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GB/T 19941 Leather and fur - Determination of formaldehyde content consists of the following three parts:
——Part 1: High performance liquid chromatography method;
——Part 2: Colorimetric method;
——Part 3: Formaldehyde emissions.
This is part 2 of GB/T 19941.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces the colorimetric method specified in GB/T 19941-2005 Leather and fur - Chemical tests - Determination of formaldehyde content.
The following main technical changes have been made with respect to GB/T 19941-2005:
——normative references of QB/T 1273, QB/T 2717, and GB/T 19941.1 are added, and normative references of QB/T 1266 and QB/T 2707 are deleted (see clause 2 of this standard; and clause 2 of Edition 2005);
——clause 3 "Principle" is modified (see clause 3 of this standard; and 5.1 of Edition 2005);
——"sodium dodecylsulfate" is added as extraction solution (see 4.2 of this standard);
——the validity period of Nessler’s reagent is modified (see 4.3 of this standard; and 5.2.2 of Edition 2005);
——the requirements are deleted for air conditioning before weighing in specimen preparation (see 5.4.2.3 of Edition 2005);
——the types and specifications of glassware in instruments and apparatus are modified (see clause 5 of this standard; and 5.3 of Edition 2005);
——the composition of blank solution in "Testing other compounds which cause a coloring with acetylacetone" is modified, and the treatment method when absorbance is greater than 0.05 is added (see 6.5 of this standard; and 5.4.6 of Edition 2005);
——the provision is added that the formaldehyde standard solution may be directly prepared with commercial standard materials (see 6.6);
——the calculation formula for formaldehyde content is modified (see 6.7 of this standard; and 5.4.8 of Edition 2005);
——relevant provisions for test results calculated on the basis of dry substance, detection limit of methods and method for dispute settlement are added (see clause 7 of this standard);
——the requirements are deleted for "description and packaging method of test samples", "analytical method used" and "test personnel and date" in clause 8 “Test report" (see clause 7 of Edition 2005);
——the preparation of formaldehyde stock solution, determination of formaldehyde concentration and related reagents and apparatus are transferred to Annex C, the titration times of blank solution in formaldehyde stock solution is added, and the molecular mass of formaldehyde is modified to 30.02 g/mol (see Annex C of this standard; and clause 3 of Edition 2005).
This part has been redrafted and modified in relation to ISO 17226-2: 2018 Leather - Chemical determination of formaldehyde content - Part 2: Method using colorimetric analysis.
This part has been changed largely from ISO 17226-2: 2018 in terms of structure. See Annex A for the comparison between this part and ISO 17226-2: 2018 in clause NO.
Technical differences have been made in this part with respect to ISO 17226-2: 2018, and relevant technical differences and their causes have been listed in Annex B.
The following editorial changes have been made in this part:
——the standard name is changed to Leather and fur - Determination of formaldehyde content - Part 2: Colorimetric method;
——notes to the measured formaldehyde are added in clause 3 “Principle";
——the example of diluted filtrate in "8.2.3 Reaction with acetylacetone” of ISO 17226-2: 2018 is deleted;
——Annex A to ISO 17226-2:2018 is deleted.
This part was proposed by the China National Light Industry Council.
This part is under the jurisdiction of National Technical Committee 252 on Leather of Standardization Administration of China.
The previous edition replaced by this part is as follows:
——GB/T 19941-2005.
Leather and fur - Determination of formaldehyde content - Part 2: Colorimetric method
1 Scope
This part of GB/T 19941 specifies a colorimetric method for the determination of free and hydrolyzed formaldehyde content in leathers and furs.
This standard is applicable to the determination of formaldehyde contents 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 19941.1 Leather and fur - Determination of formaldehyde content - Part 1: High performance liquid chromatography method (GB/T 19941.2-2019, ISO 17226-1: 2018, 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)
QB/T 2706 Leather - Chemical, physical and mechanical and fastness tests - Sampling location (QB/T 2706-2005, ISO 2418: 2002, MOD)
QB/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
The specimen is extracted with an extraction solution under specified conditions, and the obtained extraction solution is mixed with acetylacetone, whereby formaldehyde reacts to give a yellow compound (3,5-diacetyl-1,4-dihydrolutidine). The absorbance of this compound is measured at the specified wavelength, and the formaldehyde content in the specimen is calculated.
Note 1: The determination result of this method is taken to be the quantity of free and hydrolyzed formaldehyde extracted from the leather under standard conditions.
Note 2: This method is not absolutely selective for formaldehyde, because other chemicals such as dyes may interfere with the results.
4 Reagents and materials
Use only reagents of recognized analytical grade, unless otherwise stated. All solutions are aqueous solutions.
4.1 The water shall be Grade 3 in accordance with GB/T 6682.
4.2 Extraction solution, sodium dodecylsulfonate or sodium dodecylsulfate solution, 0,1 %, 1 g in 1,000 mL water.
4.3 Acetylacetone solution (Nessler's reagent), 150 g ammonium acetate + 3 mL glacial acetic acid + 2 mL acetylacetone (CAS 123-54-6) in 1,000 mL water, and shall be stored at low temperature and away from light for at least 12 h before use
Note: The color of the Nessler's reagent will gradually darken within 12 h after the storage, and it is valid for 1 week under storage at 0℃ to 4℃ and away from light.
