Food additive - Potassium stearate detection

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A. 1 General regulations

Unless otherwise specified in this standard, the purity of the reagents used should be above analytical purity. The standard titration solution used, the standard solution for impurity determination, the formulation, and the product should be prepared in accordance with the provisions of GB/T601, GB/T602, and GB/T603. The test water should comply with the provisions of Grade III water in GB/T6682. 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 Solubility test

The sample is soluble in water and ethanol.

A.2.2 Identification of Potassium Ions

Take 1g of the sample, add a mixed solution consisting of 25mL of water and 5mL of hydrochloric acid, and heat it.

. Fatty acids are released and float on the liquid surface, soluble in n-hexane. After cooling, pour the liquid phase layer into the flask and evaporate until dry. Dissolve the residue in water. Take the platinum wire, wet it with hydrochloric acid solution, dip it in the sample, and burn it in a colorless flame, the flame will turn purple; But when there is a small amount of sodium salt mixed, it should be identified through blue glass fluoroscopy

A.3; Determination of potassium stearate content

A.3.1 Analysis steps

A.3.1.1 Preparation of methyl stearate

The sample is pre dried to constant weight at 105 ℃± 2 ℃. Accurately weigh approximately 350mg of the dried sample and perform methylation according to the method specified in GB/T17376 to obtain methyl stearate

A.3.1.2 Gas Chromatography Analysis

Perform gas chromatography analysis on methyl stearate (A.3.1.1) according to the method specified in GB/T17377, and calculate the mass fraction of potassium stearate.

A.4 Determination of free fatty acids

A.4.1 Reagents and solutions

A.4.1.1  Sodium hydroxide standard titration solution: c (NaOH)=0.1mol/L

A.4.1.2 95% ethanol: Use phenolphthalein as the indicator solution and neutralize with sodium hydroxide solution until light pink

A.4.1.3 Phenolphthalein indicator solution: 10g/L

A.4.2 Analysis Steps

Weigh 7g to 28g of the sample, accurate to 0.001g, place it in a conical flask, add 50mL of 95% ethanol, heat to dissolve it.

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

A.4.3 Result Calculation

The mass fraction w1 of free fatty acids is calculated according to equation (A.1):

In the equation:

V - the volume of the sodium hydroxide standard titration solution used, in milliliters (mL)

c - The actual concentration of the sodium hydroxide standard titration solution used, in moles per liter (mol/L)

32.2- conversion factor

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

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