion de La Dureza en Agua

 

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

 

Designation: D1126 − 17

Standard Test Method for

Hardness in Water1 This standard is issued under the fixed designation D1126; the number immediately following the designation indicates the year of  original origin al adoption or, in the case of revis revision, ion, the year of last revision. revision. A number in paren parenthese thesess indicates the year of last reappr reapproval. oval. A superscript 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. Sco Scope* pe* 1.1 This test method covers covers the determination determination of hardness hardness in water by titration. This test method is applicable to waters that are clear in appearance and free of chemicals that will complex calcium or magnesium. The lower detection limit of this test method is approximat approximately ely 2 to 5 mg/L as CaCO3; the upper limit can be extended to all concentrations by sample dilution. It is possible to differentiate between hardness due to calcium ions and that due to magnesium ions by this test method. 1.2 This test method was tested on reagent water only. only. It is thee us th user er’s ’s re resp spon onsi sibi bilit lity y to en ensu sure re th thee va valid lidity ity of th thee tes testt method for waters of untested matrices. 1.3 1. 3 Th Thee va valu lues es sta stated ted in SI un units its are to be re rega gard rded ed as standard. No other units of measurement are included in this standard. 1.4   This standar standard d doe doess not purport purport to add addre ress ss all of the safetyy co safet conc ncer erns ns,, if an anyy, as asso socia ciate ted d wi with th its us use. e. It is th thee responsibility of the user of this standard to establish appro priate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5   This int intern ernati ationa onall sta standa ndard rd was dev develo eloped ped in acc accor or-dance with internationally recognized principles on standardizatio iza tion n es esta tabl blis ishe hed d in th thee De Decis cisio ion n on Pr Prin incip ciple less fo forr th thee  Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical  Barriers to Trade (TBT) Committee. 2. Referenc Referenced ed Documents Documents 2.1   ASTM Standards:2 D1066 Practice D1066  Practice for Sampling Steam D1129 Terminology D1129  Terminology Relating to Water D1193   Specification for Reagent Water D1193 1

This test method is under the juris jurisdictio diction n of ASTM Committee Committee D19  on Water and is the direct responsibility of Subcommittee D19.05 Subcommittee  D19.05   on Inorganic Constituents in Water. Current edition approved Dec. 1, 2017. Published December 2017. Originally approved in 1950. Last previous edition approved in 2012 as D1126 – 12. DOI: 10.1520/D1126-17. 2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [email protected]. For  Annual Book of ASTM  Standards volume information, refer to the standard’s Document Summary page on the ASTM website.

D2777 Practice for Determination of Precision and Bias of  D2777 Practice Applicable Test Methods of Committee D19 on Water D3370 Practices D3370  Practices for Sampling Water from Closed Conduits D5847  Practic D5847 Practicee for Wri Writing ting Quality Control Specific Specifications ations for Standard Test Methods for Water Analysis 3. Terminology 3.1   Definitions: 3.1.1 For definitions definitions of terms used in this standard, refer to Terminology  D1129  D1129.. 3.2  Definitions of Terms Specific to This Standard: 3.2.1   equi equiva valen lentt pe perr mi mill llio ion n (e (epm pm), ), n— a un unit it ch chemi emica call equivalent weight of solute per million unit weights of solution. 3.2.2   laboratory control sample (LCS), n— a solution with certified hardness. 4. Summ Summary ary of Test Test Method 4.1 Calcium and magnesium magnesium ions in water are sequestered by the addition of disodium ethylenediamine tetraacetate. The end point of the reaction is detected by means of Chrome Black  T3, wh whic ich h ha hass a re red d co colo lorr in th thee pr pres esen ence ce of ca calci lcium um an and d magnesium and a blue color when they are sequestered. 5. Signi Significanc ficancee and Use 5.1 5. 1 Har Hardn dnes esss sa salt ltss in wa wate terr, no nota tabl bly y ca calc lciu ium m an and d magnesium, are the primary cause of tube and pipe scaling, which frequently causes failures and loss of process efficiency due to clogging or loss of heat transfer, or both. 5.2 Hardn Hardness ess is caused by any polyv polyvalent alent cations, cations, but those other than Ca and Mg are seldom present in more than trace amounts. The term hardness was originally applied to water in which whi ch it was hard to was wash; h; it ref referr erred ed to the soap-was soap-wastin ting g properties prop erties of water water.. Wit With h most normal alkalin alkalinee water water,, these soap-wastin soapwasting g prop properties erties are directl directly y related to the calcium and magnesium content.

