Determination Of Multiple Pesticides Residue In Milk And Milk Powder By LC-MS/MS

With the increasing consumption of milk products, analysts are paying increasing attention to the study of techniques for analysis of pesticide residues in milk and milk powder products. However, according to the study of the current status, milk and milk powder in the presence of pesticide residue analysis was obviously inadequate. Most studies focused on single residue or selective multi-residue residues, lacked of multi-pesticide residues detection methods and new technologies. Establishing a rapid and efficient multi-pesticide residues determination method for milk products has become urgent problem to solve.In this study, solid phase extraction (SPE) was chosen for sample processing, and LC-MS/MS was chosen as detecting technique, establishing a determination method for 285 pesticides (including organophosphate, organochlorine, pyrethroid category, and so on) in milk and milk powder. Experimental results and conclusions were as follows:(1) Determination method for pesticides residues in milk: Adding 20 mL acetonitrile, 4 g of magnesium sulfate and 1 g NaCl into 10 mL milk, shaking, and then separating by centrifuge, collecting the supernatant, extraction processing was repeated two times. Then cleaned up by a C18 solid phase extraction cartridge to remove the lipophilic compounds after the supernatant concentrated with a rotary evaporator. Eluate was collected, and concentrated at 45℃under dry nitrogen. The 1 mL mixture of acetonitrile and water (3:2,V/V) was added to the sample and mixed thoroughly for 30 s. The sample solution was filterd by millipore filters before liquid chromatography-tandem mass spectrometry (ESI source) determination. The the average spiking recoveries in milk martrix for 281 kinds pesticides at low level (0.05μg/L ~ 1.12 mg/L ) there were 258 kinds in the range 60.42 % ~ 119.57 %, and 246 kinds with RSDs < 20 %; the average spiking recoveries at high level (0.2μg/L ~ 4.48 mg/L) there were 267 kinds in range 60.32 % ~ 118.52 %, and 263 kinds with RSDs < 20 %.(2) Determination method for pesticides residues in milk: Adding 20 mL acetonitrile, 4 g of magnesium sulfate into 3 g milk powder, shaking, and then separating by centrifuge, collecting the supernatant, extraction processing was repeated two times. Then cleaned up by a C18 solid phase extraction cartridge to remove the lipophilic compounds after the supernatant concentrated with a rotary evaporator. Eluate was collected, and concentrated at 45℃under dry nitrogen. The 1 mL mixture of acetonitrile and water (3:2,V/V) was added to the sample and mixed thoroughly for 30 s. The sample solution was filterd by millipore filters before liquid chromatography-tandem mass spectrometry (ESI source) determination. The the average spiking recoveries in milk powder martrix for 279 kinds pesticides and related chemicals at low-level (0.17μg/kg ~ 3.73 mg/kg ) there were 236 kinds in the range 60.27 % ~ 119.55 %,and 244 kinds with RSDs < 20 %, the average spiking recoveries at high level (0.67μg/kg ~ 14.93 mg/kg ) ther were 252 kinds in the range 60.11 % ~ 115.13 % ,and 260 kinds with RSDs < 20 %.(3) The results also shown that the method established by this study, 275 kinds of pesticides are suitable for the determination of milk and milk powder matrix, 6 other kinds of pesticide are only suitable for the determination of milk matrix , and 4 kinds of pesticides are only suitable for species measured in the milk powder matrix. The detection limits of milk and milk powder martrix were during 0.05μg / L ~ 0.56 mg / L and 0.08μg/kg ~ 1.87 mg/kg.The results demonstrated that this method is simple, rapid and character-ized with acceptable sensitivity and accuracy to meet the requirements of the multiple pesticide residue analysis.