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 peak s with a great overlap under the experimental conditions commonly used . The use of partial-least squares (PLS) regression and derivative spe ctrophotometry makes it possible to discriminate between the spectral bands of the overlapping chromatographic solutes, taken from peaks wit h co-eluting species. In this paper, a procedure for the determination of insecticides in commercial formulations by using a diode-array spe ctrophotometer as chromatographic detector has been devised. The proce dure consists of two steps. In the (first) chromatographic step, the a ctive component peak (corresponding to fenitrothion or permethrin) whi ch is isolated in time is determined by conventional liquid chromatogr aphy; the appropriate conditions permit to remove also the interferenc e from solvents in the commercial formulations. In the (second) multiv ariate step, partial-least squares regression is applied to the overla pped spectra of the co-eluting components (piperonyl butoxide-neopynam ine or dicofol-tetradifon). This method makes it possible to analyze c ompounds showing appreciable overlap of their chromatographic peaks, w ithout modification of the experimental variables used.