Food additive - Glycerol octoate detection

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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/T6682-2008. The standard titration solution used in the analysis, the standard solution used for impurity determination, the formulation, and the product shall be prepared in accordance with the provisions of GB/T601, GB/T602, and GB/T603 unless other requirements are specified. The solution used in the analysis refers to aqueous solution when no specific solvent is specified for preparation

A.2 Determination of Iodine Value

A.2.1 Reagents and Materials

A.2.1.1  Acetic acid

A.2.1.2 Iodine

A.2.1.3 Chlorine gas

A.2.1.4; Cyclohexane acetic acid mixture: 1+1

A.2.1.5; Potassium iodide solution: 150g/L

A.2.1.6 Starch indicator solution: 10g/L

A.2.1.7; Sodium thiosulfate standard titration solution: c (Na2S2O3)=0.1mol/L

A.2.1.8; Iodine chloride solution (Wechsler solution):

Dissolve 13g of iodine in 1000mL of acetic acid (slightly heated during dissolution), then place it in a 1000mL brown bottle and cool. This is the iodine solution. Measure 100mL-200mL into another brown bottle and place in a shaded area for adjustment. Inject chlorine gas into the remaining 800mL-900mL iodine solution until the solution gradually fades from dark color to orange red transparency. After correcting the chlorine gas intake according to the calibration method, adjust it with a pre retained iodine solution

Calibration method: Take 20.0mL of iodine solution and newly prepared iodine chloride solution (Webster's solution), add 20mL of potassium iodide solution, and then add 100mL of water to each solution. Titrate with 0.1mol/L sodium thiosulfate standard titration solution until the solution turns light yellow, add 1mL of starch indicator solution, and continue titration until the blue color disappears. The volume of the sodium thiosulfate standard titration solution consumed by the newly prepared Webster solution should be close to twice that of the actual solution

A.2.2 Analysis Steps

Weigh 2g to 3g of the sample, accurate to 0.001g, place it in an iodine volumetric flask, and add 20mL of cyclohexane acetic acid mixture.

. After the test sample is dissolved, add 25.0mL of Webster's solution with a pipette, shake well, and store in a dark place at around 25 ℃ for 30 minutes. Then remove the iodine volumetric flask from the dark, add 20mL of potassium iodide solution, and then add 100mL of water. Titrate with sodium thiosulfate standard titration solution while shaking until the solution turns pale yellow. Add 1mL of starch indicator solution and continue titrating until the blue color disappears. Simultaneously conduct a blank test

A.2.3 Result Calculation

The iodine value is calculated as the mass fraction w1, and the value is expressed in grams per hundred grams (g/100g). Calculate according to formula (A.1):

In the formula:

V1- the volume of sodium thiosulfate standard titration solution consumed in the blank test, in milliliters (mL)

V2- The volume of sodium thiosulfate standard titration solution consumed by the sample, in milliliters (mL)

C1- The accurate value of the concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L)

0.1269- The numerical value of the millimolar mass of iodine atoms, in grams per millimole (g/mmol) [M (I)=126.9]

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

100- Mass conversion coefficient

The experimental results shall be based on the arithmetic mean of the parallel measurement results. The absolute difference between two independent test results obtained under repeatability conditions shall not exceed 0.05g/100g, provided that the difference does not exceed 5% when greater than 0.05g/100g

A.3 Determination of Acid Value

A.3.1 Reagents and Materials

A.3.1.1  Potassium hydroxide ethanol standard titration solution: c (KOH)=0.1mol/L

A.3.1.2 95% ethanol: Use phenolphthalein as an indicator and neutralize with potassium hydroxide solution until light pink

A.3.1.3 Phenolphthalein indicator solution: 10g/L

A.3.2 Analysis Steps

Weigh 15g of the sample to the nearest 0.0001g, place it in a conical flask, add about 100mL of 95% ethanol, and heat it to dissolve.

. Add about 6 drops of phenolphthalein indicator solution, immediately titrate with potassium hydroxide ethanol standard titration solution until it turns pale pink, and maintain it for 30 seconds without fading as the endpoint

A.3.3 Result Calculation

The acid value is calculated as the mass fraction W2 of potassium hydroxide (KOH), and the value is expressed in milligrams per gram (mg/g). Calculate according to formula (A.2):

In the formula:

V3- the volume of potassium hydroxide ethanol standard titration solution consumed by the sample, with the unit being milliliters (mL)

C2- The accurate value of the concentration of potassium hydroxide ethanol standard titration solution, in moles per liter (mol/L)

56.1- The numerical value of the molar mass of potassium hydroxide, in milligrams per millimole (mg/mmol)

m2- The numerical value of the sample mass, in grams (g)

The experimental results shall be based on the arithmetic mean of the parallel measurement results. The absolute difference between two independent test results obtained under repeatability conditions shall not exceed 0.01mg/g

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