4.4 Ammonium acetate solution, 150 g ammonium acetate + 3 mL glacial acetic acid in 1,000 mL water.
4.5 Dimedone (5,5-dimethyl-1,3-cyclohexanedione, CAS 126-81-8) solution, 5 g dimedone 1) 1,000 mL of water. Prepare immediately before use.
Note: Dimedone cannot be readily dissolved in pure water. In such cases, it may be dissolved with a small amount of ethanol and diluted to 1,000 mL with distilled water.
5 Instruments and apparatus
5.1 Volumetric flasks of capacities 10 mL, 50 mL, and 1,000 mL.
5.2 Erlenmeyer flasks, of capacities 25 mL, 100 mL, and 250 mL.
5.3 Strainer with glass fibre filter, GF8 (or glass filter strainer G3, diameter 70 mm to 100 mm).
5.4 Water bath oscillator, frequency (50 ± 10) times/min
5.5 Thermometer, with 0.1 °C graduations over the range 10 °C to 50 °C.
5.6 Analytical balance, weighing to an accuracy of 0.1 mg.
5.7 Spectrophotometer, with suitable semi-micro cells capable of measuring absorbance at 412 nm. The recommended cell path length is 20 mm. To increase the sensibility, a semi-micro cell with 40 mm or 50 mm optical path length may be used.
6 Procedures
6.1 Sampling and preparation of specimens
6.1.1 Sampling
Leather is sampled in accordance with QB/T 2706, and fur is sampled in accordance with QB/T 1267.
If sampling in accordance with QB/T 2706 or QB/T 1267 is not possible (e.g. leathers from finished products like shoes, garments), provide details about sampling together with the test report.
6.1.2 Preparation of specimens
Leather specimens shall be prepared in accordance with QB/T 2716.
Fur specimens shall be prepared in accordance with QB/T 1272. During the preparation, fur samples shall be kept intact as far as possible and avoid any damage.
6.2 Extraction
Weigh approximately (2.0 ± 0.1) g of leather pieces to the nearest 0.01 g into a 100 mL glass Erlenmeyer flask (5.2). Add 50 mL of extract solution (4.2) (previously preheated at 40 °C) and fit the Erlenmeyer flask with a glass stopper. Shake the contents of the flask in the water bath oscillator (5.4) for (60 ± 2) min at (40 ± 1) °C. Immediately filter the warm extract by vacuum (use not less than 5 kPa) through a strainer with glass fibre filter (5.3) into a flask. Cool the filtrate, in a closed flask, down to room temperature (18 °C to 26 °C).
Note: Do not modify the specimen/ solution ratio. Extraction and analysis shall be performed within the same working day.
6.3 Reaction with acetylacetone
Pipette 5 mL of the filtrate (6.2) into a 25 mL Erlenmeyer flask (5.2) and add 5 mL of acetylacetone solution (4.3). Fit the Erlenmeyer flask with a glass stopper. Stir the solution for (30 ± 1) min at a temperature of (40 ± 1) °C. Cool the solution in the dark for at least 30 min to a temperature (18 °C to 26 °C) then measure the absorbance spectrophotometrically at 412 nm against a blank solution made from a mixture of 5 mL extraction solution (4.2) plus 5 mL acetylacetone solution (4.3). Register the absorbance obtained as Ep. The maximum time between the end of the color development reaction and the measure of the absorbance shall be 1 h.
For the purpose of determining the absorbance resulting from the initial color of the filtrate (6.2), pipette 5 mL of the filtrate into a 25 mL Erlenmeyer flask (5.2) and add 5 mL of ammonium acetate solution (4.4). Thereafter, the same method is applied as with the specimen. Register the absorbance obtained as Ee.
Note: For a high content of formaldehyde (>100 mg/kg), the weighing amount of specimens or the pipetting amount of the filtrate may be reduced. For pipetted filtrate less than 5 mL, make it up to 5 mL with distilled water (by diluting).
6.4 Checking acetylacetone for absence of formaldehyde
In order to check that the acetylacetone solution does not contain formaldehyde, measure 5 mL extraction solution (4.2) plus 5 mL acetylacetone solution (4.3), using 5 mL of extraction solution (4.2) plus 5 mL of water as the reference. The measured absorbance shall not be larger than 0.025 when measured in a 20 mm cell at 412 nm, 0.063 when measured in a 50 mm cell at 412 nm or 0.050 when measured in a 40 mm cell at 412 nm.
Foreword i
1 Scope
2 Normative references
3 Principle
4 Reagents and materials
5 Instruments and apparatus
6 Procedures
7 Expression of results
8 Test report
Annex A (Informative) Structural changes of this part with respect to ISO 17226-2:
Annex B (Informative) Technical differences between this part and ISO 17226-2: 2018 and their causes
Annex C (Normative) Determination of formaldehyde content in stock solution
