DIN 38406-3-2002 German standard methods for the examination of water waste water and sludge - Cations (group E) - Part 3 Determination of calcium and magnesium complexometric meth.pdf

1、ICS 13.060.50Deutsche Einheitsverfahren zur Wasser-, Abwasser- undSchlammuntersuchung; Kationen (Gruppe E) Teil 3: Bestimmungvon Calcium und Magnesium, komplexometrisches Verfahren (E 3)In keeping with current practice in standards published by the International Organization for Standardization(ISO)

2、, a comma has been used throughout as the decimal marker.Ref. No. DIN 38406-3 : 2002-03English price group 07 Sales No. 010708.03DEUTSCHE NORM March 200238406-3Continued on pages 2 to 7. No part of this translation may be reproduced without the prior permission ofDIN Deutsches Institut fr Normung e.

3、V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).German standard methods for the examination of water, waste water and sludgeCations (group E)Determination of calcium and magnesium by complexometrictitration (E 3)Translation by DI

4、N-Sprachendienst.In case of doubt, the German-language original should be consulted as the authoritative text.ContentsPageForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Scope . . . . . . . . . . . . . . . . . . . . . . . .

5、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Determination of calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Determination o

6、f total calcium and magnesium . . . . . . . . . . . . . . . . . . . . . . 45 Calculation of magnesium content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Explanatory notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7This sta

7、ndard, togetherwith DIN EN ISO 7980,July 2000 edition,supersedes DIN 38406-3,September 1982 edition.ForewordThis standard has been jointly prepared by the Normenausschuss Wasserwesen (Water Practice StandardsCommittee) and Study Group Wasserchemie (Water Chemistry) of the Gesellschaft Deutscher Chem

8、iker(German Chemists Society) (cf. Explanatory notes).Expert assistance and specialized laboratories will be required to perform the analyses specified in thisstandard. Existing safety instructions shall be observed.Depending on the objective of the analysis, a check shall be made on a case-by-case

9、basis as to whetherand to what extent additional boundary conditions will have to be specified.AmendmentsThis standard differs from the September 1982 edition in that the method of determining calcium andmagnesium by atomic absorption spectrometry has been incorporated in DIN EN ISO 7980 and thecomp

10、lexometric method (not incorporated in DIN EN ISO 7980) has been editorially revised.Previous editionDIN 38406-3: 1982-09.CAUTION. Users of this standard should be familiar with standard laboratory practice. It is notclaimed that all the safety problems associated with the use of the method have bee

11、n dealt withexhaustively here. It is therefore the responsibility of the user to take appropriate safety precautionsand to ensure that these comply with national regulations.Page 2DIN 38406-3 : 2002-031 ScopeThis standard specifies two methods of determining calcium and magnesium.The method describe

12、d in clause 3 serves to determine calcium in ground water, surface water and drinkingwater in concentrations of 2 mg/l to 100 mg/l (equivalent to 0,05 mmol/l to 2,5 mmol/l). In the case of highercalcium concentrations, the sample is to be diluted prior to analysis. The method may also be applied to

13、wastewater provided its heavy metal concentrations do not give rise to interference.The method described in clause 4 serves to determine the total calcium and magnesium in ground water,surface water and drinking water if their total concentration exceeds 0,05 mmol/l. The method shall not be usedfor

14、seawater, water having a comparable salt content and waste water. Other methods, such as the atomicabsorption spectrometric method specified in DIN EN ISO 7980, are suitable in such cases.To determine calcium and magnesium separately, it will first be necessary to determine the calcium content bythe

15、 method specified in clause 3 and then calculate the magnesium content from the difference between thetotal calcium and magnesium concentration and the calcium concentration (see clause 5).2 Normative referencesThis standard incorporates, by dated or undated reference, provisions from other publicat

16、ions. These norma-tive references are cited at the appropriate places in the text, and the titles of the publications are listed below.For dated references, subsequent amendments to or revisions of any of these publications apply to thisstandard only when incorporated in it by amendment or revision.

17、 For undated references, the latest edition ofthe publication referred to applies.DIN 12691 Class AS fast delivery one-mark bulb pipettes, with a waiting time of 15 seconds, forlaboratory useDIN 12695 Classes A and B graduated pipettes for partial delivery, for laboratory useDIN 12700-3 Burettes fit

18、ted with offset burette stopcock with tail, for laboratory useDIN EN 25667-1 Water quality Sampling Part 1: Guidance on design of sampling programs(ISO 5667-1 : 1980)DIN EN 25667-2 Water quality Sampling Part 2: Guidance on sampling techniques (ISO 5667-2 : 1991)DIN EN ISO 1042 Laboratory glassware

19、One-mark volumetric flasks (ISO 1042 : 1998)DIN EN ISO 5667-3 Water quality Sampling Part 3: Guidance on the preservation and handling of samples(ISO 5667-3 : 1994)DIN EN ISO 7980 Water quality Determination of calcium and magnesium Atomic absorptionspectrometric method (ISO 7980 : 1986)DIN EN ISO 8

