Determination of active components in insecticide formulations by liquid chromatography and resolution of overlapped peaks by multivariate analysis and derivative spectrophotometry

In liquid chromatography, complex mixtures of pesticides may show peaks with a great overlap under the experimental conditions commonly used. The use of partial-least squares (PLS) regression and derivative spectrophotometry makes it possible to discriminate between the spectral bands of the overlapping chromatographic solutes, taken from peaks with co-eluting species. In this paper, a procedure for the determination of insecticides in commercial formulations by using a diode-array spectrophotometer as chromatographic detector has been devised. The procedure consists of two steps. In the (first) chromatographic step, the active component peak (corresponding to fenitrothion or permethrin) which is isolated in time is determined by conventional liquid chromatography; the appropriate conditions permit to remove also the interference from solvents in the commercial formulations. In the (second) multivariate step, partial-least squares regression is applied to the overlapped spectra of the co-eluting components (piperonyl butoxide-neopynamine or dicofol-tetradifon). This method makes it possible to analyze compounds showing appreciable overlap of their chromatographic peaks, without modification of the experimental variables used.