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8.
2.
2.
5 Sample preparation
(1) Sample preparation
Take 500g of sample, stir and mix well, put it into a clean container as a sample, seal it, and mark it with a mark
.
If the prepared sample is not measured immediately, store the test sample at 4°C
(2) Sample weighing
a.
Milk sample Weigh 10g (accurate to 0.
01g) milk sample and place it in a 50mL polypropylene centrifuge tube with a stopper
.
b.
Milk powder sample Weigh 1g sample (accurate to 0.
01g), place it in a 50mL polypropylene centrifuge tube with stopper, then add 8 times the mass of water to dissolve and mix
.
(3) Sample extraction
Add 1.
0mL ammonia and mix well
.
Was added 10mL 95% ethanol was added 10mL after mixing with ethyl acetate , shaken for 1min, then was added 10mL of petroleum ether , shaking the same 1min, to / centrifugation min 4000r 5min, draw the upper extract containing 15g through anhydrous sodium sulfate to Filter the glass column into a 50 mL polypropylene centrifuge tube with a stopper
Add 5 mL of acetonitrile and keep it in a 60°C water bath for 3 minutes to melt the fat
.
Vortex for 1 min, centrifuge at 4000 r/min at -5°C for 7 min, draw the supernatant into a 15 mL stoppered polypropylene centrifuge tube, add 5 mL of acetonitrile to the precipitate and repeat the extraction once, and combine the supernatants
(4) Saponification
Add 4mL n-hexane, 1mL sodium hydroxide solution and 0.
5mL magnesium chloride solution to the acetonitrile extract in sequence , mix quickly on a liquid mixer for 10s, keep in a 60℃ water bath for 15min, and at -5℃ at 4000r/min Centrifuge for 5 min, and transfer the supernatant to a 15 mL centrifuge tube
.
Add 4 mL of n-hexane to the precipitate, mix well, heat in a water bath at 60°C for 15 minutes, centrifuge at 4000r/min at -5°C for 5 minutes, and combine the supernatants
(4) Saponification
Add 4mL n-hexane, 1mL sodium hydroxide solution and 0.
5mL magnesium chloride solution to the acetonitrile extract in sequence, mix quickly on a liquid mixer for 10s, keep in a 60℃ water bath for 15min, and at -5℃ at 4000r/min Centrifuge for 5 min, and transfer the supernatant to a 15 mL centrifuge tube
.
Add 4 mL of n-hexane to the precipitate, mix well, heat in a water bath at 60°C for 15 minutes, centrifuge at -5°C at 4000 r/min for 5 minutes, and combine the supernatants
(5) Purification
The above sample solution was transferred to the cyanopropyl solid phase extraction column, the glass test tube was rinsed twice with 2 mL of n-hexane, and the washing liquid was also transferred to the solid phase extraction column
.
After the sample solution flows out, wash the solid phase extraction column with 5 mL n-hexane and 6 mL ethyl acetate + n-hexane solution (1+19, v/v) in sequence.