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GB 5009.282-2020: National food safety standard - Determination of 1-methylimidazole, 2-methylimidazole and 4-methylimidazole in foods
GB 5009.282-2020
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National food safety standard - Determination of 1-
methylimidazole, 2-methylimidazole and 4-methylimidazole
in food
ISSUED ON. SEPTEMBER 11, 2020
IMPLEMENTED ON. MARCH 11, 2021
Issued by. National Health Commission of PRC;
State Administration for Market Regulation.
Table of Contents
1 Scope... 3
2 Principles... 3
3 Reagents and materials... 3
4 Instruments and equipment... 6
5 Analysis steps... 6
6 Presentation of analysis results... 10
7 Precision... 11
8 Others... 11
Appendix A Reference mass spectrometry conditions... 12
Appendix B Chromatogram of standards... 13
National food safety standard - Determination of 1-
methylimidazole, 2-methylimidazole and 4-methylimidazole
in food
1 Scope
This standard specifies the method for the determination of 1-methylimidazole, 2-
methylimidazole, and 4-methylimidazole in food by liquid chromatography-tandem
mass spectrometry.
This standard applies to the determination of the content of 1-methylimidazole, 2-
methylimidazole, and 4-methylimidazole in condensed milk, frozen drinks, jams, soy
products, cocoa and chocolate products, candy, wheat flour products, biscuits, fillings
and surface slurries, meat products, flavored syrups, condiments (soy sauce, vinegar,
sauce and sauce products, cooking wine, compound seasoning), beverages, wine, jelly,
and puffed food.
2 Principles
After adding the isotope internal standard to the sample, carry out the extraction with
water or acid water, perform the purification and concentration by a solid-phase
extraction column, determine by a liquid chromatography-tandem mass spectrometer,
and use the isotope internal standard method for quantification.
3 Reagents and materials
Unless otherwise specified, the reagents used in this method are all analytical reagents,
and the water is the grade I water specified in GB/T 6682.
3.1 Reagents
3.1.1 Acetonitrile (CH3CN). chromatographically pure.
3.1.2 Methanol (CH3OH). chromatographically pure.
3.1.3 Formic acid (HCOOH). chromatographically pure.
3.1.4 Ammonia water (NH4OH). The concentration shall be 25%~28%.
3.1.5 N-hexane (CH3(CH2)4CH3). chromatographically pure.
3.1.6 Ammonium acetate (CH3COONH4). chromatographically pure.
3.1.7 Sodium chloride (NaCl).
3.2 Reagent preparation
3.2.1 2% formic acid aqueous solution. Measure out 20 mL of formic acid, add it to 980
mL of water, and mix well.
3.2.2 Ammonia methanol solution. Measure out 50 mL of ammonia water, add it to 950
mL of methanol, and mix well.
3.2.3 Ammonium acetate solution (5 mmol/L). Weigh 0.39 g of ammonium acetate,
dissolve it in 1000 mL of water, and mix well.
3.2.4 Acetonitrile-ammonium acetate solution (9+1). Mix acetonitrile and ammonium
acetate solution (5 mmol/L) uniformly in a volume ratio of 9.1.
3.3 Standards
3.3.1 1-methylimidazole standard (C4H6N2, CAS number. 616-47-7). purity ≥98%, or
a standard substance certified by the country and granted a standard substance
certificate.
3.3.2 2-methylimidazole standard (C4H6N2, CAS number. 693-98-1). purity ≥98%, or
a standard substance certified by the country and granted a standard substance
certificate.
3.3.3 4-methylimidazole standard (C4H6N2, CAS number. 822-36-6). purity ≥98%, or
a standard substance certified by the country and granted a standard substance
certificate.
3.3.4 Isotope internal standard 1-methylimidazole-D6 (C4H6N2, CAS number. 285978-
27-0). purity ≥98%.
3.3.5 Isotopic internal standard 2-methylimidazole-D6 (C4H6N2, CAS number.
1173022-19-9). purity ≥98%.
3.3.6 Isotope internal standard 4-methylimidazole-D6 (C4H6N2, CAS number. 1219804-
79-1). purity ≥98%.
