Lim T.B*, Chanbasha B., Lee H.K, Michael Tay Ming Kiong
Southeast Asia Environmental Forensics Symposium, 19-21 Sept 2005, Taipei, Taiwan. (oral presentation)
Recently, there have been interesting developments in the use of hollow fibre membranes for liquid-phase microextraction (LPME) of trace organic analytes in aqueous matrices. In contrast to conventional liquid-liquid extraction (LLE), hollow fibre-based LPME employs single porous hollow fibres made of polypropylene as support for organic solvents, which are used as the extracting medium. The hollow fibres are inexpensive and disposable.
The experimental set-up is very simple, economic and easily improvised in the laboratory. In our hollow fibre-based device, 6 to 10 µL of organic solvent was impregnated in the lumen of a porous hollow fibre, the top of which was fitted over the needle tip of a 10-µL micro-syringe. The solvent-filled fibre was subsequently immersed in an aqueous sample containing target analytes. Since the extracting solvent is confined in the lumen, the sample solution can be stirred without significant loss of solvent. After extraction, the solvent was retracted from the lumen into the micro-syringe and analysed directly by chromatographic techniques.
In forensic examinations of trace evidence, organic substances in small amounts and low concentrations often encountered. This trace evidence can provide a crucial link between the suspect and the crime. Gas chromatography with mass spectrometry (GC/MS) is a method of choice for the sensitive and unequivocal identification of many organic compounds. The technical challenge often lies in sample preparation and sample clean-up, that is, the efficient extraction and concentration of trace levels of organic substances from a matrix.
This project explored the application of hollow-fibre LPME to representative target compounds among polyaromatic hydrocarbons (PAHs) and pyrethroid insecticides in aqueous matrices. PAHs are a large group of organic compounds widely distributed in the atmosphere, whose molecular structures contain two or more aromatic rings fused together. The main sources of PAHs are vehicle emissions, natural fires, cigarette smoke, soot and other residues from the incomplete combustion of carbon-based fuels. PAHs absorbed onto airborne particulate matter contaminate rain and together with deposition of particulate matter end up in surface water, soil and plants. Soot samples containing PAHs are often encountered in cases of arson and suspicious fires.
Pyrethrins are naturally occurring pesticidal chemicals derived from the chrysanthemum flower. Pyrethroids are a family of insecticides that are synthetic analogues of the pyrethrins. Synthetic pyrethroids are widely used to control many common pests and their domestic use has increased substantially in recent years. Cases of adulteration of drinks and food by insecticides have been encountered frequently in domestic disputes.
This project studied the extraction efficiencies of PAHs and pyrethroids from dilute aqueous solutions using hollow-fibre LPME by varying the stirring rate, extraction time, pH, salt concentration, and using pure as well as mixtures of different extracting solvents. The reproducibility of hollow-fibre based LPME was also investigated by studying the linearity of different spiked concentrations of analytes in aqueous solution.