3

3–Hydroxy–4-(1–hydroxy-2–na 3–Hydroxy–4-( 1–hydroxy-2–napththyl) pththyl) azo-7–nitro– azo-7–nitro–1 1 naphthalene naphthalenesulfonic sulfonic

acid, sodium salt, Color Index 14645.

*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

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D1126 − 17 TABLE 1 Freedom of Reaction from Interferences Maximum Concentration Without Interference in the Total Hardness Test, mg/L

Substance

Aluminum, Al+ + + Ammonium, NH4 + Bicarbonate, HCO3 Bromine, Br

20   −

Cadmium, Cd+ + Carbonate, CO3 − − Chloride, Cl− Chlorine, Cl Chromate, CrO4 − − Cobalt,, Co   + + Cobalt Copper, Cu   + + Iron, ferric, Fe   + ++ Iron, ferrous, Fe   + + Lead, Pb   ++ Manganese, Mn   + + Nickel, Ni   + + Nitrate, NO3 − Nitrite, NO2 − Phosphate, PO4 − − Silicate, SiO3 − − Strontium, Sr   + + Sulfate, SO4 − − Sulfite, SO3 − − Tannin, Quebracho

−

 

Maximum Concentration Without Interference in the Calcium Hardness Test, mg/L

... ...

5 2 000 500 2

20 1 000 10 000 ... 500 0.3 20 10B  10B  20 1C  0.5D  500 500 100 200

... 50 ... 2 500 ... 2 20 20 5 10C  ... 500 500 ... 100

A

E

E 

10 000 500 200

10 000 500 50

10 10 20

5 5 5

7.2  Purity of Water— Unless Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to Specification D1193 Specification  D1193,,  Type I. Other reagent water types may be us used ed pr prov ovid ided ed it is fir first st as ascer certai taine ned d th that at th thee wa wate terr is of  suffficie suf icientl ntly y hig high h pur purity ity to per permit mit its use wit withou houtt adv advers ersely ely affec af fectin ting g the pre precisi cision on and bias of the tes testt met method hod.. Type II water was specified at the time of round robin testing of this test method. 7.3   Ammonium Hydroxide Solution  (1 + 4) — Mix Mix 1 volume of NH4OH (sp gr 0.90) with 4 volumes of water. 7.4   Buffer Buffer Solut Solution—  ion— Pre Prepar paree the buf buffer fer sol solutio ution n in thr three ee steps as follows: 7 . 4. 1 D is s o l ve 40 g of sodium t et r ab o r a te (Na2B4O7·10H2O) in 800 mL of water. 7.4.2 Dissol Dissolve ve 10 g of sodium hydroxid hydroxidee (NaOH), 10 g of  sodium sulfide (Na2S·9H2O), and 10 g of potassium sodium tartratee (KNaC4O6·4H2O) in 100 mL of water. tartrat 7.4. 7. 4.3 3 Wh When en co cool ol mix th thee tw two o so solu lutio tions ns an and d ad add d 1 g of  magnesium magne sium disod disodium ium ethyle ethylenediam nediamine ine tetraac tetraacetate, etate, havin having g a magnesium-to magne sium-to-EDT -EDTA A mole ratio of 1 to 1. Make up to 1 L with water. Keep the solution bottle stoppered when not in use. The reagent will be effective for at least 1 month. 7.5  Calcium Solution, Standard  (1  (1 mL = 0.20 mg CaCO3) — 

  + +++

Tin, stannic, Sn   + Tin, stannous, Sn Zinc, Zn   ++

+

A

No data are available. B  Iron will not interfere in concentrations up to 200 mg/L. However, the red color of the end point may return in about 30 s. C  Manganese will not interfere in concentrations up to 10 mg/L if a few crystals of K4Fe(CN)6·3H2O are added to the buffer immediately before use. D  Accurate results can be obtained in the presence of 1 mg/L nickel, but the end point is slow under these conditions. E  If strontium is present, it will be titrated with calcium and magnesium.

6. Interfere Interferences nces 6.1 The substances substances shown in  in   Table 1 represent 1  represent the highest concentrations that have been found not to interfere with this determination. 6.2 6. 2 Th Thee te test st me meth thod od is no nott su suita itabl blee fo forr hi high ghly ly co colo lore red d waters, which obscure the color change of the indicator. 7. Reag Reagents ents 7.1   Purity of Reagents— Reagent Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analyt Analytical ical Reagents of the America American n Chemical Society. Society.4 Other grades may be used, provided it is first ascertained that thee re th reag agen entt is of su sufffici icien ently tly hi high gh pu puri rity ty to pe perm rmit it its us usee without lessening the accuracy of the determination.