20、655-4 Piston-operated volumetric apparatus Part 4: Diluters (ISO 8655-4 : 2002)ISO 1773 : 1997 Laboratory glassware Narrow-necked boiling flasks3 Determination of calcium3.1 PrincipleWhen calcium ions are titrated with an aqueous solution of the disodium salt of ethylenedinitrilotetraacetic acid(EDT

21、A) using calconcarboxylic acid as indicator at a pH value of between 12 and 13, they form a red complex.Magnesium ions are precipitated as hydroxide and do not interfere with the determination.During the titration, free calcium ions are the first to react with the EDTA, followed by those bound to th

22、eindicator, which changes colour from red to blue.3.2 InterferenceAluminium, barium, lead, iron, copper, manganese, strontium, zinc and tin ions may interfere with the determi-nation by also being included in the titration result or rendering the colour change indistinct. At the high pH valueof the

23、titration, orthophosphate ions in concentrations greater than 1 mg/l cause calcium to be lost by precipi-tation. Interference due to carbonate ions can be prevented by boiling the sample and then cooling it to about50 C.Interference by iron in concentrations of 10 mg/l or above can be eliminated by

24、adding 250 mg of sodiumcyanide (Caution. Highly toxic!) or a few ml of triethanolamine immediately prior to titration. In addition, cyanideions reduce interference due to zinc, copper and cobalt, while triethanolamine reduces interference due toaluminium.Calcium carbonate may be precipitated if the

25、titration is performed too slowly or if the calcium ion concentrationexceeds 100 mg/l (equivalent to 2,5 mmol/l). To prevent this, titrate the sample more quickly or dilute it.Page 3DIN 38406-3 : 2002-033.3 DesignationDesignation of the method of determining calcium (E 3) as specified in this standa

26、rd, using standard EDTAsolution as titrant and calconcarboxylic acid as indicator (2):Method DIN 38406 E 3-23.4 ApparatusThe following equipment shall be used.3.4.1 Volumetric flasks, of nominal capacities 50 ml and 100 ml (e.g. ISO 1042 A 50 C volumetric flasks).3.4.2 Conical flasks, of nominal cap

27、acities 250 ml and 500 ml (e.g. conical flasks as in ISO 1773).3.4.3 Diluters, as in DIN EN ISO 8655-4, or burette, of nominal capacity 25 ml(e.g. DIN 12700-3 SGA 25 005 burette).3.4.4 One-mark bulb pipettes, of nominal capacities 2 ml, 20 ml and 50 ml (e.g. DIN 12691 VPAS 2 pipettes).3.4.5 Magnetic

28、 stirrer.3.4.6 Magnetic follower, PTFE*)-coated.3.5 Reagents3.5.1 GeneralOnly analytical grade reagents shall be used and the water used shall be distilled or water of equivalent purity.The following reagents shall be used.3.5.2 2 mol/l sodium hydroxide solution, NaOH, prepared by dissolving 8 g of

29、sodium hydroxide in 100 mlof water.Ensure that the solution remains low in carbonate by keeping it in a polyethylene flask and excluding air as faras possible.3.5.3 0,01 mol/l standard EDTA solution, prepared by dissolving 3,725 g of the dihydrate of the disodiumsalt of ethylenediaminotetraacetic ac

30、id, C10H14N2O8Na2. 2H2O, dried to constant mass at 80 C, in water ina 1000 ml volumetric flask and making up to the mark.Commercially available, ready-to-use standard EDTA solutions or those prepared by diluting suitable concen-trates may be used provided the shelf life information is observed.3.5.4

31、 Calconcarboxylic acid indicator, prepared by carefully mixing 0,2 g of calconcarboxylic acid,C21H14N2O7S . 3H2O, with 100 g of sodium chloride, NaCl.Instead of calconcarboxylic acid, calcein (sodium salt of fluorescein-2,7-bis(methyleniminodiacetic acid) maybe used.3.5.5 Triethanolamine, N(CH2CH2OH

32、)3.3.5.6 Sodium cyanide, NaCN.3.6 Sampling and sample preparationThe water samples, to be collected as specified in DIN EN 25667-1, DIN EN 25667-2 and DIN EN ISO 5667-3,shall contain between 2 mg/l and 100 mg/l of calcium. If a calcium concentration is expected to exceed100 mg/l, dilute an aliquot o

33、f the sample to 50 ml to obtain the required concentration range. If the calciumconcentration is less than 2 mg/l, take a larger sample volume.Samples preserved by acidification shall be neutralized with sodium hydroxide solution.3.7 ProcedurePipette 50 ml of water sample into a 250 ml conical flask

34、, add 2 ml of sodium hydroxide solution and about0,2 g of calconcarboxylic acid indicator and titrate immediately, using the magnetic stirrer to continuously stirthe solution being titrated. The end point is indicated by a distinct change in colour from red to blue. No furtherchange in colour shall

