Temperature-dependent solute retention time variations, base-line drifts, and solute peak splits during the analysis of fenvalerate by a high-performance liquid chromatography/diode array system

The optical isomers of fenvalerate, (RS)-alpha-cyano(3-phenoxyphenyl)methyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate, were analyzed by high-performance liquid chromatography (HPLC) on chiral columns eluted with mixtures of 2-propanol in hexane. The HPLC eluates were monitored by a photodiode-array ultraviolet absorbance detector. When the HPLC columns were maintained at ambient temperature, chromatograms with drifting base lines of four to eight peaks, instead of four, and isograms, three-dimensional chromatograms, with "negative" peak artifacts coeluted with fenvalerate isomers were usually obtained during a continuous run of the HPLC system for many days and by injecting onto the system only fenvalerate analytical standard solutions. Chromatograms and isograms without artifacts and straight base lines were obtained only when the HPLC column was thermostated and well equilibrated for at least 8-10 h.