4

American an  Reagent Chemicals, American Chemical Society Specifications, Americ

Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by the American American Chemi Chemical cal Society, Society, see  Annual Standa Standards rds for Labor Laboratory atory Chemicals,  BDH Ltd., Poole, Dorset, U.K., and the   United States Pharmacopeia and National Formulary,  U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.

Dissolve 0.2000 g of CaCO3 in 3 to 5 mL of HCl (1 + 4). Dilute Dilute to 1 L with water. 7.6   Calcium Indica Indicator—  tor— Use powder powdered ed hydro hydroxynaph xynaphthol thol 5 blue, or grind solid hydroxynaphthol blue to 40 to 50 mesh size. 7.7   Hardness Hardness Indica Indicator—  tor— The T he ha hard rdne ness ss in indi dica cato torr can be prepared, stored, and used in liquid or powder form. 7.7.1   Har Diss ssol olve ve 0. 0.5 5 g of  Hardness dness Indic Indicator ator Solut Solution—  ion— Di 3 Chrome Chr ome Black T in 50 mL of di diet etha hano nolam lamin inee or tr triet ietha ha-nolamin nol amine. e. Sto Store re the sol solutio ution n in a dar dark-c k-colo olored red bot bottle. tle. This solution has a storage life of several months. 7.7.2   Hardness Indicator Powder— Grind Grind 0.5 g of Chrome Black Blac k T3 wit with h 100 g of powdered powdered sodium sodium chl chlori oride. de. Use a dark-colored bottle for storage. The powder has a storage life of at least 1 year. 7.8   Hydrochloric Acid  (1 + 4) — Mix M ix 1 volume of concentrated hydrochloric acid (sp gr 1.19) with 4 volumes of water. 7.9   Disodium Ethylenediamine Tetraacetate (Na2 H 2  EDTA) Solution, Standard  (1  (1 mL = 1.0 mg CaCO 3) — Dissolve Dissolve 3.8 g of  disodium disod ium ethyle ethylenediam nediamine ine tetraac tetraacetate etate dihyd dihydrate rate in appro approxiximately 800 mL of water. Adjust the pH of the solution to 10.5 with NaOH solution (50 g/L). Determine the concentration of  this solution using the standard calcium (7.5 (7.5)) solution, and that procedure in Section 9 Section  9 that  that will be used for the sample analysis (9.1 9.1,,  9.2  9.2,, or or 9.3  9.3). ). Adjust the concentration of the EDTA so that 1 mL will be equivalent equivalent to 1.0 mg of CaCO3. Store the standard EDTA EDT A in pol polyet yethyl hylene ene,, plas plastic, tic, or har hard d rub rubber ber bot bottles tles and restandardize monthly. 7.10  Sodium Hydroxide Solution (50 g/L) — Dissolve Dissolve 50 g of  sodium hydroxide in water and dilute to 1 L. 5 3–Hydroxy-4 (2–hydroxy–4 sulfo–1 naphthyl) azo–2, 7–naphthalenedisulfonic acid, trisodium salt.

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D1126 − 17

8. Samp Sampling ling 8.1 Collect the sample in accordance accordance with Practice D1066 Practice D1066 or Practices D3370 Practices  D3370 as  as applicable. 9. Pro Procedu cedure re 9.1   Hardness— Meas M easur uree 50 mL of cle clear ar sa samp mple le in into to an opaque white container or a clear colorless container utilizing a white background. Adjust the pH of the sample to 7 to 10 by

where: epm ep m = equi equiva valen lentt pa part rtss pe perr mil millio lion; n; mil millie liequ quiv ivale alent ntss pe perr litre,  E    = hardness hardness,, epm epm,, and F    = calcium hardn hardness, ess, epm. 10.2 Calc 10.2 Calcula ulate te the har hardne dness ss as calc calcium ium car carbon bonate ate of the sample as follows: S 1 Hardness, mg/L as CaCO 3 5 1000  C 1 / S 

 

