ASTM D511-2003 Standard Test Methods for Calcium and Magnesium In Water《水中钙镁离子的标准测试方法》.pdf

1、Designation: D 511 03Standard 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 (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.1. Scope*1.1 These test methods cover the determination of calciumand magnesium in

3、water 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 This standard does not purport to address all of thesafety concerns,

4、 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. Specific hazardstatements are given in 12.2.6 and 20.6.2. Referenced Documents2.1 ASTM

5、 Standards:D 1129 Terminology Relating to Water2D 1193 Specification for Reagent Water2D 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D19 on Water2D 3370 Practices for Sampling Water from Closed Con-duits2D 4691 Practice for Measuring Elements in Water by F

6、lameAtomic Absorption Spectrophotometry2D 4841 Practice for Estimation of Holding Times for WaterSamples Containing Organic and Inorganic Constituents2D 5810 Guide for Spiking Into Aqueous Samples2D 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3

7、3. 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 primarycomponents of water hardness which can cause pipe or tubescaling.5. Purity of Reagents5.1 Reagent grade chemical

8、s 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 Chemical Society.4Other gradesmay be used, provided it is first ascertained that the reagent isof sufficiently high puri

9、ty 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 conformingto Specification D 1193, Type 1, II, or III water. Type I ispreferred and more commonly used. Type II water wa

10、sspecified 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 analyzed using this test method.6. Sampling6.1 Collect the sample in accordance with Practices D 3370.6.2 If total recover

11、able 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 about 2 mL/L are required. The holdingtime for the samples may be calculated in accordance withPractice D 4841.6.3 If dis

12、solved calcium and magnesium concentrations 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.1These test methods are under the jurisdiction of ASTM Comm

13、ittee D19 onWater and are the direct responsibility of Subcommittee D19.05 on InorganicConstituents in Water.Current edition approved June 10, 2003. Published July 2003. Originallyapproved in 1937. Last previous edition approved in 1998 as D 511 93 (1998).2Annual Book of ASTM Standards, Vol 11.01.3A

14、nnual Book of ASTM Standards, Vol 11.02.4Reagent 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

15、, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.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 St

16、ates.6.4 A number of sources of calcium contamination havebeen encountered in laboratories.Among the 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 li

17、mitthe possibility of contamination.TEST METHOD ACOMPLEXOMETRICTITRATION7. Scope7.1 This test method 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 excessiv

18、e amounts of metals. Theupper and lower limits may be extended by either dilution oruse of micro apparatus.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 meth

19、od for the matrix being analyzed.8. Summary of Test Method8.1 EDTA (ethylenediamine tetraacetic acid 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 thedeterm

20、ination of calcium alone. The EDTA initially complexesthe calcium and then the magnesium. The end 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

21、to 13.9. Interferences9.1 EDTA reacts with iron, manganese, copper, zinc, lead,cobalt, nickel, barium, 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

22、concen-trations as high as 5 mg/L of iron, 10 mg/L of manganese, 10mg/L of copper, 10 mg/L of zinc, 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 ind

23、icator to form discolored oxidation products. Hydroxy-lamine hydrochloride reagent is used to reduce 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 interfer

24、e at concen-trations in excess of 500 and 10 000 mg/L, respectively.9.2.2 In the presence of aluminum 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

25、with thegradual change that normally takes place in the titrated sampleseveral minutes after the titration 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

26、 thetitration is not strictly stoichiometric. Barium does not titrate ascalcium, but affects the indicator 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 precipita

27、tion of calcium.Orthophosphate will precipitate calcium at the pH of the test.9.4 A possible interference 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-

28、ventional lighting and hand stirring. Others report better resultsby using a visual-titration assembly consisting of a motor-driven stirrer, 25-mL buret, white-porcelain-base buret holder,and shaded incandescent lamp. The sample beaker is placednear the front of the porcelain base and the reaction i

29、s vieweddiagonally downward through the side of the beaker andagainst the white background. Illumination is from behind thebeaker. The capacity of the burette, type lighting, and back-ground color may be varied depending on the ionic concentra-tions normally encountered and the indicator chosen.11.

30、Reagents11.1 Buffer Solution, Ammonium Chloride-AmmoniumHydroxideDissolve 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

31、 prevent the loss of ammonia.Discard the solution when 1 mL 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

32、 or magnesium sulfate (MgSO4).11.2 Calcium Indicator Solution: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 Acid5Grind0.2 g of fluorescein methyl

33、ene iminodiacetic acid and 0.12 g ofthymolphthalein with 20 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

34、h before weighing, in approximately 600mL of water and dissolve cautiously with a minimum of diluteHCl. Dilute to 1000 mL with water in a volumetric flask.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.

