Analysis of pesticide residues in eggs by direct sample introduction/gas chromatography/tandem mass spectrometry

Direct sample introduction (DSI) or "dirty sample injection" is a rapid, ru gged, and inexpensive approach to large volume injection in gas chromatogra phy (GC) for semivolatile analytes such as pesticides. DSI of complex sampl es such as eggs requires a very selective, detection technique, such as tan dem mass spectrometry (MS-MS), to determine the analytes among the many sem ivolatile matrix components that also appear. In DSI, the nonvolatile matri x components that normally would contaminate the GC system in traditional i njection methods remain in a disposable microvial, which is removed after e very injection. For example, 3 mug of nonvolatile residue typically remaine d in the microvial after an injection of egg extract using the DSI method. This analytical procedure involves the following: W weighing 10 g of egg in a centrifuge tube and adding 2 g of NaCl and 19.3 mL of acetonitrile (MeCN ); (ii) blending for 1 min using a probe blender; (iii) centrifuging for 10 min; and (iv) analyzing 10 muL (5 mg of egg equivalent) of the extract usi ng DSI/GC/MS-MS. No sample cleanup or solvent evaporation steps were requir ed to achieve quantitative and confirmatory results with < 10 ng/g detectio n limits for 25 of 43 tested pesticides from several chemical classes. The remaining pesticides gave higher detection limits due to poor fragmentation characteristics in electron impact ionization and/or degradation. Analysis of eggs incurred with chlorpyrifos-methyl showed a similar trend in the re sults as a more traditional approach.