1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION METAYHAPOAHAII OPAHW3AUHJl IlO CTAHAAF-TM3AUHH.ORGANl.SATlON INTERNATIONALE DE NORMALISATION General method for the determination of arsenic - Silver diethyldithiocarbamate photometric method First edition - 1973-05-01 UDC 546.19
2、: 543.42 Ref. No. IS0 2590-1973 (E) Descriptors : chemical analysis, determination of content, arsenic, photometry. Price based on 5 pages Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without lice
3、nse from IHS-,-,-FOREWORD IS0 (the International Organization for Standardization) is a worldwide federation of national standards institutes (IS0 Member Bodies). The work of developing international Standards is carried out through IS0 Technical Committees. Every Member Body interested in a subject
4、 for which a Technical Committee has been set up has the right to be represented on that Committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the Technical Committees are circulated to the
5、 Member Bodies for approval before their acceptance as International Standards by the IS0 Council. International Standard IS0 2590 was drawn up by Technical Committee lSO/TC 47, Chemistry, and circulated to the Member Bodies in November 1971. It has been approved by the Member Bodies of the followin
6、g countries : Austria Netherlands Belgium New Zealand Egypt, Arab Rep. of Poland France Portugal Hungary Romania India South Africa, Rep. of Israel Spain Italy Sweden Switzerland Thailand Turkey United Kingdom U.S.A. U.S.S.R. The Member Body of the following country expressed disapproval of the docu
7、ment on technical grounds : Germany 0 International Organization for Standardization, 1973 l Printed in Switzerland Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-INTERN
8、ATIONAL STANDARD IS0 2590 -1973 (E) General method for the determination of arsenic - Silver diethyldithiocarbamate photometric method 1 SCOPE This International Standard specifies a general method for the photometric determination of arsenic, using silver diethyldithiocarbamate. Store the solution
9、in a tightly sealed, dark glass bottle, protected from light. This solution remains stable for about 2 weeks. 4.3 Arsenic standard solution, 0,100 g/l. 2 FIELD OF APPLICATION The method is applicable to the determination of quantities of arsenic (As), contained either in all the test solution or in
10、the aliquot portion taken for the determination, of between 1 and 20 pg. 3 PRINCIPLE Reduction of the arsenic by zinc in a hydrochloric acid medium, with the formation of arsine. Weigh, to the nearest 0,000 1 g, 0,132 0 g of arsenic trioxide (As*Oa) and transfer it to a beaker of suitable capacity (
11、for example, 100 ml). Dissolve the arsenic trioxide in about 2 ml of 50 g/l sodium hydroxide solution. Transfer the solution quantitatively to a 1 000 ml one-mark volumetric flask. Wash the beaker several times, collecting the wash water in the volumetric flask, dilute to the mark and mix. 1 ml of t
12、his standard solution contains 100 /-rg of As. 4.4 Arsenic standard solution, 2,50 mg/l. Absorption of the arsine in a solution of silver diethyldithiocarbamate in pyridine. Transfer 25.0 ml of the arsenic standard solution (4.3) to a 1 000 ml one-mark volumetric flask, dilute to the mark and Photom
13、etric measurement of the purplish-red colour produced by the colloidally dispersed silver at the maximum of the absorption curve (wavelength approximately 540 nm). mix. Prepare this solution immediately before use. 1 ml of this standard solution contains 2.5 pg of AS. 4.5 Absorbent cotton wool satur
14、ated with lead acetate. NOTE - The reaction of the formation of the colloidal silver is : AsH3 + 6 Ag(DDTC) = 6 Ag + 3 H(DDTC) + As(DDTCj3 4 REAGENTS Dissolve 50 g of lead acetate trihydrate Pb(C2H302)2.3H20 in 250 ml of water. Saturate the absorbent cotton wool with this solution, remove the excess
15、 solution by allowing it to drain and dry the cotton wool under vacuum at room temperature. All the reagents, and the zinc in particular, shall be free from arsenic or have a very low arsenic content. Store it in an air-tight container. 4.6 Potassium iodide, 150 g/l solution. Distilled water, or wat
