Multiresidue determination of pesticides in fruits and vegetables by liquid chromatography tandem mass spectrometry with on-line sample clean-up technique

A novel on-line sample clean-up and trace enrichment technique was developed for determination of pesticides in fruits and vegetables utilizing liquid chromatography tandem mass spectrometry. This technique uses an on-line solid phase extraction cartridge and column-switching device to reduce tedious off-line wet chemistry operations. The efficiency and recovery of sample preparation is significantly improved.;One hundred and five pesticides with a wide variety of chemical properties are included in the method development of determination of multiresidue pesticides in apple, cucumber, spinach, and tomato. A universal reversed phase high performance liquid chromatography method was used as a separation technique. An Atmospheric Pressure Chemical Ionization (APCI) interface coupled to a triple quadrupole mass spectrometer was employed for detection and quantitation. The ionization mechanisms of the pesticides with different chemical properties in the APCI ion source are discussed. A sensitive multiresidue pesticide screening method using selective ion monitoring (SIM) and selective reaction monitoring techniques (SRM) in both positive and negative modes, was developed. Out of the 105 pesticides studied, 98 in apple, 98 in cucumber, 84 in spinach and 98 in tomato have limits of detection of 10 parts per billion (ppb) or better. All carbamates, organophosphorus and triazines have limits of detection less than 10 ppb. Those pesticides that have high limits of detection are mostly multiple chlorine-containing pesticides, especially chlorinated hydrocarbons. The variables of mass spectrometry that determine the detection sensitivity of pesticides are also discussed. The recovery studies were carried out three times. The average recoveries are 94.7%, 96.6%, 91.8%, and 93.8% for apple, cucumber, spinach, and tomato, respectively. The average relative standard deviations (RSD) of triplicate recovery studies is 5.6% between 1.8% and 12.1%.;Two new concepts of mass spectrometry data acquisition, dynamic selective ion monitoring (DSIM) and dynamic selective reaction monitoring (DSRM) techniques, were created. This is an instrument control computer program designed exclusively on the Finnigan TSQ 7000 system. DSIM and DSRM are techniques which can tolerate retention time drift from run to run without missing pesticide peaks, which often happens in conventional SIM and SRM technique when retention times of peaks shift considerably.