AUTOMATED-DETERMINATION OF S-TRIAZINE HERBICIDES USING SOLID-PHASE MICROEXTRACTION

Solid-phase microextraction (SPME) allows the determination of pollutants in aqueous solution by the adsorption of analytes onto stationary-phase coated fused-silica fibres followed by thermal desorption in the injection system of a capillary column gas chromatograph. This technique has been fully automated using a Varian 8100 autosampler and 3409 gas chromatograph fitted with a nitrogen-phosphorus flame thermionic detector. Fibres coated with 7-mu m and 100-mu m film thicknesses were used to evaluate the adsorption and desorption of four s-triazines. The resulting gas chromatographic peaks desorbed from the fibres were shown to be comparable to those obtained with direct manual injection. The 7-mu m fibre, designed for the analysis of semi-volatile analytes was used to investigate the effect of desorption temperature and on-column focusing temperatures on peak response. The desorption temperature was found to be non-critical and an optimum focusing temperature of 40 degrees C was used throughout the analysis. Evaluation of the 100-mu m film fibre demonstrated its potential to adsorb greater quantities of analyte from solution and this study established that an adsorption time of 15 min gave an equilibrium distribution of the solutes between the stationary and liquid phases. With the thicker film fibre it was noted that the effectiveness of the desorption process was reduced at temperatures below 140 degrees C. The linear dynamic range of the technique was evaluated over three orders of magnitude. To enhance method sensitivity, the fibre was used to extract a 0.1 ppb solution of herbicide by repeatedly adsorbing and desorbing from the same solution and focusing the combined solutes at the front of the analytical column prior to elution and analysis.