1 Scope
This standard specifies the method for determination of hydrogen peroxide residual quantity in foods.
This standard is applicable to the determination of hydrogen peroxide residual quantity in foods such as prepackaged milk, beverages, bean products, waterishlogged food, chicken feet, etc.
Method I Iodometric Method
2 Principle
The strong oxide in foods will oxidize the kalium iodide in dilute sulphuric acid to produce certain amount of iodine with starch as indicator. Obtain the total amount of the strong oxide by titration with sodium thiosulfate standard solution. Add into catalase to dissolve and remove the hydrogen peroxide in the specimen, and then titrate with thiosulfuric acid standard solution to determine the content of the rest oxide. The content of hydrogen peroxide in the sample may be obtained by calculating the difference between two titration results.
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 Sodium thiosulfate (Na2S2O3).
3.1.2 Soluble starch [(C6H10O5)n].
3.1.3 Kalium iodide (KI).
3.1.4 Sulfuric acid (H2SO4).
3.1.5 Ammonium molybdate [(NH4)6Mo7O24·4H2O].
3.1.6 Catalase (unit activity larger than 200,000/ mL): preserved at -20℃.
3.1.7 Potassium ferrocyanide {K4[Fe(CN)6]·3H2O}.
3.1.8 Zinc acetate (C4H6O4Zn·2H2O).
3.1.9 Acetic acid (C2H4O2).
3.1.10 Activated carbon.
3.2 Reagent preparation
3.2.1 Starch indicator (10g/L): weigh 0.50 g soluble starch and mix with a small amount of water into paste, then pour it into 50mL boiling water to mix up and boil. Prepare immediately before use.
3.2.2 Kalium iodide solution (100g/L): weigh 10.00g kalium iodide, dissolve it with water and scale the volume to 100mL, then store it in a brown bottle. Prepare immediately before use.
3.2.3 10% sulfuric acid solution (mass fraction): measure 60mL sulfuric acid and inject it slowly into the water (about 700 mL); after it cools down, dilute it to 1,000mL.
3.2.4 3% ammonium molybdate solution: weigh 3.00g ammonium molybdate and dissolve with 100mL water.
3.2.5 0.1 % catalase solution: weigh 0.10g catalase and dissolve it with 100mL distilled water by several times. It may be preserved for two months by cold storage.
3.2.6 Potassium ferrocyanide solution: weigh 106.0 g potassium ferrocyanide, add in water to dissolve and dilute the solution to 1,000mL.
3.2.7 Zinc acetate solution: weigh 220.0g zinc acetate, add into 30mL acetic acid and then dissolve with water and dilute it to 1,000mL.
3.2.8 Activated carbon: add 100g activated carbon to 750mL hydrochloric acid (1mol/L), leaving it backflowing for 1~2h, then filter it, and wash it with water for several times until no ferric ions (Fe3+) are available in the filtrate, after which place the carbon into 110℃ oven for bake out.
Note: Method to inspect ferric ion: with the help of prussian blue reaction. Mix 20g/L potassium ferrocyanide with 1% hydrochloric acid in an equivalence, then drop the eluted filtrate into the solution, and blue precipitation will be produced if there is any ferric ion.
3.3 Preparation of standard solution
3.3.1 0.1 mol/L sodium thiosulfate standard stock solution: prepare and calibrate according to the method specified in GB/T 601.
3.3.2 0.0020 mol/L sodium thiosulfate standard working solution: dilute the standard stock solution right before use.
4 Instruments and Apparatus
4.1 Electronic balance: with the sensibility of 0.01 g.
4.2 High-speed triturator.
5 Analysis Steps
5.1 Preparation of specimen
5.1.1 Solid sample
Weigh 10g edible part of the evenly-smashed specimen (to the accuracy of 0.01 g), add proper amount of water to dissolve, and transfer it to 100mL volumetric flask. As for the samples with high protein and fat content, add into 5mL zinc acetate solution, 5mL potassium ferrocyanide solution and water to scale the volume to the scale (V1) and shake well. After 30min of soaking, filter with filter paper with the filtrate as specimen solution for future use.
5.1.2 Liquid sample
Weigh 25g specimen (to the accuracy of 0.01 g) and put it into 100mL volumetric flask. As for the samples with high protein and fat content, add into 5mL zinc acetate solution, 5mL potassium ferrocyanide solution and water to scale the volume to the scale (V1) and shake well. After 30min of soaking, filter with filter paper with the filtrate as specimen solution for future use. If the sample filtrate is pigmented, add into 1g activated carbon and shake for 1 min, then filter with dry filter paper, the filtrate of which is for future use with the original filtrate discarded.
5.2 Determination
Pipet 25.0 mL filtrate (V2) respectively and put them into 250 iodine flasks A and B, with 0.5 mL catalase (0.1 %) added into A. Cover them and mix well, set them for 10 min (shake several times during setting). Add 5.0 mL sulfuric acid solution(10%), 5.0 mL kalium iodide solution and three drops of ammonium molybdate solution (3%) into flasks A and B respectively, mix well and set them in dark place for 10 min. Add 50mL water into both of them and titrate with sodium thiosulfate standard solution until the solution becomes light yellow, at which time add into 0.5 mL starch indicator and continue to titrate until the blueness disappears, with the consumption of sodium thiosulfate standard solution in flasks A and B recorded in milliliter.
6 Expression of Analysis Results
The content of hydrogen peroxide in the specimen shall be calculated according to Formula (1):
(1)
Where,
X——the content of hydrogen peroxide in the sample, mg/kg;
VB——the volume of standard volumetric solution of sodium thiosulfate consumed in flask B, mL;
VA——the volume of standard volumetric solution of sodium thiosulfate consumed in flask A, mL;
c——the concentration standard volumetric solution of sodium thiosulfate, mol/L;
V1——the total volume of the sample treatment fluid, mL;
17.01——the mass of hydrogen peroxide that is equivalent to 1.00 mL sodium thiosulfate standard solution [c(Na2S2O3) =1.000mol/L], mg;
m——the mass of the specimen, g.
V2——the volume of sample solution for determination, mL;
1000——the conversion coefficient.
The calculation results shall be expressed by the arithmetic mean value of the results from two independent determinations under repeatability condition, and three significant figures shall be retained.
Foreword i
1 Scope
Method I Iodometric Method
2 Principle
3 Reagents and Materials
4 Instruments and Apparatus
5 Analysis Steps
6 Expression of Analysis Results
7 Precision
8 Others
Method II Titanium Sulfate Spectrophotometric Method
9 Principle
10 Reagents and Materials
11 Instruments and Apparatus
12 Analysis Steps
13 Expression of Analysis Results
14 Precision
15 Others
