Analysis Of Methomyl In Rat Plasma And Study On Detection Of Its Metabolite By Mass

ObjectiveFor the purpose of more accurate and rapid analysis of methomyl in plasma,a solid phase extraction-reversed-phase high performance liquid chromatography (SPE-HPLC) method was developed and the high performance liquid chroma-tography-mass (HPLC-MS) method was used in the detection of methomyl and its metabolite in rat plasma.MethodsThe sample pretreatment method,the test conditions,the linear range,the sensitivity,the specificity,the precision,the accuracy,the stability and the recov-eries for the plasma were investigated by using rat plasma spiked with standard methomyl and internal standard substance,and a accurate and rapid SPE-HPLC method was developed in the final;methomyl and its metabolite were determinated in the rat plasma by SPE-HPLC-MS.After the intragastric administration with methomyl by 5mg/kg,the rat plasma was collected at 0.33h,0.67h,1h,2h,3h,5h,7h,9h,11h,13h,15h,17h,19h,21h,23h, methomyl was determinated in the rat plasma by SPE-HPLC;In the simulated medicolegal investigation,after the intragastric administration with methomyl by 50mg/kg,all the rats were caused dead,the carcases of rats were kept for 72 hours in room temperature,then the heart-blood was get and methomyl was determinated in the rat plasma by SPE-HPLC;the assay was conducted on the kromasil C₁₈(4.6mm i.d.×250mm,5μm) column with methanol-water(40:60) as the mobile phase.The detection wave length was set at 235nm and the diazepam was taken as the internal standard.In the simulated medicolegal investigation,after the intragastric administration with methomyl by 50mg/kg,all the rats were caused dead,the carcases were kept for 72 hours in room temperature,then the heart-blood was get,methomyl and its metabolite were determinated in the rat plasma by SPE-HPLC-MS;the assay was conducted on the Xterra C₁₈(2.1mm i.d.×150mm,5μm) column with methanol-water(15:85)as the mobile phase.The detection wave length was set at 235nm.A mass spectrometer equpied with Electrospray ionization source in the positive mode was used with a N₂ flow rate of 450L/h,a N₂ temperature of 300℃,an ion source temperature of 110℃,an ESI needle voltage of 3.0kv,a scan range of 50-300 m/z.ResultsThe linear range was 0.1μg/ml-20μg/ml(r=0.999 3,P＜0.001),The limit of detection was 0.03μg/ml(S/N=3).The intra and inter-day precisions of assay for methomyl were less than 8.33%and 11.11%in blood respectively.The intra and inter-day accuracy of assay for methomyl were between 90%and 120%in blood respectively.The recovery for methomyl was more than 88%±4.4%in plasma.In the simulated medicolegal investigation,methomyl and its metabolite were found in rat plasma at 72 hours of poisoning with methomyl.The metabolite was identified as S-methyl-N-hydroxythioacetamidate.ConclusionThe method for quantitative and qualitation analysis of methomyl is rapid, accurate and The metabolite was identified,which is suitable for the identification of methomyl in the cases with suspected methomyl poisoning in medical and forensic science.