http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-49NRNJ1-5&_user=10&_coverDate=12%2F12%2F2003&_alid=690928813&_rdoc=1&_fmt=summary&_orig=search&_cdi=5248&_sort=d&_docanchor=&view=c&_ct=1&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=73a3b295326781eb23d43a558b9c4a45

Abstract
A new method was developed for the analysis of pesticide residues in tobacco. The objective was to significantly increase the number of samples that can be processed by the laboratory and to enable the extension of the current coverage to additional pesticides. A new analytical approach was therefore defined based on two main axes, the automation of the sample preparation and the selectivity of the analyte detection using tandem mass spectrometry. This latter aspect reduces the stringency of the requirements placed on the clean-up of the extracts and on the chromatographic resolution when less selective detectors are used. The extraction of the analytes from the matrix is performed using the pressurized liquid extraction technique. Tobacco samples are extracted at elevated temperature and pressure (100 °C and 100 atm; 1 atm=101,325 Pa) using acetone as an extraction solvent. The resulting extract is then concentrated using a Vortex evaporator. Three different solid-phase extraction (SPE) procedures, adjusted to the chemical properties of the different active ingredients to be measured, are applied to the concentrated extract, thus leading to three extract fractions. The first fraction contains such main classes of active ingredients as organohalogenated and 2,6-dinitroaniline compounds while the second one collects the organophosphorus and acylalanines residues; these two fractions are analyzed by capillary gas chromatography coupled to tandem mass spectrometry using negative chemical ionization and electron impact ionization in the positive mode, respectively. The third extract fraction gathers the N-methylcarbamates residues which are analyzed by HPLC with post-column derivatization and fluorescence detection. The different sample preparation stages from extraction to SPE clean-up have been automated through the use of recent analytical technologies. In combination with the analysis by tandem mass spectrometry, this provided a potential for a high sample throughput. 
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3.5. HPLC determination of N-methylcarbamates
The N-methylcarbamates contained in the third SPE eluate were analyzed by HPLC with post-column reaction and fluorescence detection. This analytical approach is widely used for N-methylcarbamates in complex matrices as indicated in a review published by Yang et al. One paper describes the application of this analytical approach for the determination of N-methylcarbamate residues in tobacco. The data gathered in the context of the global assessment
of the method (see Tables 3–5) indicated that the quantification at three levels (0.05, 0.5 and 3 ppm) was accurate and precise. The recoveries ranged from 99 to 106% at the 3 ppm level, from 92 to 105% at the 0.5 ppm level and from 80 to 113% at the 0.05 ppm level. The relative standard deviation (R.S.D.) determined under repeatability conditions (n = 6) ranged between 1.1 and 7.4% at the 3 ppm level, between 1.9 and 8.1% at the 0.5 ppm level and between 3.3 and 14% at the 0.05 ppm level.