Determination of penicillins in milk of animal origin by capillary electrophoresis: is sample treatment the bottleneck for routine laboratories?

Capillary electrophoresis (CE) is increasingly being used not only for research purposes but also for routine analyses. The latter, however, are especially difficult when the analytes are present at very low concentrations in complex food samples (e.g. penicillins in milk of animal origin). No study of the difficulties encountered in daily practice in sample treatments for the determination of penicillins (PENs) in milk by CE has to our knowledge been reported. Rather than reviewing the main uses of CE for determining PENs in different types of samples, this paper focuses on the weaknesses of available methods for this purpose, which originate in sample treatment rather than in a lack of robustness of the CE technique. Some problems which, based on our own experience, often confront sample treatment and method development in this context are discussed here. Clearly, the greatest source of error in this context is sample processing, which must provide optimal extraction and preconcentration of analytes, and extracts compatible with the separation technique to be used. In this respect, using time-consuming procedures can cause the loss of variable amounts of analytes in different steps. Interestingly, dramatically simplifying the sample preparation process can detract from sensitivity but lead to increased recoveries. As with any methodological development in routine analysis, acceptable results can only be obtained by considering all potentially influential factors.