GB/T 5009.74-2003 English PDF (GBT5009.74-2003)

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GB/T 5009.74-2003: Method for limit test of heavy metals in food additives
GB/T 5009.74-2003
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 67.040
C 53
Replaces GB/T 8451-1987
Method for Limit Test of Heavy Metals in Food Additives
ISSUED ON: AUGUST 11, 2003
IMPLEMENTED ON: JANUARY 1, 2004
Issued by: Ministry of Health;
Standardization Administration of the People’s Republic of China.
Replaced by GB 5009.74-2014
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Principle ... 4
3 Reagents ... 4
4 Apparatus ... 5
5 Test Sample Treatment ... 5
6 Determination ... 6
Method for Limit Test of Heavy Metals in Food Additives
1 Scope
This standard specifies the method for limit test of heavy metals in food additives.
This standard is applicable to the limit test of heavy metals in food additives.
2 Principle
Under the condition of weak acid (pH 3~4), heavy metal ion in the test sample will act
with hydrogen sulfide to generate a substance in brownish black; compare with the lead
standard solution that is treated in the same way; conduct the limit-amount test.
3 Reagents
3.1 Nitric acid.
3.2 Sulfuric acid.
3.3 Hydrochloric acid.
3.3.1 6 mol/L hydrochloric acid: measure 50mL of hydrochloric acid; dilute it with
water to 100 mL.
3.3.2 1 mol/L hydrochloric acid: measure 8.3mL of hydrochloric acid; dilute it with
water to 100 mL.
3.4 Ammonia water
3.4.1 6 mol/L ammonia water: measure 40mL of ammonia water; dilute it with water
to 100 mL.
3.4.2 1 mol/L hydrochloric acid: measure 6.7mL of ammonia water; dilute it with
water to 100 mL.
3.5 Acetate buffer solution (pH3.5): weigh 25.0g of ammonium acetate; dissolve it in
25mL water; add 45mL of 6 mol/L hydrochloric acid; adjust the pH value to 3.5 by
using diluted hydrochloric acid or weak aqua ammonia; dilute it with water to 100 mL.
3.6 Phenolphthalein indicating liquid: 1% ethanol solution.
3.7 Saturated hydrogen sulfide water: inject hydrogen sulfide gas into water free of
and sulfuric acid for reagent blank test according to the above method.
5.2.2 Dry digestion: this method is applicable to the test sample to which wet
digestion is not applicable.
Weigh 5.0g of test sample; place it in the crucible; and add adequate amount of sulfuric
acid to soak the test sample. After charring on soft fire, add 2mL of nitric acid and 5
drops of sulfuric acid; carefully heat until white fume is exhausted. Transfer to the high
temperature stove; complete the ashing at 550℃; cool and take it out; add 2mL of 6
mol/L hydrochloric acid to moisten the residue; and gradually evaporate to dryness on
the water bath. Use 1 drop of concentrated hydrochloric acid to moisten the residue;
add 10mL water; heat on the water bath again for another 2min; transfer the solution
into a 50mL volumetric flask; filter where necessary; wash the crucible and filter by
using a small amount of water; also transfer the washing filtrate into the volumetric
flask; and mix uniformly. Each 10mL of this solution is equivalent to 1.0g of test sample.
Taken another crucible while test sample ashing to carry out reagent blank test
according to above method.
6 Determination
6.1 A-tube: pipette a certain amount of lead standard solution containing lead (at least
10μg of lead) equivalent to the designated heavy metal limit; transfer it to a 50mL
Nessler tube (if the test sample is subject to treatment, pipette the reagent blank solution
equivalent to the sample solution); add water to 25mL; mix uniformly; add 1 drop of
phenolphthalein indicating liquid; adjust pH value by using 6 mol/L diluted
hydrochloric acid or 1 mol/L weak aqua ammonia to be neutral (phenolphthalein red
just disappears); add 5mL of acetate buffer solution (pH 3.5); and mix uniformly for
use.
6.2 B-tube: take a Nessler tube matching with A-tube; add 10mL~20mL (or adequate
amount) of sample solution; add water to 25mL; mix uniformly; add 1 drop of 1%
phenolphthalein indicating liquid; adjust pH value by using 6 mol/L diluted
hydrochloric acid or 1 mol/L weak aqua ammonia to be neutral (phenolphthalein red
just disappears); add 5mL of acetate buffer solution (pH 3.5); and mix uniformly for
use.
6.3 C-tube: take a Nessler tube matching with A- and B-tubes; add sample solution
equivalent and identical to that in B-tube; add lead standard solution equivalent to that
in A-tube; add water to 25mL; mix uniformly; add 1 drop of 1% phenolphthalein
indicating liquid; adjust pH value by using diluted hydrochloric acid or weak aqua
ammonia (6 mol/L or 1 mol/L) to be neutral (phenolphthalein red just disappears); add
5mL of acetate buffer solution (pH 3.5); and mix uniformly for use.
6.4 Add 10mL of freshly-prepared saturated hydrogen sulfide liquid into each tube;
add water to 50mL mark; mix uniformly; and place in the dark for 5min. Observe under