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A multiresidue gas chromatography-tandem mass spectrometry (GC-MS/MS) method was developed for the analysis of 159 multiclass pesticides in tobacco. A modified QuEChERS sample preparation technique, based on acetonitrile extraction and toluene dilution, followed by dispersive solid-phase extraction (d-SPE) cleanup using primary-secondary amine (PSA) and octadecyl (C18) sorbents, was used for sample treatment. Key performance parameters investigated were linearity, recovery, relative standard deviation (RSD), limit of detection, and limit of quantitation. With the exception of chinomethionate and folpet, recoveries for pesticides ranged from 69 to 141%, and the RSDs ranged from 2 to 27%. The validated method was applied to the analysis of 118 real samples, and positive results were obtained for 116 samples, with 25 different pesticides being detected.

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A simple and sensitive high performance liquid chromatography-tandem mass spectrometry (HPLC-ESI-MS-MS) method was developed and validated for the quantification of creatinine in human urine. The analysis was carried out on an Agilent Zorbax Eclipse XDB-C18 column (2.1 × 150 mm, 3.5 μm). The mobile phase was 0.1% formic acid in water and 0.1% formic acid in acetonitrile (50/50, v/v). Linear calibration curves were obtained in the concentration range of 1–2000.0 ng/mL, with a lower limit of quantification of 0.99 ng/mL. The intra- and interday precision (RSD) values were below 3%. The method was successfully applied to a bioequivalence study of creatinine in Chinese smokers and nonsmokers. The total cotinine in 24 h urine and cotinine : creatinine ratio were also positively associated (Pearson R = 0.942, P < 0.0001). However, cotinine : creatinine ratio varied significantly across smoking groups for the difference of individual. 24 h urinary cotinine was more appropriate for expressing correlation with tar than cotinine : creatinine ratio.

A method for the determination of three acidic herbicides, dicamba, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in tobacco and soil has been developed based on the use of liquid-liquid extraction and dispersive solid-phase extraction (dispersive-SPE) followed by UPLC-MS/MS. Two percentage of (v/v) formic acid in acetonitrile as the extraction helped partitioning of analytes into the acetonitrile phase. The extract was then cleaned up by dispersive-SPE using primary secondary amine as selective sorbents. Quantitative analysis was done in the multiple-reaction monitoring mode using stable isotope-labeled internal standards for each compound. A separate internal standard for each analyte is required to minimize sample matrix effects on each analyte, which can lead to poor analyte recoveries and decreases in method accuracy and precision. The total analysis time was <4 min. The linear range of the method was from 1 to 100 ng mL(-1) with a limit of detection of each herbicide varied from 0.012 to 0.126 ng g(-1). The proposed method is faster, more sensitive and selective than the traditional methods and more accurate and robust than the published LC-MS/MS methods.