METHODS FOR DETERMINING THE VAPOR-PRESSURE OF ACTIVE INGREDIENTS USEDIN CROP PROTECTION - PART V - THERMOGRAVIMETRY COMBINED WITH SOLID-PHASE MICROEXTRACTION (SPME)

The well-established evaporation rate method for determining the vapou r pressure of active ingredients in crop protection down to the order of 10(-12) mbar can be supplemented by the new sample preparation tech nique of Solid Phase MicroExtraction (SPME). With this technique, it i s possible to identify evaporating substances by analysis after partit ioning into the polymer coating of a thin fibre in the outlet-gas flow of thermogravimetric equipment. The active ingredients fenpropimorph, kresoxim-methyl, metolachlor, clomazone and (Z)-9-dodecenyl acetate w ere used in this study, which showed that, despite the relatively smal l amount of collected material, an analytical identification of the ev aporating compound by SPME/GC can be successfully achieved. In particu lar, the experiments have demonstrated a clear correlation between the linearity of the weight loss curve and the evaporation process of a p ure compound. In the case of organic compounds that are unstable to he at, the SPME method can also be utilized to show whether, and at what temperatures, decomposition of the sample into fragments of higher vol atility occurs. For example, the insecticide dimethoate showed a clear temperature dependence of both evaporation behaviour and in the SPME/ GC analysis. (C) 1998 SCI.