(4 )

adding NH4OH (7.3 7.3)) solution or HCl   (7.8 7.8)) solution. Add 0.5 mL of bu bufffe ferr   (7.4 7.4))   solut solutio ion, n, an and d ap appr prox oxim imate ately ly 0. 0.2 2 g of  hardness   (7.7 hardness 7.7))   indicator powder or 2 drops of liquid and stir. Add standard Na2H2EDT EDTA A (7.9 7.9)) solution slowly from a burette with continuous stirring until the color changes from red to blue bl ue.. Co Comp mplet letee th thee ti titra tratio tion n wi with thin in 5 mi min n af after ter th thee bu bufffe ferr addi ad ditio tion. n. If th thee ti titra tratio tion n re requ quir ires es mo more re th than an 20 mL of th thee titrating solution, dilute the sample and repeat the test.

where: C 1   = st stan anda dard rd Na2H2EDT EDTA A sol soluti ution on add added ed in titr titratin ating g hardness, mL, and sample ple tak taken, en, mL. S 1   = sam

9.2   Low Hardness— Determine Determine low-hardness values (0.5 to 5.0 ppm as CaCO 3) in accordance with 9.1 with  9.1,,  but use a 100 mL sample and titrate by means of micro-burette. When employing a 100-mL sample, add twice the quantity of the reagents as indicated in 9.1 in  9.1..

where: standard rd Na2H2EDTA solution added in titrating cal D1   = standa cium hardness, mL, and S 1   = sam sample ple tak taken, en, mL.

9.3   Calcium Hardness— Measure Measure 50 mL of the sample into an opaq op aque ue white wh ite ba cont co ntain ainer er,nd. , or a dcl clear colo co lorl rles esssOH cont co ntain ainer er) utili ut ilizi zing ng a wh white ite back ckgr grou ound . Ad Add 2earmL of NaOH Na (7.10 7.10) solution and stir. Add approximately 0.2 g of calcium (7.6 ( 7.6)) indicat ind icator or and stir stir.. Add stan standar dard d Na2H2EDTA (7.9 (7.9))   solution slowly from a burette with continuous stirring until the color changes from red to royal blue. Complete the titration within 5 min after the NaOH addition. If the titration requires more than 15 mL of the titratin titrating g solution, dilute the sample and repeat the test. 10. Calc Calculati ulations ons

10.2.1 10.2. 1 Calculat Calculatee the calcium hardness hardness as calcium carbonate carbonate of the sample as follows: S 1 Calcium Calciu m hardn hardness, ess, mg/L as CaCO3 5 1000 D 1 / S 

 

Magnesium hardness, mg/L as CaCO3 5 G 2  H 

11.1 The single operation 11.1 operation and overall precision precision of the total hard ha rdne ness ss te test st me meth thod od wi with thin in it itss de desi sign gnat ated ed ra rang ngee fo forr 6 labora lab orator tories, ies, whi which ch inc includ ludee a tot total al of 6 ope operato rators rs ana analyz lyzing ing each sample on 3 different days may be expressed as follows: S o 5 0.0047 X 1 0.40

(7)

S T  5 0.0078 X 1 1.80

(8)

where:

epm ep m = equi equiva vale lent nt pa part rtss pe perr mi milli llion on;; mil millie liequ quiv ivale alent ntss pe perr litre, standa dard rd Na Na2H2EDT EDTA A sol solutio ution n add added ed in titr titratin ating g C    = stan hardness, mL, and S    = sam sample ple tak taken, en, mL.

S o   = pooled single single-oper -operator ator precisio precision, n, mg/L, mg/L, overalll precisio precision, n, mg/L, and S t    = overal hardness concen concentration tration,, mg/L.  X    = hardness

 

10.1.2 10.1 .2 Calcul Calculate ate th thee ma magn gnes esiu ium m ha hard rdne ness ss,, ep epm, m, of th thee sample as follows: Magnesium hardness, epm 5  E  2 F 

11.2 11 .2 The single operator operator and ove overall rall precisio precision n of the calcium hardness test method within its designated range for 6 labora lab orator tories, ies, whi which ch inc includ ludee a tot total al of 6 ope operato rators rs ana analyz lyzing ing each sample on 3 different days may be expressed as follows: S o 5 0.0052 X 1 0.37

(2 )

where: epm ep m = equi equiva vale lent nt pa part rtss pe perr mi milli llion on;; mil millie liequ quiv ivale alent ntss pe perr litre,  D   = stan standa dard rd Na Na2H2EDT EDTA A sol solutio ution n add added ed in titr titratin ating g calcium hardness, mL, and sample ple tak taken en for test test,, mL. S    = sam

 

(3 )

(6 )

11. Pre Precisi cision on and Bias6

where:

S  Calcium hardness, epm 5 20 D / S 

 

where: G   = hardne hardness, ss, mg/ mg/L L as CaCO3, and  H    = calc calcium ium har hardne dness, ss, mg/ mg/L L as CaCO CaCO3.

