Screening Method for Multiclass Antibiotics

A recent review (Diaz-Cruz 2006) has summarized recent work on determinations of antibacterial residues in aquatic matrices (and gives useful information on structures and MS/MS fragmentations characteristic of each compound class), but with only brief mention of multiresidue methods covering more than one class of such compounds. However, an example of a multi-residue anal5dical method (Hao 2006) was developed for determination of 27 target compounds, including 18 commonly 

A QqQtiap mass spectrometer (Section 6.4.6) was used in conventional triple quadrupole MRM mode for routine quantitation, but in some experiments this was combined using the information dependent acquisition (IDA) software facility function with the ion trap function for identification of unknowns and/or confirmation of target analytes. Only one MRM transition was monitored for each analyte, thus gaining only 2.5 identification points rather than the specified three (European Commission 2002, see Table 9.1) this was undoubtedly a consequence of the large number of analytes monitored in this multiresidue analysis. A retention time within 5 % of the standard value determined for pure analytes in distilled water was also a required criterion (Hua 2006) for confirmation of identity. 

As emphasized previously (Section 8.4), while the EPA MDL does have the attribute of transparency and some level of connection to confidence limits at a stated confidence level, it has several disadvantages including its dependence on the value of the arbitrarily chosen concentration used to determine its value. This problem is also evident in this work (Hao 2006), which also estimated quantitation limits (LLOQs) for the target analytes as follows. Serial dilutions of the extract solution used in the MDL determination were analyzed until the S/B value for one or more analytes feU to 5 1. The LLOQs of the 

As a result of the design of multi-residue methods for such purposes, they are intrinsically prone to provide false positive results. A good example is provided by work designed to monitor residues of some macrolide antibiotics as well as some steroid hormones (Schliisener 2005) in unfiltered influents and effluents of sewage treatment 

An interesting recent example (Castiglioni 2006) describes an LC-ESI-MS/MS method for the determination of the illicit drugs cocaine, amphetamines, morphine, cannabinoids, methadone and some of their metabolites in wastewater (both treated and untreated). Quantitation was achieved in the low ng.L range, with overall variability 10%. Cocaine and metabohtes, amphetamines, morphine and metabolites, methadone and its main metabolite, and 11-nor-9-carboxy-A9-tetrahydrocannabinol (the main metabolite of tetrahydro-catmabinol), were aU measured in significant amounts in influents and effluents of two wastewater treatment plants, indicating possible environmental risks to pubhc health. 

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