Quantitative LC-ESI-MS analysis for pesticides in a complex environmental matrix using external and internal standards

Quantitative liquid chromatography electrospray mass spectrometry (LC-MS) a nalysis for pesticides in a complex environmental matrix using external and internal standard calibration was investigated. Various approaches to intr oducing different internal standard compounds to address quantitative error s associated with signal suppression were also examined. The study involved the analysis of pesticides in wheat hay matrix samples using three kinds o f internal standard compounds: deuterium labeled (D-3) carbon-13 (singly la beled), and structural analogs (derivatives) of the target analytes. Introd uction of the internal standard by volumetric addition and direct post-colu mn infusion were also studied and compared. Isotopically labeled internal standards (i.e. D-3- C-13-) were found to be effective in correcting quantitative errors associated with signal suppress ion. The application of singly labeled C-13 compounds may result in nonline ar calibration due to mass interference with the target analyte species. Th e interference may be compensated by using quadratic curve-fitting or subtr action of the interfering component. Although ineffective as volumetric int ernal standards, structural analogs can be effective in compensating for si gnal suppression when introduced into the LC effluent by continuous post-co lumn infusion. Furthermore, the post-column introduction method allows the application of a single internal standard compound for the quantification o f each analyte in a multi-component mixture. The use of internal standards can be effectively incorporated into residue analysis development methods for pesticides in environmental matrices. High accuracy and reproducibility can be achieved while improving method effici ency by reducing the need for comprehensive sample clean-up.