Automated on-line GPC-GC-FPD involving co-solvent trapping and the on-column interface for the determination of organophosphorus pesticides in olive oils

The robustness of an automated on-line GPC-GC-FPD method for the determinat ion of Organophosphorus (OP) Pesticides in olive oil has been significantly improved, now allowing a routine operation. The original GPC-GC transfer t echnique employed a loop type interface with an early vapor exit and co-sol vent trapping. Shooting, caused by boiling delay and malfunctioning of the solvent vapor exit during the transfer of the 3 mt solvent fraction to the retention gap, resulted in insufficient focusing of the OF-pesticides. In t his interfacing concept, the GPC fraction is introduced directly into the c arrier gas stream during a certain time interval using the Dualchrom pressu re- and flow regulation, resulting in a very stable transfer The interface now basically corresponds to an on-column interface with now regulation. Vi a a Pyrex glass door behind the GC-oven door it can be seen that the liquid flow is broken up into alternating gas-liquid segments by the carrier gas flow during transfer. This avoids shooting in the retention gap and broaden s the temperature range for successful transfer. By using a smaller sized G PC column the solvent fraction transferred was reduced to 1.3 mit. Methyl a cetate/cyclopentane and the co-solvent n-nonane were selected for their low er boiling points. The modified method is very robust and has been applied to the analysis of 28 different OF-pesticides in olive oil with an overall detection limit of 0.002 mg/kg. Routinely 24h of unattended operation is po ssible with a cycle time of 75 min.