GB 5009.12-2023National food safety standard - Determination of lead in foods (English PDF)

3.1 Reagents

3.1.1 Nitric acid (HNO3).

3.1.2 Perchloric acid (HClO4).

3.1.3 Ammonium dihydrogen phosphate (NH4H2PO4).

3.1.4 Palladium nitrate [Pd(NO3)2].

3.1.5 Ammonium acetate (CH3COONH4).

3.1.6 Sodium acetate (CH3COONa).

3.2 Preparation of reagents

3.2.1 Nitric acid solution (5+95). Measure 50 mL of nitric acid; slowly add it to 950

mL of water; mix well.

3.2.2 Nitric acid solution (1+9). Measure 50 mL of nitric acid; slowly add it to 450 mL

of water; mix well.

3.2.3 Nitric acid solution (1+99). Measure 10 mL of nitric acid; slowly add it to 990

mL of water; mix well.

3.2.4 Sodium acetate solution (2 mol/L). Weigh 164.0 g of sodium acetate; add water

to dissolve; adjust the volume to 1 000 mL.

3.2.5 Ammonium acetate solution (1 mol/L). Weigh 77.1 g of ammonium acetate; add

water to dissolve; adjust the volume to 1 000 mL.

3.2.6 Ammonium dihydrogen phosphate-palladium nitrate solution. Weigh 0.02 g of

palladium nitrate; add a small amount of nitric acid solution (1+9) to dissolve it; then,

add 2 g of ammonium dihydrogen phosphate; after dissolution, use nitric acid solution

(5+95) to adjust the volume to 100 mL; mix well.

3.3 Standard

Lead nitrate [Pb(NO3)2, CAS number. 10099-74-8]. purity >99.99%, or lead standard

solution certified by the state and granted with a reference material certificate.

3.4 Preparation of standard solution

4.1 Atomic absorption spectrometer. equipped with graphite furnace atomizer and

accompanied by lead hollow cathode lamp.

4.2 Analytical balance. The sensitivity is 0.1 mg and 1 mg, respectively.

4.5 Constant-temperature drying oven.

4.6 Pressure digestion tank. equipped with polytetrafluoroethylene digestion inner tank.

4.7 Solid-phase extraction column.

5.1 Sample preparation

5.1.1 Solid samples

5.1.2 Liquid samples

For samples of soft drinks, alcoholic beverages, condiments, etc., shake well.

5.1.3 Semi-solid samples

Mix well.

5.2 Sample pretreatment

5.3 Determination

5.3.1 Apparatus reference conditions

See Appendix C for apparatus reference conditions.

5.3.2 Preparation of standard curve

In order of mass concentration from low to high, add 10 µL of lead standard series

solution and 5 µL of ammonium dihydrogen phosphate-palladium nitrate solution (the

optimal injection volume and optimal matrix modifier can be determined according to

the instrument used, and samples passing through the solid-phase extraction column do

not need to be added with matrix modifier) into the graphite furnace at the same time,

and measure their absorbance values after atomization.

10.1 Reagents

10.1.1 Nitric acid (HNO3). guaranteed reagent.

10.1.2 Perchloric acid (HClO4). guaranteed reagent.

10.1.3 Ammonium sulfate [(NH4)2SO4].

10.1.4 Ammonium citrate [C6H5O7(NH4)3].

10.1.5 Bromothymol blue (C27H28O5SBr2).

10.1.6 Sodium diethyldithiocarbamate [DDTC, (C2H5)2NCSSNa.3H2O].

10.1.7 Ammonia (NH3.H2O). guaranteed reagent.

10.1.8 4-Methyl-2-pentanone (MIBK, C6H12O).

10.1.9 Hydrochloric acid (HCl). guaranteed reagent.

10.2 Preparation of reagents

10.3 Standard

Lead nitrate [Pb(NO3)2, CAS number. 10099-74-8]. purity >99.99%, or lead standard

solution certified by the state and granted with a reference material certificate.

10.4 Preparation of standard solution

10.4.1 Lead standard stock solution (1 000 mg/L). Accurately weigh 1.598 5 g (accurate

to 0.000 1 g) of lead nitrate; use a small amount of nitric acid solution (1+9) to dissolve

it; transfer it to a 1 000 mL volumetric flask; add water to the mark; mix well.

10.4.2 Lead standard working solution (10.0 mg/L). Accurately draw 1.00 mL of lead

standard stock solution (1 000 mg/L) into a 100 mL volumetric flask; add nitric acid

solution (5+95) to the mark; mix well.

11.1 Atomic absorption spectrometer. equipped with flame atomizer and accompanied

by lead hollow cathode lamp.

11.2 Analytical balance. The sensitivity is 0.1 mg and 1 mg, respectively.

11.3 Adjustable electric furnace and adjustable electric hot plate.

12.1 Sample preparation

Same as 5.1.

12.2 Sample pretreatment

Same as 5.2.1.

12.3 Determination

12.3.1 Apparatus reference conditions

See Appendix D for apparatus reference conditions.

12.3.2 Preparation of standard curve

Respectively draw 0 mL, 0.25 mL, 0.50 mL, 1.00 mL, 1.50 mL and 2.00 mL of lead

standard working solution (equivalent to 0 µg, 2.50 µg, 5.00 µg, 10.0 µg, 15.0 µg and

20.0 µg of lead) into 125 mL separatory funnels; add additional water to 60 mL. Add 2

mL of ammonium citrate solution (250 g/L), 3 ~ 5 drops of bromothymol blue aqueous

solution (1 g/L); use ammonia solution (1+1) to adjust the pH until the solution changes

from yellow to blue; add 10 mL of ammonium sulfate solution (300 g/L) and 10 mL of

DDTC solution (50 g/L); shake well. Leave it for about 5 minutes; add 10 mL of MIBK;

shake vigorously for extraction for 1 min; let it stand for layering; discard the water

layer; put the MIBK layer into a 10 mL graduated tube with a stopper to obtain a

standard series of solutions.