BS 6337-4-1984 General methods of chemical analysis - Method for determination of chloride ions by potentiometry《通用化学分析方法 第4部分 电位滴定法测定氯离子》.pdf

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1、BRITISH STANDARD CONFIRMED AUGUST 1988 BS 6337-4: 1984 ISO 6227:1982 General methods of chemical analysis Part 4: Method for determination of chloride ions by potentiometry ISO title: Chemical products for industrial use General method for determination of chloride ions Potentiometric method UDC 543

2、.257.1:546.131-128.2BS6337-4:1984 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, was published under the authority ofthe Board of BSI and comesintoeffect on 31January1984 BSI 10-1999 The following BSI references relate to the work on this standar

3、d: Committee reference CIC/- Draft for comment 78/51510 DC ISBN 0 580 13661 2 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Committee (CIC/-) to Panel CIC/-/1/2 upon which the following bodies, together with coopted

4、 members nominated by other BSI Committees, were represented: Chemical Industries Association Ministry of Defence Amendments issued since publication Amd. No. Date of issue CommentsBS6337-4:1984 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Fi

5、eld of application 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Procedure 2 7 Expression of results 4 8 Test report 4 Annex A Example (Electrode pair: silver-calomel) 5 Annex B Methods of mineralization of organic products for the determination of total chlorine 5 Annex C Interferences 5 Annex D Oth

6、er ISO/TC 47 publications relating to determination of chloride ion content by potentiometry 6 Table 3BS6337-4:1984 ii BSI 10-1999 National foreword This Part of BS6337is the fourth of a series of general methods of chemical analysis prepared under the direction of the Chemicals Standards Committee.

7、 It is identical with ISO6227:1982 “Chemical products for industrial use General method for determination of chloride ions Potentiometric method” published by the International Organization for Standardization (ISO). For some years, the UK has participated in the work of Subcommittee1, General metho

8、ds, of Technical Committee47, Chemistry, of ISO. As international agreement is reached on the methods, it is proposed to publish them as Parts of this British Standard. The work of Subcommittee1 on such general methods was motivated by the existence of a multiplicity of methods for the same determin

9、ation, all differing to various degrees, that had been prepared by the ISO/TC47subcommittees, etc., responsible for particular chemical products or groups of products. For this historical reason, unnecessary proliferation of different reagents, apparatus and procedures had been developed. These gene

10、ral methods are intended to reduce such proliferation, as far as is possible. They assume that a suitable test solution of a product to be analysed has been prepared, by a method established in the standard relating to the product concerned, which also gives other specific details such as relevant i

11、nterfering species and how to overcome them, and how the results should be expressed. It is hoped and expected that any committees that wish to revise existing, or prepare new, standards involving an analysis corresponding to the general methods, will do so by no more than cross-references to the ap

12、propriate Parts of this British Standard. Because a general method cannot take into account the properties of all the products to which it may be applied, it should indicate what characteristics the test solution should have in order that the method can be applied to it. The compiler of the product

13、standard should indicate how the test portion is to be treated in order to obtain a test solution with the required characteristics. Moreover, while a general method should include a list of known interferences, together with suggestions by which they can be overcome, the product standard should ind

14、icate what interferences might be expected in a particular product and what action should be taken if they are present so that the general method can be applied to the product concerned. Because no product standard can be expected to foresee all eventualities, the user of the product standard should

15、 check in all cases that the general method will be applicable to a particular material. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identic

16、al with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring t

17、o this standard, they should be read as “Part of this British Standard”. The International Standards listed in Annex D are given for information only. Additional information. With reference to clause4, water complying with BS3978 “Water for laboratory use” is suitable.BS6337-4:1984 BSI 10-1999 iii N

18、OTETextual error. In6.2.3, paragraph7, line5, the spelling of the fifth word should be corrected to “millilitres”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a Br

19、itish Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to6 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will

20、be indicated in the amendment table on the inside front cover.iv blankBS6337-4:1984 BSI 10-1999 1 1 Scope This International Standard specifies a general potentiometric method for the determination of chloride ions in solutions prepared from chemical products for industrial use. The preparation of t

