Detection of ferrous gluconate as a food additive

A. General regulations

The reagents and water used in this standard, unless otherwise specified, refer to analytical pure reagents and Grade III water specified in GB/T6682. The standard solutions used in the experiment, impurity determination standard solutions, preparations and their products, unless other requirements are specified, shall be prepared in accordance with the provisions of GB/T601, GB/T602, and GB/T603. The solution used in the experiment refers to aqueous solution when no specific solvent is specified for preparation

A.2 Identification Test

A.2.1 Reagents and Materials

A.2.1.1  Glacial acetic acid

A.2.1.2; Ethanol

A.2.1.3; Phenylhydrazine

A.2.1.4; Potassium ferrocyanide solution: 100g/L, prepared before use

A.2.2 Identification Method

A.2.2.1 Solubility

It is easily soluble in hot water and almost insoluble in ethanol

A.2.2.2 Identification of ferrous ions

Weigh approximately 0.5g of the sample, dissolve it in 100mL of water, and add potassium ferrocyanide solution dropwise to generate a dark blue precipitate.

A.2.2.3 Identification of Glucose

A.2.2.3.1 Method Summary

The sample is co heated with phenylhydrazine in acetic acid medium to generate yellow glucosyl phenylhydrazine crystals.

A.2.2.3.2 Analysis Steps

Weigh approximately 0.5g of the sample, add 10mL of water, dissolve (heat if necessary), take 5mL, add 0.7mL of glacial acetic acid and 1mL of freshly distilled phenylhydrazine, heat on a water bath for 30min, and let it reach room temperature. Rub the inner wall of the test tube with a glass rod to precipitate yellow crystals.

A.3; Determination of ferrous gluconate (C12H22FeO14) content (on a dry basis)

A.3.1 Method Summary

In an acidic medium, titrate with cerium sulfate standard titration solution, and indicate the endpoint with 1,10-phenanthroline indicator solution

A.3.2 Reagents and Materials

A.3.2.1 Zinc Powder

A.3.2.2; Sulfuric acid

A.3.2.3 Sulfuric acid solution: Measure 60mL of sulfuric acid, slowly inject 1000mL of water, cool, and shake well

A.3.2.4; Cerium sulfate standard titration solution: c (CeSO4)=0.1mol/L

A.3.2.5 1,10-phenanthroline indicator solution: Weigh 0.5g of ferrous sulfate, dissolve in 100mL of water, add 2 drops of sulfuric acid solution and 0.5g of 1,10-phenanthroline, shake well, and store the solution in a closed container

A.3.3 Analysis Steps

Weigh approximately 1.5g of the sample, accurate to 0.0001g, and place it in a 500mL conical flask. Dissolve in 75mL of water and 15mL of sulfuric acid solution, and add 250mg of zinc powder until the solution decolors. Cover the conical flask with a small beaker and let it stand at room temperature for 20min. Filter (or vacuum filter) with a vertically fused glass funnel covered with a thin layer of zinc powder on the surface. Wash the vertically fused glass funnel with 10mL of sulfuric acid solution and 10mL of water, merge the filtrate and washing solution, and use 1,10-phenanthroline indicator solution as the indicator. Quickly titrate with cerium sulfate standard titration solution until the color of the solution changes from orange to green. Simultaneously conduct a blank test

A.3.4 Result Calculation

The mass fraction w1 of ferrous gluconate (C12H22FeO14) content (calculated on a dry basis) is calculated according to equation (A.1):

In the equation:

V1- the volume of cerium sulfate standard titration solution consumed in the titration sample solution, in milliliters (mL)

V0- Volume of cerium sulfate standard titration solution consumed for titration of blank solution, in milliliters (mL)

1000- conversion coefficient

c1- concentration of cerium sulfate standard titration solution, in moles per liter (mol/L)

M1- Molar mass of ferrous gluconate, in grams per mole (g/mol), [M1 (C12H22FeO14)=446.15]

m1- mass of the sample, in grams (g)

w2- The mass fraction of the measured sample drying loss,%

Take the arithmetic mean of the results of two parallel measurements as the standard. The absolute difference between the results of two parallel measurements shall not exceed 0.3%

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