3.4 Standard solution preparation
3.4.1 Standard stock solution (1 mg/mL). Accurately weigh 25 mg of 1-
methylimidazole standard (the weight shall be accurate to 0.01 mg), add 1 mL of water
to dissolve it, and transfer it with acetonitrile to a 25 mL brown volumetric flask; make
up to the mark and shake well. Accurately weigh 25 mg of 2-methylimidazole standard
and 4-methylimidazole standard respectively (the weight shall be accurate to 0.01 mg),
dissolve them with acetonitrile, and transfer to 25mL brown volumetric flasks;
respectively dilute to the mark and shake well. Keep them sealed at -20 ℃ and away
from light, then they are valid for 6 months.
3.4.2 Mixed standard working solution (2.0 μg/mL). Pipette 100 μL of each of the above
standard stock solutions into the same 50 mL brown volumetric flask, add acetonitrile
to dilute to the mark, and shake well; then, the mixed standard solution of 2.0 μg/mL is
obtained. Keep this solution sealed at 4 ℃ and away from light, then it is valid for 3
months.
3.4.3 Isotope internal standard stock solution (1 mg/mL). Accurately weigh 10 mg of
1-methylimidazole-D6, 2-methylimidazole-D6, and 4-methylimidazole-D6 respectively
(the weight shall be accurate to 1 mg), dissolve them with acetonitrile, and transfer to
10 mL brown volumetric flasks; dilute to the mark and shake well. Keep them sealed at
-20 ℃ and away from light, then they are valid for 6 months.
3.4.4 Isotope internal standard mixed working solution (1.0 μg/mL). Pipette 100 μL of
each of the above isotope internal standard stock solutions into the same 100 mL brown
volumetric flask, dilute to the mark with acetonitrile, and shake well; then, the isotopic
internal standard mixed working solution of 1.0 μg/mL is obtained. Keep this solution
sealed at 4 ℃ and away from light, then it is valid for 3 months.
3.4.5 Standard series solutions. Pipette 25 μL, 75 μL, 150 μL, 300 μL, 600 μL, and
1000 μL of mixed standard working solutions into 5 mL brown volumetric flasks,
respectively, add 250 μL of isotope internal standard mixed working solution, and use
acetonitrile- ammonium acetate solution (9+1) to dilute the mixed solution to the scale;
then, the mixed standard series solution of 1-methylimidazole, 2-methylimidazole and
4-methylimidazole are prepared, and the mass concentration is 10 ng/mL, 30 ng/mL,
60 ng/mL, 120 ng/mL, 240 ng/mL, 400 ng/mL respectively. In the actual sample
determination, the added amount and dilution multiple of the isotope internal standard
mixed working solution can be adjusted according to the sample concentration.
3.5 Materials
3.5.1 Mixed cation exchange solid phase extraction column. N-vinylpyrrolidone-
divinylbenzene copolymer matrix-sulfonic acid group, 150 mg, 6 mL, or equivalent.
Before use, activate it with 5 mL methanol first, and then rinse it with 5 mL water to
balance.
3.5.2 Homogeneous particle. It shall be suitable for 50 mL centrifuge tubes.
3.5.3 Organic filter membrane. The pore size shall be 0.22 μm.
volume to 20 mL, and shake well; put it in a centrifuge tube, and centrifuge at 10,000
r/min for 5 min; the supernatant is to be purified later.
5.1.2.2 Semi-fluid samples (such as jam, oyster sauce, flavored syrup, frozen drinks)
and gum-based candy, tapioca balls
Weigh 2 g of uniformly mixed sample (the weight shall be accurate to 0.001 g), and put
it in a 50 mL centrifuge tube; add 100 μL of 1.0 μg/mL isotope internal standard mixed
working solution, and mix well; add 20 mL of water accurately, vortex for 1 min, and
heat it in a water bath at 70 °C for 10 min. After it cools to room temperature, perform
the ultrasonic extraction for 20 min, and centrifuge at the speed of 10,000 r/min and the
temperature of 4 ℃ for 5 min; the supernatan...