Automated solid phase dynamic extraction - Extraction of organics using a wall coated syringe needle

Extractions of liquid samples were carried out using wall coated needles pr epared from stainless steel capillary columns instead of syringe needles. T his micro extraction technique was applied to the analysis of pesticides in water. Important parameters influencing the extraction such as sample velo city, extraction time and also the desorption parameters were investigated and optimized. Automation of this technique was realized using a convention al automatic sampler. Limits of detection were im proved using the multiple extraction / desorption technique. Chromatographic data and limits of dete ction were compared with those obtained by solid phase micro extraction (SP ME). Using a needle with a 7 mum film yielded limits of detection varying f rom 0.001-0.1 mug/L and were in the same range as those resulting from the extraction using a 100 mum polydimethyIsiloxane (PDMS) SPME fiber. The main advantages of the needle extraction technique were the significantly highe r extraction speed and the practical aspects of a stable steel needle compa red to those of a fragile fiber. The extraction speed using a needle with a 7 mum film was up to five times higher than the speed of SPME using a 100 mum PDMS fiber. The steel needle could be stressed mechanically in a higher extent than a SPME fiber. Sample volumes and aliquots of liquid media coul d be handled and moved from one bottle to another using the automatic sampl er.