Effect of extraction conditions and modifiers on the supercritical fluid extraction of 88 pesticides

Supercritical fluid extraction (SFE) conditions for multiresidue analysis of pesticides are evaluated using diatomaceous earth (Celite) spiked with 88 pesticides (16 organochlorine, 33 organophosphorus, 8 pyrethroid, 12 carbamate, and 19 other pesticides). The SFE parameters considered are CO2 density, CO2 flow rate, extraction temperature, static and dynamic extraction times, trap temperature, and addition of modifier. SFE without modifier is insufficient to extract polar pesticides from fortified Celite. The addition of water to Celite is most effective in enhancing the recoveries of pesticides. Methanol is also an effective modifier, but the recovery of captafol, captan, phosmet, and chinomethionat decreases as time goes on after the addition of methanol. The best obtained conditions of SFE (2.0 g sample) are as follows: 0.40 mL of water as a modifier, 0.70 g/mL CO2 density, 50°C extraction temperature, 2.0 mL/min CO2 flow rate, 3.0 min of static extraction, and 20.0 min of dynamic extraction. The extracted pesticides are collected on an octadecylsilane trap at 30°C. Quantitative analysis of the 88 pesticides is performed by gas chromatography-mass spectrometry using the selected ion monitoring mode. Recoveries from fortified Celite are greater than 90% for 79 pesticides and greater than 70% for the other pesticides, except acephale, methamidophos, and propamocarb. The relative standard deviations of the recoveries are less than 5% for almost all of the pesticides.