(1 )

10.1.1 10.1. 1 Calcula Calculate te the calcium hardness, hardness, epm, of the sample as follows:

(5 )

10.2.2 Calculat 10.2.2 Calculatee the magnesium hardness hardness as calcium carbonate of the sample as follows:

10.1 Calculat Calculatee the hardness, epm, of the sample as follows: follows: Hardness, Hardn ess, epm 5 20  C  /   / S  S 

 

S t  5 0.025 X 1 0.61

(9) (10)

where: S o   = pooled single single-oper -operator ator precisio precision, n, mg/L   = overall overal l precisio p recision, n, mg/L, and S t  hardness ess concen concentration tration,, mg/L. mg/L.  X    = calcium hardn

6

Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D19-1125. Contact ASTM Customer Service at [email protected].

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D1126 − 17 TABLE 2 Statistical Information, Total Hardness

12. Quali Quality ty Control Control (QC)

Amount Added, mg/L

Amount Found, mg/L

Bias

% Bias

11.0 45.0 206. 450.

11.4 46.3 206. 453.

+ 0.4 + 1.3 0.0 + 3.

+ 3.6 + 2.9 0.0 + 0.7

No No No No

6.2 25.0 125. 250.

6.1 24.9 126. 250.

Calcium Hardness −0.1 −0.1 + 1.0 0.0

−1.6 −0.4 + 0.8 0.0

No No No No

 

Statistically Significant

11.3 Recoveries of known amounts of hardness and calcium hard ha rdne ness ss in a se seri ries es of pr prep epar ared ed sta stand ndar ards ds fo forr th thee sa same me laboratories and operators are as shown in  Table 2. 2. 11. 1.4 4 These These da data ta ap appl ply y to re reag agen entt wa water ter on only ly.. It is the the analyst’ analy st’ss re resp spon onsi sibi bilit lity y to en ensu sure re th thee va valid lidit ity y of th this is tes testt method for waters of untested matrices. 11.5 Pre Precisi cision on and bias for this tes testt meth method od conforms conforms to Practice   D2777  D2777   – 77 77,, wh whic ich h wa wass in pla lace ce at th thee ti time me of  collabo coll aborati rative ve test testing ing.. Und Under er the allo allowan wances ces mad madee in 1.4 of  Practice   D2777  D2777   – 13, these precision and bias data do meet existing requirements for interlaboratory studies of Committee D19 test methods.

12.1 To ensure that analyti analytical cal values obtained using these test methods are valid and accurate within the confidence limits of the test, the following QC procedures must be followed. 12.2 A ch 12.2 check eck sta stand ndar ard d sh shall all be an analy alyzed zed at a mi mini nimu mum m frequency of 10 % throughout the batch analysis. The value of  the check standard shall fall between 80 % and 120 % of the true value. 12.3 A Laboratory Laboratory Control Control Sample shall be analyze analyzed d with each batch of samples at a minimum frequency of 10 %. It is recomm rec ommend ended, ed, but not required, required, to use a sec second ond source source if  possible and practical for the LCS. 12.4 If th 12.4 thee QC fo forr th thee sa samp mple le ba batc tch h is no nott wi with thin in th thee established establi shed control limits, reana reanalyze lyze the samples or qualif qualify y the results with the appropriate flags, or both (Practice D5847 (Practice  D5847)). 12.5 Blind 12.5 Blind co cont ntro roll sam sampl ples es sh shou ould ld be subm submitt itted ed by an outsid out sidee age agency ncy in ord order er to det determ ermine ine the lab labora orator tory y per perfor for-mance capabilities. 13. Keyw Keywords ords 13.1 analys analysis; is; calcium carbonate carbonate hard hardness; ness; hardness; titration; water

SUMMARY OF CHANGES Committ Comm ittee ee D1 D19 9 ha hass id iden enti tified fied th thee lo loca catio tion n of sel select ected ed ch chan ange gess to th this is st stan anda dard rd sin since ce th thee las lastt is issu suee (D1126 – 12) that may impact the use of this standard. (Approved Dec. 1, 2017.) (1)  Updated  Updated 3.1  3.1  to the current format.

 

(2)  Revised Section  Section   12 12..

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