16、er of equivalent purity, shall be used in the test. Dissolve 15 g of potassium iodide in water, dilute to 100 ml and mix. 4.1 Hydrochloric acid, p approximately I,19 g/ml, 4.7 Tin(ll) chloride, hydrochloric acid solution. about 38 % (m/m) solution, or approximately 12 N. Dissolve 40 g of tin(ll) chl
17、oride dihydrate (SnC12.2H20) in 4.2 Silver diethyldithiocarbamate, Ag(DDTC), 5 g/l a mixture of 25 ml of water and 75 ml of the hydrochloric solution in pyridine. acid solution (4.1). Dissolve 1 g of silver diethyldithiocarbamate in pyridine 4.8 Zinc shot, 0,5 to 1 mm, or any other form of zinc (p a
18、pproximately 0,980 g/ml) and dilute to 200 ml with the which has been shown, by experiment, to give equivalent same pyridine. results under the specified test conditions (see Annex). 1 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo rep
19、roduction or networking permitted without license from IHS-,-,-IS0 2590-1973 (E) 5 APPARATUS All the glass containers used for the determination of arsenic shall be washed with hot concentrated sulphuric acid, taking the necessary precautions, rinsed thoroughly with water and dried completely. Ordin
20、ary laboratory apparatus and 6.3 Preparation of the calibration curve 5.1 Glass apparatus with ground glass joints, for the liberation and total absorption of the arsine. NOTE - See lSO/R 383 and ISO/R 541 for details of conical and spherical ground glass joints. A suitable apparatus is shown in the
21、 Figure, and consists of : 5.1.1 Conical flask, 100 ml capacity, for the liberation of the arsine. 5.1.2 Connecting tube, to trap hydrogen sulphide. 5.1.3 15-Bulb absorption vessel. 5.2 Spectrophotometer, or 5.3 Photoelectric absorptiometer, fitted with filters giving a maximum transmission between
22、520 and 560 nm. 6 PROCEDURE WARNING - Because of the toxicity and unpleasant odour of pyridine, it is recommended that it should be handled with care and in a well-ventilated fume cupboard. 6.1 Test portion and preparation of the test solution Weigh the quantity of the test sample indicated in the I
23、nternational Standard relating to the product concerned and treat it in the appropriate manner so as to obtain a test solution according to the conditions described below. In general, the test solution should be prepared so that its total volume, or that of the aliquot portion taken for the determin
24、ation, is 40 ml, and so that it contains between 1 and 20 pg of As and 10 ml of the hydrochloric acid solution (4.1). The resulting acidity is about 3 N before the addition of the potassium iodide solution. The test solution must be absolutely free from nitrate ions; moreover, certain elements (coba
25、lt, mercury, silver, copper, molybdenum, palladium, etc.) will reduce ,the yield of arsine. The procedure should, if necessary, indicate how to take account of their presence. NOTE - In the case where the test solution is necessarily a sulphuric acid medium, the acidity of the 40 ml of test solution
26、 should be about 3.8 to 4 N (containing 10 ml of an approximately 15 N sulphuric acid solution). 6.2 Blank test Detach the absorption vessel (5.1.3). swirl in order to dissolve the red deposit formed in the lower part and completely mix the solution. Carry out a blank test in parallel with the deter
27、mination, The colour of the solution is stable, in the absence of light, following the same procedure and using the same quantities for about 2 h and the measurements shall be carried out of all the reagents used for the determination. within this period. The calibration curve shall be prepared each
28、 time that a new batch of zinc is used and each time that a new solution of silver diethyldithiocarbamate is prepared. 6.3.1 Preparation of the standard matching solutions for photometric measurements with a 1 cm cell. Transfer into six separate conical flasks (5.1.1) the volumes of the arsenic stan
