1、BSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06Leather - Chemical determination of chromic oxide contentPart 1: Quantification by titrationBS EN ISO 53981:2018National forewordThis British Standard is the UK implementation of EN ISO 53981:2018. It is identical to IS
2、O 53981:2018. It supersedes BS EN ISO 53981:2007, which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee TCI/69, Footwear Clause 5 refers to ISO 4044 for preparing the sample rather than grinding the leather.A list of all parts in the ISO 5398 series can be f
3、ound on the ISO website.iv ISO 2018 All rights reservedBS EN ISO 53981:2018ISO 5398-1:2018IntroductionThe ISO 5398 series consists of four parts, each describing methods suitable for the determination of the chromic oxide content in leather. The different techniques have been described to reflect th
4、e variations in industrial practice compared with the more sensitive analytical equipment available for test laboratories. Variations also exist in the range of chromic oxide that the methods are deemed suitable to quantify.This document describes a traditional technique applied in industry that doe
5、s not require the use of advanced analytical equipment. ISO 2018 All rights reserved vBS EN ISO 53981:2018This page deliberately left blankLeather - Chemical determination of chromic oxide content Part 1: Quantification by titration1 ScopeThis document describes a method for the determination of chr
6、omium in aqueous solution obtained from leather. This is an analysis for total chromium in leather; it is not compound specific or specific to its oxidation state.This method describes the determination of chrome by iodometric titration and is to be applicable to chromiumtanned leathers which are ex
7、pected to have chromic oxide contents in excess of 0,3 %. Two different methods are described as alternatives for obtaining chromium in a suitable solution. It is appropriate to use either method.2 Normative referencesThe following documents are referred to in the text in such a way that some or all
8、 of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 2418, Leather Chemical, physical and mechanical and fastness tests Sampling
9、locationISO 3696, Water for analytical laboratory use Specification and test methodsISO 4044, Leather Chemical tests Preparation of chemical test samplesISO 4047, Leather Determination of sulphated total ash and sulphated water-insoluble ashISO 4684, Leather Chemical tests Determination of volatile
10、matter3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.ISO and IEC maintain terminological databases for use in standardization at the following addresses: ISO Online browsing platform: available at https:/www.iso.org/obp IEC Electropedia: available
11、 at http:/www.electropedia.org/3.1chromic oxide contentamount of chromium in leather, determined by this method and reported as chromic oxideNote 1 to entry: The chromic oxide content is expressed in per cent by mass, based on dry matter.4 PrincipleThe chromium present in the leather is solubilized
12、in the hexavalent state followed by analysis of the solution by iodometric titration.INTERNATIONAL STANDARDISO 5398-1:2018(E) ISO 2018 All rights reserved 1BS EN ISO 53981:2018ISO 5398-1:20185 Sampling and sample preparationSample in accordance with ISO 2418, and prepare the leather in accordance wi
13、th ISO 4044. If sampling in accordance with ISO 2418 is not possible (as in the case of leathers from finished products like shoes or garments), details about sampling shall be given together with the test report.Weigh accurately the prepared leather to the nearest 0,001 g. (Suggested masses are ful
14、l chrome leather 1 g, semichrome leather 2 g, leather with low chrome content 2 g to 5 g.) From every leather sample, a minimum of two determinations shall be made.6 ReagentsUnless otherwise stated, only analytical grade chemicals are to be used. The water shall be grade 3 in accordance with ISO 369
15、6. All solutions are aqueous solutions.6.1 Wet oxidation method6.1.1 Nitric acid, 70 %.6.1.2 Sulfuric acid, concentrated (98 %), and perchloric acid (60 % to 70 %), mixed together in the ratio of 1:3 by volume.6.1.3 Orthophosphoric acid, 90 %.6.2 Alkaline fusion method6.2.1 Fusion mixture, consistin
16、g of equal masses of sodium carbonate (Na2CO3), potassium carbonate (K2CO3) and sodium tetraborate (Na2B4O7).6.2.2 Hydrochloric acid, concentrated (37 %).6.3 Iodometric titration6.3.1 Potassium iodide solution, freshly prepared, 100 g/l.6.3.2 Sodium thiosulfate, 0,1 mol/l standardized solution in wa
17、ter.6.3.3 Starch indicator solution, 10 g/l (or soluble starch powder).7 ApparatusThe usual laboratory apparatus is required and, in particular, the following.7.1 Conical flask, 500 ml, with ground glass stopper.7.2 Crucible, glazed porcelain or platinum (required for alkaline fusion method only).7.
