GB 5009.93-2017National food safety standard - Determination of selenium in foods (English PDF)

3.1 Reagents

3.1.1 Nitric acid (HNO3). excellent regent.

3.1.2 Perchloric acid (HClO4). excellent regent.

3.1.6 Sodium borohydride (NaBH4). excellent regent.

3.1.7 Potassium ferricyanide [K3Fe(CN)6].

3.2 Preparation of reagents

3.2.1 Nitric acid - perchloric acid mixed acid (9 + 1). MIX 900 mL of nitric acid with 100

mL of perchloric acid.

3.2.2 Sodium hydroxide solution (5 g/L). WEIGH 5 g of sodium hydroxide; DISSOLVE

in 1000 mL of water; MIX well.

3.3 Standard

Selenium standard solution. 1000 mg/L, or selenium standard solution at a certain concentration certified by the state and awarded the standard substance certificate.

3.4 Preparation of standard solutions

3.4.1 Selenium standard intermediate solution (100 mg/L). accurately PIPETTE 1.00

mL of selenium standard solution (1000 mg/L) in a 10 mL volumetric flask; ADD hydrochloric acid solution (5 + 95) to the mark; MIX well.

5.1 Sample preparation

NOTE. Sample contamination shall be avoided during sampling and preparation processes.

5.1.1 Cereal, bean samples

The sample, after the debris are removed and being crushed, is stored in plastic bottles.

5.2 Sample digestion

5.2.1 Wet digestion

WEIGH 0.5 g ~ 3 g (to the nearest 0.001 g) of solid sample or accurately PIPETTE 1.00 mL ~ 5.00 mL of liquid sample; PLACE in a conical flask; ADD 10 mL of nitric acid - perchloric acid mixed acid (9 + 1) and a few glass beads; COVER the surface dish for cold digestion overnight. The next day, HEAT on the electric hot plate, and timely ADD nitric acid. When the solution becomes clear and colorless and accompanied by white smoke, continue to HEAT until the remaining volume is about 2 mL.

5.2.2 Microwave digestion

WEIGH 0.2 g ~ 0.8 g (to the nearest 0.001 g) of solid sample or accurately PIPETTE 1.00 mL ~ 3.00 mL of liquid sample; PLACE in the digestive tube; ADD 10 mL of nitric acid and 2 mL of hydrogen peroxide; SHAKE to mix well. DIGEST in the microwave digestion instrument, and the recommended microwave digestion conditions are shown in Annex A (set digestion conditions according to different instruments).

5.3 Determination

5.3.1 Instrument reference conditions

Adjust the instruments to the best condition according to their performance. Reference conditions. negative high voltage 340 V; lamp current 100 mA; atomization temperature 800 °C; furnace height 8 mm; carrier gas flow rate 500 mL/min; shielding gas flow rate 1000 mL/min; standard curve method of measurement method; peak area of reading method; delay time 1 s; reading time 15 s; solution adding time 8 s;

sample injection volume 2 mL.

10.1 Reagents

10.1.1 Hydrochloric acid (HCl). excellent regent.

10.1.6 Cresol red (C21H18O5S).

10.1.7 Ammonia (NH3 - H2O). excellent regent.

10.2 Preparation of reagents

10.2.1 Hydrochloric acid solution (1 %). MEASURE 5 mL of hydrochloric acid; DILUTE

to 500 mL with water; MIX well.

10.2.4 Hydrochloric acid solution (6 mol/L). MEASURE 50 mL of hydrochloric acid;

slowly ADD to 40 mL of water; COOL; ADD water to 100 mL; MIX well.

10.2.5 Ammonia solution (1 + 1). MIX 5 mL of water with 5 mL of ammonia.

10.2.6 EDTA mixture.

10.3 Standard

Selenium standard solution. 1000 mg/L, or selenium standard solution at a certain concentration certified by the state and awarded the standard substance certificate.

10.4 Preparation of standard solutions

10.4.1 Selenium standard intermediate solution (100 mg/L). accurately PIPETTE 1.00

mL of selenium standard solution (1000 mg/L) in a 10 mL volumetric flask; DILUTE with hydrochloric acid solution (1 %) to the mark; MIX well.

10.4.2 Selenium standard use solution (50.0 µg/L). accurately PIPETTE 0.50 mL of selenium standard intermediate solution (100 mg/L); DILUTE with hydrochloric acid solution (1 %) to 1000 mL; MIX well.