GB/T 22388-2008Determination of melamine in raw milk and dairy products (English PDF)

3.3 Instruments and equipment

3.3.1 High performance liquid chromatography (HPLC) instrument. equipped with UV Detector or diode array detector.

3.3.2 Analytical balance. resolution is 0.0001 g and

0.01 g.

3.5.1 HPLC reference conditions

3.5.2 Drawing of standard curve Use mobile phase to dilute the melamine standard stock solution grade by grade to obtain the standard working solutions with concentrations of 0.8, 2, 20, 40, 80 µg/mL. Test the concentration from low to high. With peak area- concentration, obtain the standard curve regression equation. See Figure A.1 in Annex A for HPLC chromatogram of matrix matching melamine sample.

3.7 Method limit of quantification The limit of quantification of this Method is 2 mg/kg.

3.8 Rate of recovery In the concentration range of 2mg/kg ~ 10mg/kg, the recovery rate is between 80% ~ 110%, and the relative standard deviation is less than 10%.

3.9 Allowable difference The absolute difference between two independent determinations obtained under repeatability conditions must not exceed 10% of the arithmetic mean.

4 Method Two -- Liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS)

4.1 Principle Extract sample with trichloroacetic acid solution. After purification by cation exchange solid phase extraction column, determine by liquid chromatography- mass spectrometry/mass spectrometry; quantify by external standard method.

4.2 Reagents and materials Unless otherwise specified, all reagents are analytically pure, and water is grade one according to GB/T 6682.

4.3 Instruments and equipment

4.3.1 Liquid chromatography-mass spectrometry/mass spectrometry (LC- MS/MS) instrument. equipped with electron spray ionization (ESI).

4.3.2 Others same with 3.3.

4.4.2 Purification Transfer the liquid to be purified in

4.4.1 to the solid phase extraction column (3.2.13). Wash sequentially with 3 mL of water and 3 mL of methanol. After pumping to near dryness, elute with 6 mL of ammoniated methanol solution (3.2.9).

4.5.1 LC reference conditions

4.5.3 Drawing of standard curve Take blank sample and process it according to 4.4.Use the sample solution obtained to dilute the melamine standard stock solution (3.2.12) grade by grade to obtain the standard working solutions with concentrations of 0.01, 0.05, 0.1, 0.2, 0.5 µg/mL.

4.5.4 Quantitative determination The melamine response in the sample to be tested shall be within the linear range of the standard curve. When it exceeds the linear range, the injection analysis shall be performed after dilution.

4.6 Blank test Except that the sample is not weighed, it is performed according to the above measurement conditions and steps.

4.7 Method limit of quantification The limit of quantification of this Method is

0.01 mg/kg.

4.8 Rate of recovery In the concentration range of 0.01mg/kg ~ 0.5mg/kg, the recovery rate is between 80% ~ 110%, and the relative standard deviation is less than 10%.

4.9 Allowable difference The absolute difference between two independent determinations obtained under repeatability conditions must not exceed 15% of the arithmetic mean.

5.3 Instruments and equipment

5.3.1 Gas chromatography-mass spectrometry (GC-MS) instrument. equipped with electron impact ionization (EI).

5.3.2 Gas chromatography-mass spectrometry/mass spectrometry (GC- MS/MS) instrument. equipped with electron impact ionization (EI).

5.3.3 Electronic incubator.

5.3.4 Same with 3.3.

5.4.2.1 Milk powder, cheese, butter, chocolate and toffee, etc. Weigh

0.5 g of (to the nearest of

0.01

g) sample. Add into 5 mL of methanol aqueous solution (3.2.7). After vortex mixing for 2 min, perform ultrasonic extraction for 15min ~ 20min. Centrifuge at no less than 4000 r/min for 10min.

5.5.1 Instrument reference conditions

5.6 Blank test Except that the sample is not weighed, it is performed according to the above measurement conditions and steps.

5.7 Method limit of quantification In this method, the limit of quantification of the GC-MS method is

0.05 mg/kg, and the limit of quantitation of the gas chromatography-mass spectrometry/mass spectrometry (GC-MS/MS) is

0.005 mg/kg.

5.8 Rate of recovery GC-MS method. in the concentration range of 0.05mg/kg ~ 2mg/kg, the recovery rate is between 70% ~ 110%, and the relative standard deviation is less than 10%.