Optimization and application of the PTV injector for the analysis of pesticide residues

The applicability of PTV splitless and solvent vent injection to the gas ch romatographic analysis of 26 pesticides representing different chemical cla sses was evaluated. All parameters related to optimum injector performance in PTV splitless and PTV solvent vent (split vent) injection modes were tes ted. For PTV splitless injection of small sample volumes (1 muL), the inlet temperature program (initial inlet temperature, heating rate, final temper ature), splitless time, and starting oven temperature were optimized. Param eters identified as optimal were then applied in PTV solvent vent injection . In the case of the PTV solvent vent technique, all injections were perfor med with pesticides dissolved in a binary mixture of cyclohexane-ethyl acet ate (1:1, v/v). This solvent is used as a mobile phase in the HPGPC clean-u p step involved in our multiresidue method. For the PTV solvent vent techni que the following parameters were tested: maximum single injection volume, inlet temperature, vent flow, vent time, and vent period were determined fo r a single injection of 10 muL of sample. Thermodegradation and/or adsorpti on of some pesticides occurred as long as glass wool packed liner was used. To achieve lower detection limits, multiple injection concept was employed : 30 muL of standard solution were injected in three subsequent steps. Unde r optimized conditions even higher sample volumes could be injected. Good r esponses were obtained also for the compounds possessing relatively higher volatility compared to other tested analytes.