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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 22807-2008 Leather and fur - Chemical tests - Determination of chromium VI content.
The following main technical changes have been made with respect to GB/T 22807-2008:
——normative references of GB/T 6682 and GB/T 38402 are added (see Clause 2 of this standard, and Clause 2 of Edition 2008);
——the specific test conditions involved in the principle are deleted and some contents are adjusted to "7.1 Preparation of analytical solution" (see Clause 3 and 7.1 of this standard, and Clause 3 of Edition 2008);
——methanol is added to the “Reagents and materials” (see 4.9 of this standard);
——the frequency requirement of the oscillator is modified (see 5.1 of this standard, and 5.1 of Edition 2008);
——the filter paper and analytical balance are added to the “Apparatus” (see 5.7 and 5.11 of this standard);
——the temperature, temperature control mode and mechanical oscillation frequency of specimen extraction are specified (see 7.1 of this standard);
——the allowable range of pH value of the extracted solution is relaxed; the filtration method of the extract is adjusted to filter paper filtration (see 7.1 of this standard, 7.3 of the Edition 2008);
——the decolorization operation procedure of specimen extract is added (see 7.2.1 of this standard);
——the dispute settlement methods are added (see 8.4 of this standard).
This standard is modified in relation to ISO 17075-1:2007, Leather - Chemical determination of chromium (VI) content in leather - Part 1: Colorimetric method.
This standard is changed largely from ISO 17075-1:2017 in terms of structure. See Annex A for cross references to the clauses/ subclauses between this standard and ISO 17075-1:2017.
Technical differences have been made in this standard with respect to ISO 17075-1:2017, and relevant technical differences and their causes have been listed in Annex B.
The following editorial changes have also been made in this standard:
——the standard name is changed to Leather and fur - Chemical tests - Determination of chromium (VI) content: Colorimetric method;
——in 4.3, a description is added to the situation that the discolored 1,5-diphenylcarbazide (DPC) solution cannot be used;
——the informative annexes "Annex A" and "Annex B" in ISO 17075-1:2017 are deleted;
——the validation data in Annex C of ISO 17075-1:2017 is adjusted to the results of validation in national laboratories.
This standard was proposed by China National Light Industry Council.
This Standard is under the jurisdiction of the National Technical Committee 252 on Leather of Standardization Administration of China (SAC/TC 252).
The previous edition of this standard is as follows:
——GB/T 22807-2008.
Leather and fur - Chemical tests - Determination of chromium (VI) content: Colorimetric method
1 Scope
This standard specifies a colorimetric method for the determination of chromium (VI) content in leather and fur.
The method described is applicable to quantify the chromium (VI) content in various leathers, furs and their products.
2 Normative references
The following referenced documents are indispensable for the application 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.
GB/T 6682 Water for analytical laboratory use - Specification and test methods (GB/T 6682-2008, ISO 3696:1987, MOD)
GB/T 38402 Leather and fur - Chemical tests- Determination of chromium (VI) content: Chromatographic method (GB/T 38402-2019, ISO 17075-2: 2017, MOD)
QB/T 1267 Fur - Chemical, physical and mechanical and fastness tests - Sampling location (QB/T 1267-2012, ISO 2418: 2002, MOD)
QB/T 1272 Fur - Preparation of chemical test samples (QB/T 1272-2012, ISO 4044: 2008, MOD)
QB/T 1273 Fur - Chemical tests - Determination of volatile matter (QB/T 1273-2012, ISO 4684:2005, MOD)
GB/T 2706 Leather - Chemical, physical and mechanical and fastness tests - Sampling location (QB/T 2706-2005, ISO 2418:2002, MOD)
GB/T 2716 Leather - Preparation of chemical test samples (QB/T 2716-2018, ISO 4044:2008, MOD)
QB/T 2717 Leather - Chemical tests - Determination of volatile matter (QB/T 2717-2018, ISO 4684:2005, MOD)
3 Principle
Extractable chromium (VI) is leached from the specimen in phosphate buffer and coextracted coloured substances which influence the detection are removed by solid phase extraction if necessary. After filtration, chromium (VI) in the filtrate is reacted with 1,5-diphenylcarbazide under acidic conditions to generate a red/violet complex. Measure the absorbance of the complex at a specified wavelength, and calculate the content of chromium (VI).