29、dard solution (4.4) indicated in the following table : Volume of the arsenic standard solution (4.4) ml 1 Corresponding mass of arsenic PS OX 0 1 ,oo 2.5 333 5 4.00 10 6.00 15 8.00 20 * Compensation solution Add to each flask 10 ml of the hydrochloric acid solution (4.1) and the quantity of water ne
30、cessary to make up to about 40 ml. Add 2 ml of the potassium iodide solution (4.6) and 2 ml of the tin(ll) chloride solution (4.7); swirl and then allow to stand for 15 min. NOTE - In the case of test solutions in a sulphuric acid medium, instead of adding 10 ml of the hydrochloric acid solution, ad
31、d 10 ml of an approximately 15 N solution of sulphuric acid. Place a little of the absorbent cotton wool (4.5) in the connecting tube (5.1.2) in order to absorb any hydrogen sulphide which may be released with the arsine. Grease the ground glass joints with a grease that is insoluble in pyridine, tr
32、ansfer 5,0 ml of the silver diethyl- dithiocarbamate solution (4.2) to the absorption vessel (5.1.3) and attach the connecting tube (5.1.2) to the absorption vessel by means of a safety clip. After allowing to stand for 15 min. add to the conical flask (5.1.1), with the aid of a powder funnel, 59 of
33、 the zinc (4.6) and rapidly assemble the apparatus as indicated in the Figure. Allow approximately 45 min for the reaction to take place. 2 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without lic
34、ense from IHS-,-,-1so2590-1973(E) 6.3.2 Photometric measurements Carry out the measurements using the spectrophotometer (5.2) at the maximum of the absorption curve (wavelength approximately 540 nm), or with the photoelectric absorptiometer (5.3), fitted with suitable filters, after having adjusted
35、the instrument, in each case, to zero absorbance against the compensation solution. 6.3.3 Preparation of the calibration chart Plot a graph having, for example, the arsenic contents in micrograms per 5 ml of standard matching solution as abscissae, and the corresponding values of absorbance as ordin
36、ates. 6.4 Determination To 40 ml of the test solution (6.1). contained in the conical flask (5.1.1), add 2 ml of the potassium iodide solution (4.6) and 2 ml of the tin(ll) chloride solution (4.7); swirl, and allow to stand for 15 min. Complete the operations according to the procedure described in
37、6.3.1. 6.4.1 Photometric measurement Carry out the photometric measurement on the test solution according to the method described in 6.3.2, after having adjusted the instrument to zero absorbance against the blank test solution (6.2). 7 EXPRESSION OF RESULTS By means of the calibration chart (see 6.
38、3.3), determine the quantity of arsenic (As) corresponding to the value of the photometric measurement on the test solution. The International Standards relating to the product in question will give the formulae to be applied for the final calculation. 3 Copyright International Organization for Stan
39、dardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,- 15 bulbs, total height = 250 Total volume of the 15 bulbs = 14 ml Copyright International Organization for Standardization Provided by IHS under license with ISONot f
40、or ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 2590-1973 (E) ANNEX USE OF ZINC IN NEEDLE FORM When, for any reason, zinc in the form of needles is used in place of zinc shot, the following modifications shall be made to the method : 6.3.1 2nd paragraph - read : “Ad
41、d to each flask 10 ml of the hydrochloric acid solution (4.1) and the quantity of water necessary to make up the volume to about 30 ml. Add 2 ml of the potassium iodide solution (4.6) and 2 ml 4.8 read : “Zinc, in needles 2 to 3 mm in diameter.” of the tin( I I) chloride solution (4.7); . I 6.1 2nd
42、paragraph - read : “In general, the test solution should be prepared so that its total volume, or that of the aliquot portion taken for the determination, is 30 ml, and so that it contains 1 to 2Oug of As and 10 ml of the hydrochloric acid solution (4.1). The acidity is about 4 N before the addition of the potassium iodide solution” Penultimate paragraph - read : “Allow 1 h for the reaction to take place.” 5 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