21、he test solution and any modifications to the general procedure should be dealt with in the specific International Standard for the chemical product to which the method is to be applied. 2 Field of application The method is applicable to test solutions having chloride ion concentrations, expressed i

22、n milligrams per litre, of between1and1500. The method may be used to determine the total chlorine contained in chemical products after transforming it, if necessary, into chloride ions by a suitable process. The method has an absolute error, expressed as milligrams of chlorine, of0,1to1mg, accordin

23、g to the concentration of the standard volumetric solution used. Under certain conditions, it is possible to determine bromide and iodide ions either simultaneously or separately. If chloride only is to be determined, bromide and iodide may be eliminated by the method described in Annex C. Cyanides,

24、 sulphides, thiocyanates, ammonium and iron(III) salts affect the determination; it is therefore necessary to eliminate them by suitable processes (see Annex C). 3 Principle Potentiometric titration of the chloride (Cl ) ions with standard volumetric silver nitrate solution in an acid medium and in

25、the presence of acetone, using a silver electrode or a chloride or silver ion-selective electrode (measuring electrode) and a calomel or a mercury(I) sulphate electrode (reference electrode). Other electrode pairs have been recommended (for example silver-platinum, calomel-platinum) but tests have s

26、hown that better potential increments are obtained with the electrode pairs indicated above. NOTEA manual procedure has been described, but automatic devices can obviously be used. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of e

27、quivalent purity. 4.1 Acetone 4.2 Nitric acid, approximately1,40g/ml, about68 % (m/m) solution. 4.3 Potassium nitrate, solution saturated at room temperature. 4.4 Silver nitrate, solution, c(AgNO 3 ) = 0,1mol/l approximately. Dissolve8,5g of silver nitrate in a500ml one-mark volumetric flask, dilute

28、 to the mark and mix. Store the solution in a dark glass bottle. 4.5 Silver nitrate, solution, c(AgNO 3 ) = 0,01or0,004mol/l approximately. Select the appropriate solution according to the information in the Table relating to6.1. Prepare the selected solution at the time of use from the silver nitra

29、te solution (4.4), diluting when required in a one-mark volumetric flask. NOTEIf solution4.4 is used directly, as indicated in the Table relating to6.1, it should be standardized according to the procedure specified in6.2. If the solutions prepared from that specified in4.4 are used (see4.5), the ca

30、libration of solution4.4 is not necessary. It is sufficient to standardize the solution selected in4.5, in all cases according to the procedure specified in6.2. 4.6 Potassium chloride, standard reference solution, c(KCl) = 0,1mol/l exactly. Weigh, to the nearest0,0001g, 3,7276g of potassium chloride

31、, previously dried for1h at about130 C and cooled in a desiccator. Dissolve in a little water and transfer the solution quantitatively into a 500ml one-mark volumetric flask. Dilute to the mark and mix. This solution shall not be kept for more than one month. 4.7 Potassium chloride, standard referen

32、ce solution c(KCl) = 0,01or0,004mol/l exactly. Use the solution of concentration corresponding to that of the silver nitrate solution selected for the titration. Prepare this solution at the time of use from thestandard reference potassium chloride solution(4.6), diluting when required in a one-mark

33、 volumetric flask. 5 Apparatus Ordinary laboratory apparatus and 5.1 Potentiometric titration apparatus, comprising: 5.1.1 Potentiometer, sensitivity at least2mV, covering the range 500to+500mV. 5.1.2 Reference electrodes 5.1.2.1 Calomel electrode, fitted with a reservoir filled with saturated potas

34、sium chloride solution, orBS6337-4:1984 2 BSI 10-1999 5.1.2.2 Mercury(I) sulphate electrode 5.1.3 Bridge, containing some of the saturated potassium nitrate solution (4.3), connected to the calomel electrode (5.1.2.1) and fitted with porous diaphragms at the ends, to be used only if a calomel electr

35、ode is used. 5.1.4 Measuring electrodes 5.1.4.1 Silver electrode, or 5.1.4.2 Chloride or silver ion-selective electrode 5.2 Magnetic stirrer, with a polytetrafluorethylene (PTFE)-coated rod. 5.3 Burettes with a fine-pointed tip, graduated in0,02or0,01ml divisions. 6 Procedure 6.1 Test portion and pr

