GB 5009.43-2016National Food Safety Standard -- Determination of sodium glutamate in monosodium glutamate (English PDF)

3.1 Reagents

3.1.1 Formic acid (CH2O2).

3.1.2 Acetic acid (C2H4O2).

3.1.3 alpha-Naphthol phenylmethanol (C27H18O2).

3.2 Preparation for reagent

alpha-naphthol phenylmethanol-acetic acid indicator solution (2g/L). weigh and take 0.1g of alpha-naphthol phenylmethanol; use acetic acid (3.1.2) to dissolve it; dilute it to 50mL.

3.3 Standard products

Perchloric acid (HClO4).

3.4 Preparation for standard solution

Perchloric acid standard titration solution [c(HClO4) = 0.1mol/L]. according to GB/T 601, prepare and calibrate it.

4.2 Non-aqueous pH electrode regards Ag/AgCl as internal reference electrode; the

internal reference electrolyte shall be 2mol/L lithium chloride ethanol solution OR

0.4mol/L tetraethylammonium bromide ethylene glycol solution.

4.3 Magnetic stirrer.

4.4 Analytical balance. the sensitivity is 0.1mg.

4.5 Ultrasonic cleaner.

5.1 Preparation for samples

Weigh and take 0.15g (accurate to 0.0001g) of the sample which has been ground into fine particles; place it into a 100mL beaker; add 3mL of formic acid (3.1.1); sonicate it until it is completely dissolved; then, add 40 mL of acetic acid (3.1.2); shake it evenly.

5.2 Determination of sample

5.2.1 Determination by potentiometric titration method

5.2.1.1 Reference conditions for the determination of sample.

a) The determination of sample adopts dynamic titration mode OR equal titration mode;

b) Blank determination of reagents. adopt equivalent titration mode. Minimum are obtained under repeatability conditions shall not exceed 0.5g/100g.

Second Method – Optical Rotation Method

11.1 Preparation for samples

Weigh and take 10g of the sample (accurate to 0.0001g); add small amount of water to dissolve it; transfer it to a 100mL volumetric flask; add 20mL of hydrochloric acid;

mix it AND cool it to 20 °C; set it to constant volume; shake it evenly.

11.2 Determination of sample solution

At 20°C, use the standard optical rotation angle to calibrate the instrument; place the test solution of 11.1 in the optical rotation tube (There shall be no air bubbles); observe its optical rotation; at the same time, record the temperature of the sample solution in optical rotation tube.

17.2 Determination of sample solution

Turn on the magnetic stirrer; use sodium-hydroxide standard solution to titrate until that the acidometer indicates “pH 8.2”; record the milliliters of the consumed sodium- hydroxide standard titration solution; calculate the content of the total acid.

Add 10.0 mL of formaldehyde solution; mix it evenly; use sodium-hydroxide standard solution to titrate until that the acidometer indicates “pH 9.6”; record the milliliters of the consumed sodium-hydroxide standard titration solution.

Meanwhile, take 60mL of water; firstly, use sodium-hydroxide standard solution to adjust it to “pH 8.2”; then, add 10.0mL of formaldehyde solution; use sodium hydroxide standard solution to titrate it until pH 9.6; make reagent’s blank test.