18、3 Burette, 50 ml.7.4 Filtration device, using simple paper, glass fibre (GFC) or membrane type filters.7.5 Antibumping granules (or similar) (wet oxidation method).2 ISO 2018 All rights reservedBS EN ISO 53981:2018ISO 5398-1:20188 Methods8.1 Preparation of analytical solution8.1.1 Wet oxidation meth
19、odWARNING It is imperative that nitric acid is added first because of the possible explosive reaction of perchloric acid with leather.Accurately weigh a mass of leather (see Clause 5) into the conical flask (7.1). Add 10 ml of nitric acid (6.1.1) and allow to stand for 2 min. Add 15 ml of mixed sulf
20、uric/perchloric acids (6.1.2) and a few antibumping granules (7.5). Place a funnel or splash bulb in the neck of the flask and heat to boiling on a wire gauze over a moderate flame. As soon as the reaction mixture begins to turn orange, lower the flame. After a complete change of colour, heat gently
21、 for at least 2 min. Allow to cool in air for 5 min and dilute to approximately 200 ml. Boil for 10 min to eliminate any chlorine. Allow to cool and add 5 ml of orthophosphoric acid (6.1.3) to mask any iron.The use of a sulfuric/perchloric acid mixture is preferred to the use of the individual acids
22、 as it prevents the accidental use of perchloric acid alone.In the case of incomplete oxidation (i.e. the solution does not change to an orange colour), it is permissible to add further mixed sulfuric/perchloric acid to the sample.8.1.2 Alkaline fusion methodAsh the accurately weighed sample of leat
23、her (see Clause 5) in accordance with ISO 4047. In the crucible (7.2) containing the leather ash, carefully add 5 g of fusion mixture (6.2.1) and mix well using a platinum wire or thin glass rod. Start by heating the crucible gently on an open flame, then heat more fiercely for approximately 30 min.
24、 (A muffle furnace operating at 750 C 50 C for at least 30 min may be used to heat the melt.) After cooling, place the crucible in a beaker containing 100 ml to 150 ml of boiling water and continue to heat the water until the fusion mixture has completely dissolved. Filter (7.4) the solution obtaine
25、d into the conical flask (7.1). Thoroughly wash the beaker, crucible and filter with hot water, collecting the washings in the flask. Carefully add at least 10 ml hydrochloric acid to the flask and allow to cool down to room temperature.8.2 Measurement of the aqueous solutionAdd to the solution obta
26、ined from 8.1.1 or 8.1.2 20 ml of potassium iodide solution (6.3.1), stopper the flask and leave to stand for 10 min in the dark. Titrate with 0,1 mol/l sodium thiosulfate solution (6.3.2) until the solution in the flask is either light green or blue using 5 ml of starch indicator solution (6.3.3) (
27、or a small quantity of starch powder), added towards the end of titration. Note the millilitres of thiosulfate solution used.If starch solution is used, it should either be freshly prepared or should have been prepared with the addition of a little mercuric iodide to preserve the solution for severa
28、l months.If the titre is in excess of 50 ml, the analysis should be repeated using either smaller sample size or with appropriate dilution of the solution obtained from 8.1.1 or 8.1.2.9 Calculation and expression of results9.1 GeneralCalculate the following percentage. ISO 2018 All rights reserved 3
29、BS EN ISO 53981:2018ISO 5398-1:2018The percentage by mass on dry matter, wCr, of chromic oxide, Cr2O3, in the leather is given by the equationwVFmCr100,00253 100=whereV1is the volume, in millilitres (ml), of 0,1 mol/l thiosulfate solution used for the titration;m0is the mass of the original leather
30、sample, in grams (g);F is the factor to correct to 0 % volatile matter; it is calculated as follows:Fw=100100Wwhere wWis the volatile matter content, according to ISO 4684 (see Annex A), in per cent by mass.NOTE 1 ml of exactly 0,1 mol/l thiosulfate solution is equivalent to 0,002 53 g Cr2O3.It is a
31、lso permissible, if required, to quote the results based on the dry, degreased mass of the sample.9.2 RepeatabilityThe results of the duplicate determination should not differ by more than 0,1 % calculated on the original mass of the leather.10 Test reportThe test report shall include the following:
32、a) a reference to this document, i.e. ISO 53981;b) a description of the leather;c) a reference to the method used for sample preparation, type of digestion and measurement;d) the volatile matter content of the leather, in per cent;e) the results obtained based on dry sample mass to one decimal place
33、, in per cent;f) details of any deviations from the described procedures.4 ISO 2018 All rights reservedBS EN ISO 53981:2018ISO 5398-1:2018Annex A (informative) Determination of water and other volatile matterThe volatile matter content of leathers is determined according to ISO 4684. The volatile ma
34、tter content of the leather is determined from a sample of ground leather prepared for the chromium determination. Wet leathers are dried before the determination of the volatile matter content according to ISO 4684. The loss in mass during initial drying is added to the loss in mass after drying ac
35、cording to ISO 4684. ISO 2018 All rights reserved 5BS EN ISO 53981:2018This page deliberately left blankBSI is the national body responsible for preparing British Standards and other standards-related publications, information and services.BSI is incorporated by Royal Charter. British Standards and
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