ASTM D511-2008 Standard Test Methods for Calcium and Magnesium In Water.pdf

1、Designation: D 511 08Standard Test Methods forCalcium and Magnesium In Water1This standard is issued under the fixed designation D 511; 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 parenthe

2、ses indicates 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 Department of Defense.1. Scope1.1 These test methods cover the determination of calciumand magnesium in wa

3、ter by complexometric titration andatomic absorption spectrometric procedures. Two test methodsare included, as follows:SectionsTest Method AComplexometric Titration 7 to 14Test Method BAtomic Absorption Spectrometric 15 to 231.2 The values stated in SI units are to be regarded asstandard. No other

4、units of measurement are included in thisstandard.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 r

5、egulatory limitations prior to use. Specific hazardstatements are given in 12.2.6 and 20.6.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committ

6、ee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 4691 Practice for Measuring Elements in Water by FlameAtomic Absorption SpectrophotometryD 4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD 5810 Guide for Spiking into

7、 Aqueous SamplesD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminology3.1 DefinitionsFor definitions of terms used in these testmethods, refer to Terminology D 1129.4. Significance and Use4.1 Calcium and magnesium salts in water are the p

8、rimarycomponents of water hardness which can cause pipe or tubescaling.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 AnalyticalReagents of the American Ch

9、emical Society.3Other gradesmay be used, provided it is first ascertained that the reagent isof sufficiently high purity to permit its use without lesseningthe accuracy of the determination.5.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water co

10、nformingto Specification D 1193, Type 1, II, or III water. Type I ispreferred and more commonly used. Type II water wasspecified at the time of round-robin testing of these testmethods.NOTE 1The user must ensure the type of reagent water is sufficientlyfree of interferences. The water should be anal

11、yzed using this test method.6. Sampling6.1 Collect the sample in accordance with Practices D 3370.6.2 If total recoverable calcium and magnesium concentra-tions are being determined, acidify the water sample withHNO3(sp gr 1.42) to a pH of 2 or less immediately at the timeof collection; normally abo

12、ut 2 mL/L are required. The holdingtime for the samples may be calculated in accordance withPractice D 4841.1These 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

13、 Oct. 1, 2008. Published November 2008. Originallyapproved in 1937. Last previous edition approved in 2003 as D 511 03.2For 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

14、to the standards Document Summary page onthe ASTM website.3Reagent 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 L

15、td., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.3 If dissolved calcium and magnesium conce

16、ntrations arebeing determined, filter the samples through a 0.45-m mem-brane filter and acidify with HNO3(sp gr 1.42) to a pH of 2 orless immediately at time of collection; normally about 2 mL/Lare required.6.4 A number of sources of calcium contamination havebeen encountered in laboratories.Among t

17、he most common areplastic ware, paper towels, and dust. Rinsing plastic ware withsample prior to use, avoiding contact of apparatus with papertowels, and keeping exposure to the air to a minimum will limitthe possibility of contamination.TEST METHOD ACOMPLEXOMETRICTITRATION7. Scope7.1 This test meth

18、od is applicable to most waters in a rangefrom 1 to 1000 mg/L of calcium plus magnesium expressed ascalcium, but may fail in the analysis of highly colored waters,brines, or waters that contain excessive amounts of metals. Theupper and lower limits may be extended by either dilution oruse of micro a

19、pparatus.7.2 Data are not available to determine which matrices wereused to obtain the precision and bias data, and it is theresponsibility of the analyst to determine the acceptability ofthis test method for the matrix being analyzed.8. Summary of Test Method8.1 EDTA (ethylenediamine tetraacetic ac

20、id or its salts) isadded to a sample containing calcium and magnesium ionsafter the pH of the solution is adjusted to 10 for the determi-nation of calcium and magnesium or from pH 12 to 13 for thedetermination of calcium alone. The EDTA initially complexesthe calcium and then the magnesium. The end

21、point is observedby the use of a suitable indicator. At a pH of 12 to 13magnesium is precipitated. Magnesium is determined by thedifference between an aliquot titrated at pH 10 and one titratedat pH 12 to 13.9. Interferences9.1 EDTA reacts with iron, manganese, copper, zinc, lead,cobalt, nickel, bar

22、ium, strontium, calcium, magnesium, andseveral other metals. The interference of heavy metals isminimized by the addition of hydroxylamine and cyanide,which reduce or complex the metals, or both. Metal concen-trations as high as 5 mg/L of iron, 10 mg/L of manganese, 10mg/L of copper, 10 mg/L of zinc

