Food additive sulfuric acid testing

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A. 1 Warning

The samples in this standard have strong corrosiveness, and some reagents used in the inspection method are toxic or corrosive. Appropriate ammonium and protective measures should be taken during operation

A.2 General Provisions

When no other requirements are specified, the reagents and water used in this standard refer to analytical pure reagents and Grade III water specified in GB/T6682-2008.

. The standard titration solution, impurity determination standard solution, formulation, and product used in the experiment shall be prepared in accordance with the provisions of GB/601, GB/T602, and GB/T603 unless otherwise specified. When the solvent used for preparation is not specified, it refers to aqueous solution

A.3 Identification Test

A.3.1 Reagents and Materials

A.3.1.1  Barium chloride solution: 100g/L

A.3.1.2  Hydrochloric acid solution: 1+1

A.3.1.3; Lead acetate solution: 80g/L

A.3.1.4; Ammonium acetate solution: 100g/L

A.3.2 Identification method

A.3.2.1 Take approximately 1g of the sample, dissolve it in 20mL of water, and add barium chloride solution to produce a white precipitate that is insoluble in hydrochloric acid solution

A.3.2.2 Take approximately 1g of the sample and dissolve it in 20mL of water. Add lead acetate solution to produce a white precipitate, which is soluble in ammonium acetate solution

A.3.2.3 Take approximately 1g of the sample and dissolve it in 20mL of water. Add hydrochloric acid without precipitation

A.4 Determination of Sulfuric Acid (H2SO4) Content

A.4.1 Method Summary

Titrate the sample solution with a sodium hydroxide standard titration solution, and determine the sulfuric acid content based on the consumption of the sodium hydroxide standard titration solution.

A.4.2 Reagents; Sodium hydroxide standard titration solution: c (NaOH)=1mol/L

A.4.2.2 Methyl red indicator solution: 1g/L

A.4.3 Analysis Steps

Take approximately 1mL of the sample and place it in a known mass small conical flask with a stopper. Accurately weigh its mass to the nearest 0.0002g. Carefully add 30mL of water, cool it, and then add 2 drops of methyl orange indicator solution. Titrate with sodium hydroxide standard titration solution until yellow.

Perform a blank test simultaneously. The blank test, except for the absence of a sample, involves the same operations and types and amounts of reagents added (except for standard titration solutions) as the determination test

A.4.4 Result Calculation

The mass fraction w1 of sulfuric acid (H2SO4) content is calculated according to equation (A.1)

In the equation:

V - The volume of sodium hydroxide standard titration solution consumed for titrating the sample solution, in milliliters (mL)

V0- The volume of sodium hydroxide standard titration solution consumed for titrating the blank sample solution, in milliliters (mL)

C - The accurate value of the concentration of sodium hydroxide standard titration solution, in moles per liter (mol/L)

m - The numerical value of the mass of the sample, in grams (g)

1000- conversion factor

M - The numerical value of the molar mass of sulfuric acid (1/2H2SO4), in grams per mole (g/mol) (M=49.04)

The experimental results shall be based on the arithmetic mean of the parallel measurement results, and the absolute difference between the two independent measurement results obtained under repeatability conditions shall not exceed 0.2%

A.5; Determination of nitrate (calculated as NO3)

A.5.1 Reagents and materials

A.5.1.1 Sulfuric acid

A.5.1.2 Nitrate (NO3) standard solution: 0.100mg/mL

Weigh 8.022g of potassium nitrate that has been dried at 105 ℃± 2 ℃ for 1 hour, place it in a 500mL volumetric flask, dissolve it in water and dilute to the mark, and shake well. Transfer 5mL of this solution, insert a dropper below the 400mL sulfuric acid level, slowly drip in, and cool to room temperature. Transfer to a 500mL volumetric flask and dilute to the mark with sulfuric acid

A.5.1.3 Ferrous sulfate (FeSO4 · 7H2O) solution: 100g/L, ready to use

A.5.2 Analysis Steps

Transfer 50mL of sulfuric acid into two 100mL colorimetric tubes (A and B), slowly add 5mL of ferrous sulfate solution, stir evenly with a glass rod, and cool to 10 ℃~15 ℃ using an ice bath.

. Add 10mL of sample to the A colorimetric tube, cool to room temperature, and dilute to 100mL with sulfuric acid. Add 0.1mL of nitrate standard solution dropwise into the B colorimetric tube and mix well. Dilute with sulfuric acid to the mark. Observe the color of the solution in the A colorimetric tube from top to bottom against the color of the B colorimetric tube under a white luminescent background. The color presented by the A colorimetric tube should not be darker than the color presented by the B colorimetric tube

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