RESUMO
Effects of microfiltration membrane adsorption for eight types of pesticides with diverse physicochemical properties on direct injection liquid chromatography-tandem mass spectrometric method ( DI-LC-MS/MS) were investigated. The results showed that the adsorption effects ( AE,%) on the loss of signal detection at concentration of 2. 5 μg/L ranged from 8%-92%, 0%-81% and 2%-59% for nylon (NYL), polyethersulfone ( PES) and hydrophilic polypropylene ( GHP) membrane, respectively ( accumulated volume of feed is 1 mL). The pesticides with higher octanol-water partition coefficient (lgKow) values appeared to adsorb onto the membrane surface more readily than those with lower lgKow. The AE was found to be alleviated as the feed volume of samples increased to 10 mL, except the case of profenofos adsorption on PES membrane ( AE=9%) . The effects of PES membrane on the eight pesticides at initial individual concentration of 0 . 25 , 2. 5 and 25 μg/L were also studied. The results showed that, the lower the initial concentration of pesticides, the stronger adsorption effect under the same filtration conditions was obtained. Besides, it was effective in eliminating the membrane adsorption effects by adding 40% methanol ( V/V) into water samples as a modifier, which could consequently improve the accuracy of DI-LC-MS/MS.