GB 31604.25-2016National standard for food safety - Determination of chromium migration quantity in food contact materials and products (English PDF)

3.1 Reagents

3.1.1 Nitric acid (HNO3).

3.1.2 Ammonium dihydrogen phosphate (NH4H2PO4).

4.1 Graphite furnace atomic absorption spectrometer. equipped with a

graphite furnace atomizer and a chrome hollow cathode lamp.

4.2 Analytical balance. with a sensibility of 0.1mg.

5.1 Pretreatment of sample

CARRY out the migration test based on the intended use and conditions of use

of the samples to be tested, and in accordance with the migration test methods

and test conditions specified in GB 5009.156 and GB 31604.1. MIX the soaking

solution fully and evenly. TAKE some of the soaking solution for analysis. If the

soaking solution is neutral or basic, ADD appropriate amount of nitric acid so

that the concentration of nitric acid in the test solution is about 5% (volume

fraction). In the meantime, CARRY out the sample blank test.

5.2 Determination

5.2.1 Instrument reference conditions

SEE Table A.1 for the instrument reference conditions.

5.2.2 Preparation of standard curve

TAKE 10µL of chromium standard series solution and 5µL of ammonium

dihydrogen phosphate solution (20g/L), respectively (optimal injection volume

can be determined according to the instruments in use). In the meantime,

INJECT into a graphite furnace for the determination of absorbance. PREPARE

the standard curve by taking the concentrations of standard series as x-

coordinates and the corresponding absorbance as y-coordinates.

5.2.3 Determination of sample solution

TAKE 10µL of blank solution and sample soaking solution as well as 5µL of

ammonium dihydrogen phosphate solution (20g/L), respectively (optimal

injection volume can be determined according to the instruments in use). In the

meantime, INJECT into a graphite furnace. DETERMINE its absorbance after

atomization. COMPARE with the standard series for quantitation.

12.1 Pretreatment of sample

Same as Subclause 5.1.

12.2 Determination

12.2.1 Preparation of standard curve

DRAW 0mL, 0.250mL, 0.500mL, 1.00mL, 1.50mL, 2.00mL, 2.50mL and 3.00mL

of chromium standard solution. TRANSFER to a 50.0mL volumetric flask,

respectively. ADD the corresponding food simulant to the scale. TRANSFER

standard series solution to a 100mL conical flask. ADD two glass beads and

several drops of sulfuric acid solution (2.5mol/L) and potassium permanganate

solution (3g/L). MIX evenly. BOIL to about 30mL [after the reddish color

disappears, ADD potassium permanganate solution (3g/L) again until the

reddish color appears]. After cooling, ADD 25.0mL of urea solution (200g/L).

MIX evenly. Dropwise ADD sodium nitrite solution (100g/L) until the reddish

color disappears. ADD saturated sodium hydroxide solution until the mixture is

basic (pH = 9). LET it stand for 2h. FILTER afterwards. ADD water to filtrate to

100mL. MIX evenly. TAKE 20.0mL of this solution. ADD it to a 25mL colorimetric

tube. ADD 1mL of sulfuric acid solution (2.5mol/L) and 1mL of sodium

pyrophosphate solution (50g/L). MIX evenly. ADD 2mL of diphenylcarbazide

solution. ADD water to 25.0mL. MIX evenly. LET it stand for 5min. DETERMINE

the absorbance at 540nm. PREPARE the standard curve by taking the

absorbance as y-coordinates and the chromium mass as x-coordinates.

12.2.2 Determination of sample solution

TAKE 50.0mL of sample soaking solution. ADD it to a 100mL conical flask. ADD

two glass beads and several drops of sulfuric acid solution (2.5mol/L) and

potassium permanganate solution (3g/L). MIX evenly. BOIL to about 30mL [after

the reddish color disappears, ADD potassium permanganate solution (3g/L)

again until the reddish color appears]. After cooling, ADD 25.0mL of urea

solution (200g/L). MIX evenly. Dropwise ADD sodium nitrite solution (100g/L)

until the reddish color disappears. ADD saturated sodium hydroxide solution

until the mixture is basic (pH = 9). LET it stand for 2h. FILTER afterwards. ADD

water to filtrate to 100mL. MIX evenly. TAKE 20.0mL of this solution. ADD it to

a 25mL colorimetric tube. ADD 1mL of sulfuric acid solution (2.5mol/L) and 1mL

of sodium pyrophosphate solution (50g/L). MIX evenly. ADD 2mL of

diphenylcarbazide solution. ADD water to 25.0mL. MIX evenly. LET it stand for

5min. DETERMINE the absorbance at 540nm. In the meantime, CARRY out

the sample blank test.

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