35、occur when a further drop of standard EDTA solution is added.Automatic titrators may be used and the end point detected using suitable ion-selective electrodes.*) Polytetrafluoroethylene.Page 4DIN 38406-3 : 2002-033.8 EvaluationCalculate the concentration by mass of calcium, r(Ca), in mg/l, using eq

36、uation (1) and the amount-of-substanceconcentration of calcium, c(Ca), in mmol/l, using equation (2):r(Ca) = G50G45G45G2CG56G66G63G56 G2EG2EG2E G30G38G34G30(1)c(Ca) = G30G38G34G30G28G43G61G29G2CG72(2)whereVEis the volume of standard EDTA solution required for titration, in ml;VPis the volume of wate

37、r sample taken, in ml;cEis the amount-of-substance concentration of the standard EDTA solution, in mol/l;40,08 is the molar mass of calcium, in mg/mmol;f is a conversion factor (here, f = 1000 mmol/mol).3.9 Expression of resultAll results are subject to a degree of uncertainty, this often being grea

38、test for lower concentrations. In individualcases, the uncertainty can be estimated from laboratory quality control data (e.g. range control cards forduplicate determinations), another method being interlaboratory testing. The uncertainty of measurement mayvary considerably with the type of sample.T

39、he concentrations shall be reported to an accuracy of 1 mg/l.EXAMPLE:Calcium (Ca2+): 58 mg/l3.10 Test reportThe test report shall refer to this standard and include the following details:a) designation of method;b) identification of water sample;c) expression of result, as specified in subclause 3.9

40、;d) sample pretreatment, if any;e) any deviation from this method and an indication of any circumstances that may have affected the result.4 Determination of total calcium and magnesium4.1 PrincipleWhen calcium and magnesium ions are titrated complexometrically with the disodium salt of ethylene-dia

41、minotetraacetic acid (EDTA) using eriochrome black T as indicator at a pH value of 10, free calcium andmagnesium ions are the first to react with the EDTA, followed by those bound to the indicator, which changescolour from reddish violet to blue.4.2 InterferenceAluminium, barium, lead, iron, copper,

42、 manganese, strontium, zinc and tin ions may interfere with the determi-nation by also being included in the titration result or by adversely affecting the colour change. At the high pHvalue of the titration, orthophosphate ions in concentrations greater than 1 mg/l cause calcium to be lost byprecip

43、itation.Interference due to carbonate ions can be eliminated by boiling the sample and then cooling it to about 50 C.Interference due to iron in concentrations of 10 mg/l and above can be prevented by adding 250 mg of sodiumcyanide (Caution. Highly toxic!).Samples that contain interfering amounts of

44、 the ions referred to may be analysed, for example, by the methodspecified in DIN EN ISO 7980.4.3 DesignationDesignation of the method of determining total calcium and magnesium (E 3) as specified in this standard, usingstandard EDTA solution as titrant and eriochrome black T as indicator (3):Method

45、 DIN 38406 E 3-3Page 5DIN 38406-3 : 2002-034.4 ApparatusThe following equipment shall be used.4.4.1 Volumetric flasks, of nominal capacities 50 ml, 100 ml and 1000 ml (e.g. ISO 1042 A50 C volumetricflasks).4.4.2 Conical flasks, of nominal capacities 250 ml and 500 ml (e.g. conical flasks as in ISO 1

46、773).4.4.3 Diluters (e.g. as in DIN EN ISO 8655-4), or burette, of nominal capacity 25 ml(e.g. DIN 12700-3 SGA 25 005 burette).4.4.4 One-mark bulb pipettes, of nominal capacities 20 ml and 50 ml (e.g. DIN 12691 VPAS 20 pipettes).4.4.5 Graduated pipette, of nominal capacity 5 ml (e.g. DIN 12695 MPAT

47、5 005 pipette).4.4.6 Magnetic stirrer.4.4.7 Magnetic follower, PTFE-coated.4.5 Reagents4.5.1 GeneralOnly analytical grade reagents shall be used and the water used shall be distilled water or water of equivalentpurity.The following reagents shall be used.4.5.2 0,01 mol/l standard EDTA solution, prep

48、ared as described in subclause 3.5.3.4.5.3 Eriochrome black T indicator, prepared by dissolving 0,5 g of eriochrome black T (sodium 1-(1-hy-droxy-2-naphthylazo)-6-nitro-2-naphthol-4-sulfonate) in 100 ml of triethanolamine.NOTE: To render the colour change sharper, 0,17 g of metanilic acid (sodium 4-

49、anilidoazobenzene-3-sulfonate)may be added to the solution. This causes the colour to change from red to green via pale grey.4.5.4 Buffer solution, with a pH value of 10, prepared by dissolving 67,5 g of ammonium chloride, NH4Cl, in570 ml of 0,91 g/ml ammonia solution, NH3, in a 1000 ml volumetric flask, adding 0,5 g of EDTA disodiummagnesium salt, C10H12N2O8Na2Mg, and making the solution up to the mark with water.Store the solution in a polyethylene flask. If 10 ml of the solution are diluted to 100 ml with water, the pH valuewill be