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5.
2.
1.
1 Scope of application
It is suitable for the determination of 9 penicillin residues in cattle, sheep, pigs and chicken by liquid chromatography-tandem mass spectrometry
.
Detection limit of the method: Nafcillin is 0.
5.
2.
1.
2 Principle of the method
9 kinds of penicillin residues in the sample, extracted with 0.
15mol/L sodium dihydrogen phosphate (pH8.
5) buffer solution, centrifuged, the supernatant was purified with a solid phase extraction column, determined by liquid chromatography-tandem mass spectrometry, external standard Method quantitative
.
5.
2.
1.
3 Reagents and materials
Both methanol and acetonitrile are chromatographically pure; sodium dihydrogen phosphate (NaH 2 PO 4 ), sodium hydroxide , and acetic acid are all top grade pure; acetonitrile + water (1+1, v/v): measure 50 mL acetonitrile and 50 mL water Mix; Sodium hydroxide solution: 5mol/L
.
Weigh 20g of sodium hydroxide, dissolve in water, and dilute to 100mL; sodium dihydrogen phosphate buffer solution: 0.
Amoxicillin, ampicillin, piperacillin, penicillin G, penicillin V, oxacillin, cloxacillin, nafcillin, and dicloxacillin 9 standard penicillin standards: purity ≥99%
.
Nine penicillin standard stock solutions: accurately weigh an appropriate amount of each standard substance, and prepare a standard stock solution with a concentration of 1.
0 mg/mL with water
.
The stock solution is stored in a -18°C freezer
9 kinds of penicillin standard working solutions: draw an appropriate amount of each penicillin standard stock solution as needed, and dilute with the blank sample extract to form a matrix mixed standard working solution of appropriate concentration
.
BUNDELUT C18 solid phase extraction column or equivalent: 500mg, 6mL
.
Before use, pretreated with 5mL methanol, 5mL water and 10mL sodium dihydrogen phosphate buffer solution to keep the column moist
5.
2.
1.
4 Instruments and equipment
Liquid chromatography-tandem quadrupole mass spectrometer, equipped with electrospray ion source; analytical balance: sensitivity 0.
1mg and 0.
01g; oscillator; solid phase extraction vacuum device; reservoir: 50mL; micro syringe: 25μL, 100μL ; Scaled sample tube: 5mL, with an accuracy of 0.
1mL; centrifuge: with a 50mL centrifuge tube with stopper; pH meter: measurement accuracy of 0.
02pH unit
.
5.
2.
1.
5 Sample pretreatment
Weigh 3g sample (accurate to 0.
01g) into a 50mL centrifuge tube, add 25mL sodium dihydrogen phosphate buffer solution, shake on a shaker for 10 minutes, then centrifuge at 4000r/min for 10 minutes, and move the upper extract to the bottom In the reservoir connected to the BUNDELUT C 18 solid phase extraction column, pass through the solid phase extraction column at a flow rate of 3 mL/min, wash the column with 2 mL of water, and discard all the effluent
.
Elute with 3mL of acetonitrile+water, collect the eluate in a graduated sample tube, dilute to 3mL with acetonitrile+water, shake well, pass through a 0.