Testing of dairy products/food additives

3.2.13 Cation exchange cell phase extraction column r mixed type cation exchange solid-phase extraction column, with a substrate of benzene sulfonated polystyrene divinylbenzene polymer, a filler mass of 60 mg, a volume of 3 mL, or equivalent. Activate with 3 mL of methanol and 5 mL of water before use. 3.2.14 Qualitative filter paper. 3.2.15: Sea sand: chemically pure, with a particle size of 0.65 nm~0.85 nm and a silicon dioxide (SiO:) content of 99%. 3.2.16 Microporous filter membrane: 0.2 um, organic phase. 3.2.17 Nitrogen: Purity greater than or equal to 99.999%. 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: sensitivity of 0.000 1g and 0.01 g. 3.3.3 Centrifuge: speed not less than 40o0 r/min. 3.3.4 Ultrasonic water bath. 3.3.5 Solid phase extraction device. 3.3.6 Nitrogen drying instrument. 3.3.7 Vortex Mixer. 3.3.8 Plastic centrifuge tube with stopper: 50 mL. 3.3.9 Mortar. 3.4 Sample Processing 3.4.1 Extraction 3.4.1.1 Weigh 2. g of liquid milk, milk powder, yogurt, ice cream, and lactose to the nearest 0.01 g. Place the sample in a 50 mL stoppered plastic centrifuge tube, add 15 mL of trichloroacetic acid solution (3.2.8) and 5 mL of acetonitrile, extract with ultrasound for 10 minutes, shake for 10 minutes, and centrifuge at a rate of not less than 4000 r/min. After filtering the supernatant through filter paper moistened with trichloroacetic acid solution, bring it to a constant volume of 25 mL with trichloroacetic acid solution, transfer 5 mL of the filtrate, add 5 mL of water, and mix to make the purified solution. 3.4.1.2 Weigh 2 g (accurate to 0.01 g) of cheese, cream, and chocolate samples into a mortar, add an appropriate amount of sea sand (4 to 6 times the mass of the sample), grind them into dry powder, transfer them to a 50 mL stoppered plastic centrifuge tube, clean the mortar with 15 mL of trichloroacetic acid solution (3.2.8) in fractions, transfer the cleaning solution into the centrifuge tube, and then add 5 mL of acetonitrile to the centrifuge tube, The remaining operations are the same as in section 3.4.1.1, "Ultrasonic extraction for 10 minutes,... add 5 mL of water and mix well before making the purified solution. Note: If the fat content in the sample crystal is high, it can be removed by liquid-liquid distribution of n-hexane saturated with trichloroacetic acid solution and then purified with an SPE column. 3.4.2 Purification Transfer the liquid to be purified in 3.4.1 to a solid-phase extraction column (3.2.13). Wash with 3 mL of water and 3 mL of methanol in sequence, draw to near dryness, and elute with 6 mL of ammoniated methanol solution (3.2.9). The flow rate of the entire solid-phase extraction process shall not exceed 1 mL/min. The eluent was dried with nitrogen gas at 50 ℃, and the residue (equivalent to 0.4 g of sample) was diluted with l mL of mobile phase. Vortex mixing was performed for 1 minute, and then filtered through a microporous filter membrane (3.2.16) for HPLC determination. 3.5 High performance liquid chromatography determination 3.5.1 HPLC reference condition a) Chromatographic column; C. Column, 250 mm × 4.6 mm [inner diameter (i.d.)], 5 um, or equivalent. Cs column, 250 tnm × 4.6 nm [inner diameter (i.d.) J, 5 um, or equivalent. b) mobile phase: C. column, ion pair reagent buffer (3.2.10) - acetonitrile (85+15, volume ratio), mix well. Ce column, ion pair reagent buffer (3.2.10) - acetonitrile (90+10, volume ratio), mix well. c flow rate: 1.0 tnL/min, d column temperature: 40 ℃. e) wavelength: 240 nm

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