This standard supersedes “Determination of Sulphite in Foods” (GB/T 5009.34-2003).
Compared with GB/T 5009.34-2003, this standard has the following main modifications:
- The standard name is revised as "National Food Safety Standard - Determination of Sulfur Dioxide in Foods";；
- Method I and Appendix A are deleted;
- The original Method II - distillation method is modified to titration method.
National Food Safety Standard
Determination of Sulfur Dioxide in Foods
食品安全国家标准
食品中二氧化硫的测定
1 Scope
This standard specifies the determination method of total sulfur dioxide in such foods as preserved fruits, dried vegetables, rice noodles, vermicelli, granulated sugar, edible mushrooms and wine.
This standard is applicable to the determination of total sulfur dioxide in such foods as preserved fruits, dried vegetables, rice noodles, vermicelli, granulated sugar, edible mushrooms and wine.
2 Principle
Acidize and distill the sample in a sealed container, absorb the distillate with lead acetate solution, acidize the absorbed solution with hydrochloric acid, titrate with iodine standard solution and calculate the content of sulfur dioxide in the sample according to the consumption of the iodine 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 Sulfuric acid (H2SO4).
3.1.3 Soluble starch [(C6H10O5)n].
3.1.4 Sodium hydroxide (NaOH).
3.1.5 Sodium carbonate (Na2CO3).
3.1.6 Lead acetate (C4H6O4Pb).
3.1.7 Sodium thiosulfate (Na2S2O3·5H2O) or anhydrous sodium thiosulfate (Na2S2O3).
3.1.8 Iodine (I2).
3.1.9 Kalium iodide (KI).
3.2 Preparation of reagents
3.2.1 Hydrochloric acid solution (1+1): measure 50mL hydrochloric acid, slowly pour it into 50mL water, and stir while adding.
3.2.2 Sulfuric acid solution (1+9): measure 10mL sulfuric acid, slowly pour it into 90mL water, and stir while adding.
3.2.3 Starch indicating liquid (10g/L): weigh 1g soluble starch, blend it with a little amount of water into a paste and then pour it slowly into 100mL boiling water, stir while adding, boil it for 2min and cool for use; this solution shall be used immediately upon preparation.
3.2.4 Lead acetate solution (20g/L): weigh 2g lead acetate and dissolve in a small amount of water and dilute to 100mL.
3.3 Standard products
Potassium dichromate (K2Cr2O7), guaranteed reagent, with the purity greater than or equal to 99%.
3.4 Preparation of standard solution
3.4.1 Sodium thiosulfate standard solution (0.1mol/L): weigh 25g sodium thiosulfate containing crystal water or 16g anhydrous sodium thiosulfate, dissolve in 1000mL newly-boiled and cooled water, add 0.4g sodium hydroxide or 0.2g sodium carbonate, shake well, store in a brown bottle, filter it after being kept for two weeks, and calibrate its accurate concentration with potassium dichromate standard solution. Alternatively, purchase certificated sodium thiosulfate standard solution.
3.4.2 Iodine standard solution [c(1/2 I2)=0.10mol/L]: weigh 13g iodide and 35g kalium iodide, add about 100mL water, add 3 drops of hydrochloric acid after dissolution, dilute with water to 1000mL, transfer to a brown bottle after filtration. Calibrate with sodium thiosulfate standard solution prior to use.
3.4.3 Potassium dichromate standard solution [c(1/6K2Cr2O7)=0.1000mol/L]: accurately weigh 4.9031g potassium dichromate already dried to constant weight in a 120±2℃ electric dry oven, dissolve in water and transfer to a 1000mL volumetric flask and scale the volume to the scale. Alternatively, purchase certificated potassium dichromate standard solution.
3.4.4 Iodine standard solution [c(1/2 I2)=0.01000mol/L]: dilute 0.1000mol/L iodine standard solution with water by 10 times.
Foreword I
1 Scope
2 Principle
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Result
7 Precision
8 Other
