Options in Veterinary Residue Analysis using LC—MS

A detail discussion on LC—MS techniques would be outside the scope of the present chapter therefore we focus on the possibilities and limitations of the current LC—MS methods applied to veterinary residue 

Non a-priorf Screening idenlificalion of unknown or selected compounds 

In residue analysis, sample preparation is often the bottleneck [15]. Several reviews devoted to this topic have been published in recent years [16-18]. 

Although the high selectivity of the MS systems can overcome problems related to the presence of interfering compounds extracted from such complex matrices, nevertheless, qualitative and quantitative analysis are severely affected by the unwelcome matrix effect frequently occurring when using electrospray (ESI)-MS sources. Therefore, the complexity of the food matrices and the legal residue limits (on the order of ng g ), generally impose adequate sample preparation before LC—MS determination. 

Typical sample preparation steps include homogenization, extraction (liquid—liquid extraction, LLE, or instrumental based techniques), cleanup (usually by solid-phase extraction, SPE), and concentration of extracts. Sometimes, derivatization has to be incorporated into sample preparation (e.g., release of bormd residues or deconjugation). For quantitative analysis, the preparation of adequate calibration standards also may be a key aspect in some cases, matrix-matched standards or the standard additions method may be necessary, as well as the use of suitable internal standards (e.g., isotopically labeled compormds) [19]. Matrix-matched calibration is now preferred, as it is the best compromise in terms of speed and cost of analysis, taking into consideration the features of the MS analyzers. 

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