Abstract:
This thesis reports on determination of acephate (an organophosphorus used for the control of pests in tobacco, maize, beans etc) in honey. Acephate is a well known brain cholinesterase inhibitor. It is also known to be both toxic and carcinogenic. Acephate carcinogenic properties are believed to come from the active compound methamidophos, from which acephate is prepared. Gas Chromatograph (GC) equipped with capillary column and Thennionic Specific Detector (TSD) was used for the quantitative analysis of acephate in honey. GC conditions were varied to give optimal signal to noise ratio while solvent regime was investigated to give the maximum percentage recoveries of spiked analyte on the honey matrix. Small amount of warm organic free distilled water and acetone were found to be the best extraction solvent system while acetone and dichloromethane mixture in the ratio 8:2 was found to be the best eluant for both silica gel and amine solid phase extraction cartridges clean up. Percentage recoveries for both extraction and cleanup methods chosen for the analysis ranged from 85% to 124% and the detection limit for the method was 1.5 ppb. The best GC conditions found were: air flow rate 110ml/min., hydrogen flow rate 4 ml/min., injection temperature 240°C, isothennal column temperature 150°C and bead current of 3.42A. Detector and auxiliary temperatures were not optimised. The samples investigated were collected from eleven centres in Mbeere district. The observed levels of acephate in honey was compared to maximum residue limit (M.R.L.) and the allowable daily intake (ADI) levels which are both given as 0.03ppm in foodstuffs by World Health Organisation (WHO), Food and Agricultural Organisation (FAO) and Kenya Bureau of Standards (KEBS). The mean concentration of acephate in the samples analysed ranged fi'om very low undetectable values (ND) to 284.56 ppm. It was found that all the eleven honey samples harvested during the dry season had acephate residue concentrations above M.R.L.. 86% of the honey samples collected during the two seasons had acephate concentration in the range of 0.27 ppm to 40.03 ppm, which is above the M.R.L. During the wet season, only three samples out of the eleven analysed were free of acephate residues. All the rest had acephate concentration above the allowed M.R.L requirements.
