ASTM D511-2014 Standard Test Methods for Calcium and Magnesium In Water《水中钙镁离子的标准试验方法》.pdf

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1、Designation: D511 14Standard Test Methods forCalcium and Magnesium In Water1This standard is issued under the fixed designation D511; 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 parenthese

2、s 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 U.S. Department of Defense.1. Scope*1.1 These test methods cover the determination of calciumand magnesium i

3、n water by complexometric titration andatomic absorption spectrometric procedures. Two test methodsare included, as follows:SectionsTest Method AComplexometric Titration 715Test Method BAtomic Absorption Spectrometric 16251.2 The values stated in SI units are to be regarded asstandard. The values gi

4、ven in parentheses are mathematicalconversion to inch-pound units that are provided for informa-tion only and are not considered standard.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

5、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 Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777

6、Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD4691 Practice for Measuring Elements in Water by FlameAtomic Absorption SpectrophotometryD4841 Practice for Estimation of Holding Time for Water

7、Samples Containing Organic and Inorganic ConstituentsD5810 Guide for Spiking into Aqueous SamplesD5847 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

8、D1129.4. 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 chemicals shall be used in all tests.Unless otherwise indicated, it is intended that all reagents shallconform

9、to the specifications of the Committee on AnalyticalReagents of the American Chemical 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 other

10、wise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D1193, 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 o

11、f 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 D3370.6.2 If total recoverable calcium and magnesium concentra-tions are being determined, acidify the water sample withHNO3(sp gr

12、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 D4841.1These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Su

13、bcommittee D19.05 on InorganicConstituents in Water.Current edition approved Oct. 1, 2014. Published November 2014. Originallyapproved in 1937. Last previous edition approved in 2009 as D511 09. DOI:10.1520/D0511-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM

14、 Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer 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 reagent

15、s notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.*A Summary of Changes section appears at the end of this stand

16、ardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1NOTE 2Alternatively, the pH may be adjusted in the laboratory if thesample is returned within 14 days. However, acid must be added at least24 hours before analysis to dissolve any met

17、als that adsorb to the containerwalls. This could reduce hazards of working with acids in the field whenappropriate.6.3 If dissolved 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 im

18、mediately at time of collection; normally about 2 mL/Lare required.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 pap

19、ertowels, and keeping exposure to the air to a minimum will limitthe 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

20、 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 apparatus.7.2 Data are not available to determine which matrices wereused to obtain the precision and bias data, and it is theresponsibility

21、of the analyst to determine the acceptability ofthis test method 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-nat

22、ion 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 point is observedby the use of a suitable indicator. At a pH of 12 to 13magnesium is precipitated. Magnesium is determined by thedifference

23、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, barium, strontium, calcium, magnesium, andseveral other metals. The interference of heavy metals isminimized by the addition of hydroxylamine a

24、nd 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, and 10 mg/L of lead can betolerated when hydroxylamine and cyanide are added.9.2 In the titration of calcium plus magnesium, the higheroxi

25、dation states of manganese above Mn+2react rapidly withthe indicator to form discolored oxidation products. Hydrox-ylamine 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-si

26、um 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 aluminum concentrations in excessof 10 mg/L, the blue color that indicates that the end point hasbeen reached will appear and then, on short stan

27、ding, willrevert to red. The reversion should not be confused 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. Howev

28、er,the end point in the presence of strontium is sluggish, and 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

29、 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 interference from the commonly usedpolyphosphates, organic phosphonates, and EDTA/NTA com-pounds in water treatment should be recognized.10. Appa

30、ratus10.1 Titration AssemblySome analysts prefer to use con-ventional lighting and hand stirring. Others report better resultsby using a visual-titration assembly consisting of a motor-driven stirrer, 25-mL burette, white-porcelain-base buretteholder, and shaded incandescent lamp. The sample beaker

31、isplaced near the front of the porcelain base and the reaction isviewed diagonally downward through the side of the beakerand against the white background. Illumination is from behindthe beaker. The capacity of the burette, type lighting, andbackground color may be varied depending on the ionicconce

32、ntrations normally encountered and the indicator chosen.10.2 pH Meter, with expanded mV scale.11. Reagents and Materials11.1 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

33、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 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 t

34、he magnesium level to exactequivalence through the appropriate addition of a small amountof either disodium EDTA 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 dis

35、pensing spoon of 0.2-g capacity.D511 14211.2.2 Fluorescein Methylene Iminodiacetic Acid4Grind0.2 g of fluorescein methylene 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 C

36、alcium 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 600mL of water and dissolve cautiously with a minimum of diluteHCl. Dilute to 1000 mL with water in a volumetric flask.11.3.1 Alternatively, cer

37、tified calcium stock solutions ofappropriate known purity are commercially available throughchemical supply vendors and may 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 po

38、wdermixture composed of 0.5 g of dye and 100 g of powderedsodium chloride 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 3Chrome Black T is also known as Eriochrome Black T.11.5 EDTA Solution, St

39、andard (0.01 M, 1 mL = 0.401 mgcalcium or 0.243 mg magnesium)Dissolve 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 reage

40、nt by titrating25.00 mL of CaCO3standard solution as described in 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 So

41、lution (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 reagent in a fume hood.)11.9 Sodium Hydroxide Solution (80 g/L or 2 M)Dissolve80 g of sodi

42、um hydroxide (NaOH) in 800 mL of water. Cooland dilute to 1000 mL.11.9.1 Alternatively, a commercially prepared solution ofsodium hydroxide of appropriate known purity is availablethrough chemical supply vendors and may be used.11.10 Filter PaperPurchase suitable filter paper. Typicallythe filter pa

43、pers have a pore size of 0.45-m membrane.Material such as fine-textured, acid-washed, ashless paper, orglass fiber paper are acceptable. The user must first ascertainthat the filter paper is of sufficient purity to use withoutadversely affecting the bias and precision of the test method.12. Procedur

44、e12.1 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 4If only dissolved calcium plus magnesium is to bedetermined, 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) toea

45、ch 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 5For samples with high levels of dissolved or suspendedmatter, the amount of reduction in volume is left to the discretion of theanalyst.12.1

46、.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 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

47、the volume toapproximately 50 mL.Adjust the pH to 7 to 10 by the dropwiseaddition of ammonium hydroxide (NH4OH, sp gr 0.900).NOTE 6For analysis of brines 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, us

48、e 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 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

49、10.0 + 0.1. Adjustby the dropwise addition of ammonium hydroxide.12.1.9 Add 2 mL of NaCN solution (11.8). (WarningSodium cyanide is a deadly poison. Do 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-mately 0.2 g.12.1.12 Titrate with standard EDTA solution (11.5) untilblue or purple swirls begin to show.