Background: Contamination of pesticide to human is difficult to detect, especially in low concentration setting. So we need to
develop a technique that accurately detect the types and amount of common pesticides in Thailand.

Objective: To investigate 35 pesticides in five major classes consist of organophosphorus, organonitrogen, pyrethroid
organochlorine and fungicide by using solid phase micro extraction (SPME) vial headspace followed by gas chromatography mass spectrometry (GC-MS).

Materials and Methods: An experimental study based on solid phase micro extraction (SPME) vial headspace followed by gas
chromatography mass spectrometry (GC-MS) was developed for the determination of 35 pesticides in plasma.

Results: Types of fibre coating were tested, 50/30 μm Polydimethylsiloxane/Divinylbenzene/Carboxen (PDMS/DVB/CAR) showing higher recoveries of the compound. The main factors affecting the SPME process, such as adsorption and desorption times (40 and 5 min, respectively), incubation temperature (70°C), NaCl addition were optimized. The procedure was validated in terms of linearity r2>0.995 for concentrations ranging from 0.05 to1.0 μg/mL, intra and interday precision % CV <15, sensitivity was 0.02 μg/mL for
LLOQ and % recovery >85% to <120%.

Conclusion: HS-SPME in combination with GC-MS is an effective method for the determination of 34 of 35 pesticides (except abamectin) in human plasma and shows a great potential for using in rapid on-site analytical work, which may be needed in clinical toxicology.

Keywords: Pesticide, Solid phase micro extraction, SPME, Gas chromatography mass spectrometry, GC-MS