4 Reagents and materials
Unless otherwise specified, analytical reagents shall be adopted.
4.1 Water, which shall meet the requirements for Grade 3 water specified in GB.T 6682.
4.2 Phosphate buffer (0.1 mol/L): Dissolve 22.8 g dipotassium hydrogenphosphate (K2HPO4?3H2O, with the relative molecular mass of 228) in 1,000 mL distilled water, adjusted to pH 8.0 ± 0.1 with phosphoric acid (4.4). Degas this solution with either argon or nitrogen (4.8) or ultrasonic bath.
Note: Phosphate buffer is recommended to be freshly prepared. However, the solution may be kept for up to one week at 0℃ to 4℃ but shall be warmed to room temperature and degassed prior to use.
4.3 1,5-Diphenylcarbazide (DPC) solution: Dissolve 1.0 g 1,5-diphenylcarbazide in 100 mL acetone, and acidified with one drop of glacial acetic acid.
Note: The solution shall be kept in a brown glass bottle and stored under protection from light at 0℃ to 4℃, with the shelf life up to 14 days. The solution can no longer be used if it has obvious discoloration (especially pink).
4.4 Phosphoric acid (H3PO4) solution: Dilute 700 mL phosphoric acid (with a mass fraction of 85% and a density of 1.71 g/mL) to 1,000 mL with distilled water.
4.5 Potassium dichromate (K2Cr2O7) reference substance: dried for (16 ± 2) h at (102 ± 2)℃ before use.
4.6 Chromium(VI) standard stock solution (1 mg/mL): Weigh 2.829 g potassium dichromate (4.5), dissolve with distilled water, transfer, rinse, and dilute it to the scale into a 1,000-mL volumetric flask. One mL of this solution contains 1 mL of chromium.
4.7 Chromium (VI) standard solution (1 μg/mL): Pipette 1 mL chromium (VI) standard stock solution (4.6) into a 1,000-mL volumetric flask and dilute it to the scale with phosphate buffer (4.2). One mL of this solution contains 1 μg of chromium.
Note 1: The solution may be kept for up to one week at 0 ℃ to 4 ℃ but shall be warmed to room temperature prior to use.
Note 2: The chromium (VI) standard solution (1 μg/mL) may be directly prepared by using the commercially available standard solution at present. The standard samples of chromium (VI) on the market include "Standard Solution of Cr (VI)".
4.8 Argon (or nitrogen, argon is recommended): oxygen-free, purity ≥ 99.99%.
Note: The relative density of argon is higher than that of air, and it is not easy to escape upward when opened.
4.9 Methanol, chromatographically pure.
5 Apparatus
5.1 Mechanical oscillator, horizontal oscillation, with a frequency of (100 ± 10) times/min.
5.2 Conical flask, of capacity 250 mL, with ground stopper.
5.3 Aeration tube and flow meter, suitable for a flow rate of (50 ± 10) mL/min.
5.4 pH meter with glass electrode, to the nearest of 0.1.
5.5 Volumetric flasks, of capacities 25 mL, 100 mL and 1,000 mL.
5.6 Pipettes, of nominal capacity.
5.7 Filter paper.
5.8 Spectrophotometer, with the wavelength of 540 nm.
5.9 Quartz cuvette, 2 cm thick, or other cuvette with suitable thickness.
5.10 Solid phase extraction column, C18 or PA, or filler with equivalent effect.
5.11 Analytical balance: with precision of 0.1 mg.
Foreword i
1 Scope
2 Normative references
3 Principle
4 Reagents and materials
5 Apparatus
6 Sampling and preparation of specimens
7 Test procedures
8 Calculation and expression of results
9 Test report
Annex A (Informative) Structural changes of this standard with respect to ISO 17075-1:
Annex B (Informative) Technical differences and their causes between this standard and ISO 17075-1:
Annex C (Informative) Comparison between colorimetric method (GB/T 22807) and chromatographic method (GB/T 38402)