36、eparation of the test solution Weigh a mass of the test sample and prepare the test solution following the procedure specified in the International Standard relating to the product to which the method is to be applied, taking care that the chloride ion concentration in the test solution, expressed i

37、n milligrams per litre, is between1and1500. According to the expected chloride ion content, use either all the test solution or a suitable aliquot portion and, for the titration, a silver nitrate solution of appropriate concentration as indicated, for example only, in the Table below. 6.2 Determinat

38、ion of the blank test and standardization of the selected silver nitrate solution 6.2.1 Preparation of the blank test solution At the same time as the determination (6.3), carry out a blank test using the same quantities of all the reagents used for the preparation of the test solution but omitting

39、the test portion. Adjust the volume of the solution to the same as that of the test solution. NOTEIf all the test solution is taken for the determination, prepare the blank test solution in duplicate in order to carry out the two titrations envisaged in6.2.2 and6.2.3. 6.2.2 Preparation of the soluti

40、on to be standardized Place the blank test solution (6.2.1) or an aliquot portion of volume equal to that used for the determination (see the Table relating to6.1) in a beaker of suitable capacity. Add, using one of the burettes (5.3),5,00ml of the appropriate standard reference potassium chloride s

41、olution (4.6 or4.7). If the resulting solution is alkaline, neutralize it using the nitric acid solution (4.2), cooling if necessary, and then add an excess of2ml of this acid. Add to the beaker such a quantity of the acetone(4.1) as will give a ratio of acetone to aqueous solution preferably equal

42、to80/10(V/V) but, in any case, not lower than50/50(V/V). However, if the concentration of the silver nitratesolution to be used is greater than c(AgNO 3 )= 0,01mol/l, the acetone can be omitted. NOTEThe solution to be titrated should have a volume of at least 50ml to avoid attack of the silver elect

43、rode by the nitric acid solution. 6.2.3 Titration Introduce into the beaker a magnetic stirrer rod(5.2), place the beaker on the stirrer and set it in motion. Introduce in the solution the measuring electrode (5.1.4) and the reference electrode (5.1.2). If, however, a calomel electrode (5.1.2.1) is

44、to be used, introduce one end of the bridge (5.1.3) instead of the reference electrode and immerse the other end in a beaker of water containing the calomel electrode. Connect the electrodes to the potentiometer (5.1.1) and note the initial value of the potential, after having checked the zero setti

45、ng of the instrument. Titrate, using a second burette (5.3), adding the silver nitrate solution corresponding to the same concentration of the standard reference potassium chloride solution used in0,1ml increments for the 0,004mol/l solution and in0,05ml increments for0,01and0,1mol/l solutions. Afte

46、r each addition, wait for the potential to reach a steady value. Note, in the first two columns of a Table, the successive volumes added and the corresponding potentials. In a third column, note the successive increments (% 1 E) of the potential E. In a fourth column, note the differences (% 2 E), p

47、ositive or negative, between the potential increments (% 1 E). The end of the titration corresponds to the addition of the0,2ml, 0,1ml or0,05ml (V 1 ) of the silver nitrate solution, which gives the maximum value of% 1 EBS6337-4:1984 BSI 10-1999 3 Table The exact volume (V EQ ) of the silver nitrate

48、 solution corresponding to the end of the reaction is given by the formula where Repeat the operations specified in 6.2.2 and 6.2.3, this time using10,00ml instead of5,00ml, of the standard reference potassium chloride solution. NOTEIf the expected titration is known approximately, most of the titra

49、nt can be added as one increment. Thus, in the particular case, for the5,00ml of the standard reference potassium chloride solution, 4ml and for the10,00ml, 9ml of the titrant can be added immediately. 6.2.4 Calculation of concentration of the solution The concentration of the silver nitrate solution, expressed as moles of AgNO 3per litre, is given by the formula where 6.2.5 Calculation of value of blank test The value of the reagent blank test, V 4 , is given, in millilitres, by the formula V 4= 2 V 3 V 2 where V 2and V 3are as defined in6.2.4. 6.3 Determ