35、Alternatively, a dry powder5Calcein, W., Fluoroscein Complexon, and Fluorexon, supplied by variouscommercial firms, have been found satisfactory for this purpose.D511032mixture composed of 0.5 g of dye and 100 g of powderedsodium chloride may be used. Store this in a dark-coloredbottle provided with

36、 a dispensing spoon of approximately 0.2-gcapacity. The shelf life is at least 1 year.11.5 EDTA Solution, Standard (0.01 M, 1 mL = 0.401 mgcalcium or 0.243 mg manganese)Dissolve 3.72 g ofNa2EDTA dihydrate, which has been dried overnight overH2SO4in a desiccator, in water and dilute to 1000 mL in avo

37、lumetric flask. The reagent is stable for several weeks.Check the titer of the reagent by titrating 25.00 mL of CaCO3standard solution as described in the procedure for sampleanalysis.11.6 Hydroxylamine Hydrochloride Solution (30 g/L)Dissolve 30 g of hydroxylamine hydrochloride (NH2OHHCl)in water an

38、d 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 dilute to 1000 mL.(WarningSodium cyanide is a deadly poison. Do not addNaCN to any acid solution or acidify any solution containing it.Use this reage

39、nt in a fume hood.)11.9 Sodium Hydroxide Solution (80 g/L)Dissolve 80 g ofsodium hydroxide (NaOH) in 800 mL of water. Cool and diluteto 1000 mL.12. Procedure12.1 Calcium Plus Magnesium:12.1.1 Measure 100.0 mL of a well-mixed acidified sampleinto a 125-mL beaker or flask.NOTE 2If only dissolved calci

40、um plus magnesium is to be deter-mined, omit 12.1.1 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 boil.NOTE 3For sam

41、ples 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 paper two or three t

42、imeswith water and bring to the volume.12.1.5 Pipette the filtered sample (50.00-mL maximum) intoa 150-mL beaker and adjust the volume to approximately 50mL. Adjust the pH to 7 to 10 by the dropwise addition ofammonium hydroxide (NH4OH, sp gr 0.900).NOTE 4For analysis of brines an appropriate aliquo

43、t 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 stirrer.12.1.7 Add 1 mL of NH2

44、OHHCl solution.12.1.8 Add 1 mL of buffer solution. Measure the pH andverify that it falls in the pH range from 10.0 + 0.1.12.1.9 Add 2 mL of NaCN solution (WarningSodiumcyanide is a deadly poison. Do not add NaCN to any acidsolution or acidify any solution containing it. Use this reagentin a fume ho

45、od.)12.1.10 If manganese is present, add one or two smallcrystals K4Fe(CN)63H2O.12.1.11 Add 4 to 5 drops of Chrome Black T indicatorsolution. If powdered indicator is used add approximately 0.2g.12.1.12 Titrate with standard EDTA solution until blue orpurple swirls begin to show. The end point is re

46、ached when alltraces of red and purple have disappeared and the solution isclear blue in color. The titration should be completed within 5min of the buffer addition. If more than 15 mL of titrant isrequired, take a smaller sample aliquot and repeat the test.12.1.13 Record the volume of EDTA solution

47、 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.12.2.2 Pipette another aliquot of the same sample (50.00 mLmaximum) into a 150-

48、mL beaker and adjust the volume toapproximately 50 mL (see Note 4).12.2.3 Insert the beaker in the titration assembly and startthe stirrer.12.2.4 Add 1 mL of NH2OHHCl.12.2.5 Add 1 mL of NaOH solution. The pH should rangefrom 12 to 13.12.2.6 Add 1 mL of NaCN (WarningSodium cyanide isa deadly poison.

49、Do not add NaCN to any acid solution oracidify any solution containing it. Use this reagent in a fumehood.).12.2.7 Add 0.2 g of calcium indicator solution and proceedimmediately with the titration.12.2.8 Titrate with standard EDTA solution to the appropri-ate end point. If ammonium purpurate is used, the end pointwill be indicated by color change from salmon pink to orchidpurple. If fluorescein methylene iminodiacetic acid is used, theend point will be indicated by a color change from deep greento purple. The titration should be completed within 5 min of th