23、, and 10 mg/L of lead can betolerated when hydroxylamine and cyanide are added.9.2 In the titration of calcium plus magnesium, the higheroxidation states of manganese above Mn+2react rapidly withthe indicator to form discolored oxidation products. Hydroxy-lamine hydrochloride reagent is used to redu

24、ce manganese tothe divalent state. The divalent manganese interference can beeliminated by addition of one or two small crystals of potas-sium ferrocyanide.9.2.1 Orthophosphate and sulfate ions interfere at concen-trations in excess of 500 and 10 000 mg/L, respectively.9.2.2 In the presence of alumi

25、num concentrations in excessof 10 mg/L, the blue color that indicates that the end point hasbeen reached will appear and then, on short standing, willrevert to red. The reversion should not be confused with thegradual change that normally takes place in the titrated sampleseveral minutes after the t

26、itration has been completed.9.3 In the titration of calcium, ammonium purpurate reactswith strontium but not with magnesium or barium. However,the end point in the presence of strontium is sluggish, and thetitration is not strictly stoichiometric. Barium does not titrate ascalcium, but affects the i

27、ndicator in some unknown way so thatno end point, or at best a poor end point, is obtained. Bariumcan be removed by prior precipitation with sulfuric acid, butcare must be exercised to prevent precipitation of calcium.Orthophosphate will precipitate calcium at the pH of the test.9.4 A possible inter

28、ference from the commonly used poly-phosphates, organic phosphonates, and EDTA/NTA com-pounds in water treatment should be recognized.10. Apparatus10.1 Titration AssemblySome analysts prefer to use con-ventional lighting and hand stirring. Others report better resultsby using a visual-titration asse

29、mbly consisting of a motor-driven stirrer, 25-mL burette, white-porcelain-base buretteholder, and shaded incandescent lamp. The sample beaker isplaced near the front of the porcelain base and the reaction isviewed diagonally downward through the side of the beakerand against the white background. Il

30、lumination is from behindthe beaker. The capacity of the burette, type lighting, andbackground color may be varied depending on the ionicconcentrations normally encountered and the indicator chosen.10.2 pH Meter, with expanded mV scale.11. Reagents11.1 Buffer Solution, Ammonium Chloride-AmmoniumHydr

31、oxideDissolve 67.6 g of ammonium chloride (NH4Cl)in 200 mL of water. Add 570 mL of concentrated ammoniumhydroxide (NH4OH, sp gr 0.900). Add 5.00 g of magnesiumsalt of EDTA and dilute to 1000 mL. Store in a tightlystoppered plastic bottle to prevent the loss of ammonia.Discard the solution when 1 mL

32、added to a neutralized samplefails to produce a pH of 10.0 6 0.1 at the titration end point.To attain highest accuracy, adjust the magnesium level to exactequivalence through the appropriate addition of a small amountof either disodium EDTA or magnesium sulfate (MgSO4).11.2 Calcium Indicator Solutio

33、n:11.2.1 Ammonium PurpurateMix thoroughly 1.0 g ofammonium purpurate with 200 g of sucrose. Place in a bottleprovided with a dispensing spoon of 0.2-g capacity.11.2.2 Fluorescein Methylene Iminodiacetic Acid4Grind0.2 g of fluorescein methylene iminodiacetic acid and 0.12 g ofthymolphthalein with 20

34、g of potassium chloride to 40 to 50mesh size. Place in a bottle provided with a dispensing spoonof 0.2-g capacity.11.3 Calcium Solution, Standard (1.00 mL = 0.400 mgcalcium)Suspend 1.000 g of calcium carbonate (CaCO3),dried at 180C for 1.0 h before weighing, in approximately 6004Calcein, W., Fluoros

35、cein Complexon, and Fluorexon, supplied by variouscommercial firms, have been found satisfactory for this purpose.D511082mL of water and dissolve cautiously with a minimum of diluteHCl. Dilute to 1000 mL with water in a volumetric flask.11.3.1 Alternatively, certified calcium stock solutions arecomm

36、ercially available through chemical supply vendors andmay be used.11.4 Chrome Black T Solution (4.0 g/L)Dissolve 0.4 g ofChrome Black T in 100 mL of water. This solution has a shelflife of approximately 1 week. Alternatively, a dry powdermixture composed of 0.5 g of dye and 100 g of powderedsodium c

37、hloride may be used. Store this in a dark-coloredbottle provided with a dispensing spoon of approximately 0.2-gcapacity. The shelf life is at least 1 year.NOTE 2Chrome Black T is also known as Eriochrome Black T.11.5 EDTA Solution, Standard (0.01 M, 1 mL = 0.401 mgcalcium or 0.243 mg manganese)Disso

