Detail of GB 31604.32-2016

Introduction of GB 31604.32-2016

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. This standard replaces the determination of sulfur dioxide in SN/T 2827-2011 Food Contact Materials for Export - Wood Materials - Determination of Sulfur Dioxide. The following changes have been made with respect to SN/T 2827-2011: ——This standard is renamed as "National Food Safety Standard - Food Contact Materials and Articles - Determination of Sulfur Dioxide in Wood Materials"; ——The "Method Summary" in Method I is revised as "Principle"; ——The "Result Calculation and Expression" in Method I is revised as "Expression of Analysis Results"; ——The calculation formula of Method I is modified; ——The "Method Summary" in Method II is revised as "Principle", and the text content are revised; ——The "Result Calculation and Expression" in Method II is revised as "Expression of Analysis Results", and the text content are revised. National Food Safety Standard Food Contact Materials and Articles Determination of Sulfur Dioxide in Wood Materials 1 Scope This standard specifies determination methods, i.e., titrimetric method and colorimetry, of sulfur dioxide in food contact wood (bamboo) materials. This standard is applicable to determination of sulfur dioxide in chopsticks, bowls, spoons and spatula which are made of wood (bamboo). Method I Titration 2 Principle Acidize, heat and distill the specimen in closed container to release the sulfur dioxide in it, then absorb the released substance with lead acetate solution. After absorption, acidize with concentrated hydrochloric acid, carry out titration with iodum standard solution, then work out the sulfur dioxide content in the specimen according to the amount of the consumed iodum standard solution. 3 Reagents and Materials Unless otherwise specified, analytically-pure reagents and Class-III water (defined in GB/T 6682) are adopted for the purpose of this method. 3.1 Reagents 3.1.1 Hydrochloric acid (HCl). 3.1.2 Lead acetate [Pb(CH3COO)2·3H2O]. 3.1.3 Iodine (I2). 3.1.4 Soluble starch [(C6H10O5)n]. 3.2 Preparation of reagents 3.2.1 Hydrochloric acid solution (1+1, volume ratio): take 100mL of hydrochloric acid, carefully add it into 100mL of water, then mix uniformly. 3.2.2 Lead acetate solution (20g/L): weigh 2g of lead acetate, dissolve it with a small amount of water and dilute to 1,000mL. 3.2.3 Starch indicator (10g/L): weigh 1g of soluble starch, mix it with a small amount of water till it turns into paste; slowly pour 100ml of boiling water into it, stir the paste while adding the water, boil it for 2min and cool it to ambient temperature for standby; this solution shall be prepared immediately before use. 3.3 Standard product Iodine standard solution [( I2)=0.1 mol/L]: marketable products or those prepared and calibrated according to GB/T 601 shall be adopted. 3.4 Preparation of standard solutions Standard volumetric solution of iodine [( I2)=0.01mol/L]: pipet 10.0mL of iodine standard solution, pour it into a 100mL volumetric flask, then dilute it with water and scale the volume to the scale. 4 Instruments and Apparatus 4.1 Analytical balance: with sensitivity of 0.1mg. 4.2 All-glass distiller. 4.3 Acid burette. 4.4 Iodine flask. 4.5 Electric plane or electric saw. 4.6 Grinder. 5 Analysis Steps 5.1 Preparation of specimen Take the surface part (thickness: 3mm) of the sample taken with electric plane or electric saw, grind it and load it into a clean container. Seal the container and use the content as the specimen; mark it well. During sample preparation, the sample shall be protected from the contamination of sulfur dioxide. 5.2 Distillation Weigh 5g (accurate to 0.01g) of the specimen and place it into a 500mL round-bottom flask. Add 250mL of water into the round-bottom flask, during which a small amount of glass beads may be added into to prevent the bumping of sample solution. Mount the condensing unit and insert the lower end of the condenser tube below the liquid level of the 25mL lead acetate solution (20g/L) contained in the iodine flask; add 10mL of hydrochloric acid solution (1+1, volume ratio) into the distillation flask, immediately cover the flask with the stopper, then heat and distill it. Move the lower end of the condenser tube away from the liquid level when the distillate reaches about 200mL, then distill it for another 1min. Wash the part of the device inserted into lead acetate solution (20 g/L) with a small amount of distilled water. Carry out blank test while testing the specimen, and carry out the determination of blank test from the step "Add 250mL of water into the round-bottom flask". 5.3 Titration Add 10mL of hydrochloric acid and 1mL of starch indicator (10g/L) successively into the iodine flask which is already taken down, shake well, then carry out titration with standard volumetric solution of iodine (0.01mol/L) until the solution turns blue and the blue color persists for 30s without fading. 6 Expression of Analysis Results The content of sulfur dioxide in the specimen shall be calculated according to Formula (1): (1) Where, X——the content of sulfur dioxide in the specimen, mg/kg; V1——the volume of iodine standard volumetric solution used for the titration of specimen, mL; V2——the volume of iodine standard volumetric solution used for the titration of reagent blank, mL; c——the concentration of iodine standard titration solution, mol/L; 0.032——the mass of sulfur dioxide equivalent to 1mL of iodine standard solution [( I2)=1.0 mol/L], g/mol; 1,000——the conversion coefficient; m——the mass of specimen, g; The calculation result is accurate to three significant figures. 7 Accuracy The absolute difference of results from two independent determinations under repeatability condition shall not exceed 10% of their arithmetic average. 8 Others As for this method, the detection limit is 10mg/kg. Method II Colorimetry 9 Principle Acidize, heat and distill the specimen in a closed container to release the sulfur dioxide contained in it; the sulfur dioxide will be absorbed by potassium mercuric tetrachloride and forms stable complexes which will then reacts with formaldehyde and pararosaniline chloride to generate rose purple compounds. Carry out quantitative determination by colorimetry.

Contents of GB 31604.32-2016

Foreword i 1 Scope 2 Principle 3 Reagents and Materials 4 Instruments and Apparatus 5 Analysis Steps 6 Expression of Analysis Results 7 Accuracy 8 Others 9 Principle 10 Reagents and Materials 11 Instruments and Apparatus 12 Analysis Steps 13 Expression of Analysis Results 14 Accuracy 15 Others Annex A Preparation of Sulfur Dioxide Standard Solution