GB 5413.18-2010National food safety standard -- Determination of vitamin C in foods for infants and young children, milk and milk products (English PDF)

4.1 Amylase. enzyme activity is 1.5U/mg; adjust the dosage in accordance

with the activity unit size.

4.2 Metaphosphoric acid-acetic acid solution A. weigh 15 g of metaphosphoric

acid and 40 mL of acetic acid (36%) in 200 mL of water; dissolve and dilute to

4.3 Metaphosphoric acid-acetic acid solution B. weigh 15 g of metaphosphoric

acid and 40 mL of acetic acid (36%) in 100 mL of water; dissolve and dilute to

4.5 Sodium acetate solution. use water to dissolve 500 g of sodium acetate

trihydrate till it is diluted to 1 L.

4.6 Boric acid-sodium acetate. weigh 3.0 g of boric acid; use the sodium

acetate solution (4.5) to dissolve till it is diluted to 100 mL; prepare when

required.

4.8 Vitamin C standard solution (100 µg/mL). weigh 0.050 g of Vitamin C

standard product; use metaphosphoric acid - acetic acid solution A (4.2) to

dissolve and make constant volume to 50 mL;

5.1 Fluorescence spectrophotometer.

5.2 Scale. inductance of 0.1 mg.

5.4 Incubator. 45°C±1°C.

6.1 Specimen Treatment

6.1.1 Starch-containing specimen. WEIGH about 5 g (accurate to 0.0001 g)

of well mixed or about 20 g (accurate to 0.0001 g) of liquid specimen

(containing about 2 mg of Vitamin C) in a 150 mL erlenmeyer flask.

6.1.2 Starch-free specimen. WEIGH about 5 g of well mixed solid specimen

(accurate to 0.0001 g). USE metaphosphoric acid-acetic acid A (4.2) to dissolve.

MAKE constant volume to 100 mL.

6.2 Preparation of solution for test

6.2.1 TRANSFER the aforementioned specimens (6.1.1, 6.1.2) and Vitamin

C standard solution (4.8) to a 250 mL erlenmeyer flask having about 2 g of

acidic activated carbon (4.4). Severely VIBRATE it. FILTER it (discard about 5

mL of initial filtration) and it shall be the filtration of specimen and standard

solution. Accurately PIPETTE 5.0 mL of the filtration of specimen and standard

solution. Respectively PLACE in the 25 mL and 50 mL flasks having 5.0 mL of

boric acid-sodium acetate solution (4.6). Place for 30 min. USE distilled water

for constant volume. Use it as the blank solution of specimen and standard

solution.

6.3 Determination

6.3.1 Drawing of standard curve

Immediately transfer the standard series of test solution (6.2.4) into the quartz

curette of the fluorescence spectrophotometer. Determine its fluorescence

value when excitation wavelength is 350 nm, emission wavelength is 430 nm.

Standard fluorescent value respectively minus standard blank fluorescence

value as Y-axis; take the corresponding vitamin C mass concentration as X-

coordinate to draw the standard curve.