38、lve 3.72 g ofNa2EDTA dihydrate, which has been dried overnight overH2SO4in a desiccator, in water (or at 80C. for 1 hour) anddilute to 1000 mL in a volumetric flask. The reagent is stablefor several weeks. Check the titer of the reagent by titrating25.00 mL of CaCO3standard solution as described in

39、theprocedure for sample analysis.11.6 Hydroxylamine Hydrochloride Solution (30 g/L)Dissolve 30 g of hydroxylamine hydrochloride (NH2OHHCl)in water and dilute to 1000 mL.11.7 Potassium Ferrocyanide(K4Fe(CN)63H2O).11.8 Sodium Cyanide Solution (25 g/L)Dissolve 25 g ofsodium cyanide (NaCN) in water and

40、dilute to 1000 mL.Warning: Sodium cyanide is a deadly poison. Do not addNaCN to any acid solution or acidify any solution containing it.Use this reagent in a fume hood.11.9 Sodium Hydroxide Solution (80 g/L or 2 M)Dissolve80 g of sodium hydroxide (NaOH) in 800 mL of water. Cooland dilute to 1000 mL.

41、11.9.1 Alternatively, a commercially prepared solution ofsodium hydroxide is available through chemical supply ven-dors and may be used.12. Procedure12.1 Calcium Plus Magnesium:12.1.1 Measure 100.0 mL of a well-mixed acidified sample(see 6.2) into a 125-mL beaker or flask.NOTE 3If only dissolved cal

42、cium plus magnesium is to be deter-mined, omit 12.1.1 through 12.1.4 and proceed to 12.1.5.12.1.2 Add 5 mL of hydrochloric acid (HCl, sp gr 1.19) toeach sample.12.1.3 Heat the samples on a steambath or hot plate until thevolume has been reduced to 15 to 20 mL, making certain thatthe samples do not b

43、oil.NOTE 4For samples with high levels of dissolved or suspendedmatter, the amount of reduction in volume is left to the discretion of theanalyst.12.1.4 Cool and filter the samples through a suitable filter(such as fine-textured, acid-washed, ashless paper) into100-mL volumetric flasks. Wash the pap

44、er two or three timeswith water and bring to the volume.12.1.5 Measure 50 mL of the filtered sample (50.00-mLmaximum) into a 150-mL beaker and adjust the volume toapproximately 50 mL.Adjust the pH to 7 to 10 by the dropwiseaddition of ammonium hydroxide (NH4OH, sp gr 0.900).NOTE 5For analysis of bri

45、nes an appropriate aliquot size often can bedetermined from knowledge of the specific gravity, for example:1.000 to 1.025, use 25 mL1.025 to 1.050, use 10 mL1.050 to 1.090, use 5 mL1.090 to 1.120, use 1 mL1.120 to 1.180, use 0.1 mL12.1.6 Insert the beaker in the titration assembly and startthe stirr

46、er.12.1.7 Add 1 mL of NH2OHHCl solution (11.6).12.1.8 Add 1 mL of buffer solution (11.1). Measure the pHand verify that it falls in the pH range from 10.0 + 0.1. Adjustby the dropwise addition of ammonium hydroxide.12.1.9 Add 2 mL of NaCN solution (11.8) Warning:Sodium cyanide is a deadly poison. Do

47、 not add NaCN to anyacid solution or acidify any solution containing it. Use thisreagent in a fume hood.12.1.10 If manganese is present, add one or two smallcrystals K4Fe(CN)63H2O(11.7).12.1.11 Add 4 to 5 drops of Chrome Black T indicatorsolution (11.4). If powdered indicator is used add approxi-mat

48、ely 0.2 g.12.1.12 Titrate with standard EDTA solution (11.5) untilblue or purple swirls begin to show. The end point is reachedwhen all traces of red and purple have disappeared and thesolution is pure blue in color. The titration should be completedwithin 5 min of the buffer addition. If more than

49、15 mL oftitrant is required, take a smaller sample aliquot and repeat thetest.12.1.13 Record the volume of EDTA solution required totitrate calcium plus magnesium.12.1.14 Determine a reagent blank correction by similarlytitrating 50 mL of water including all added reagents.12.2 Calcium:12.2.1 Refill the burette with EDTA standard solution(11.5).12.2.2 Pipette another aliquot of the same sample (50.00 mLmaximum) into a 150-mL beaker and adjust the volume toapproximately 50 mL (see Note 5).12.2.3 Insert the beaker in the titration assembly and startthe stirr