Quantitative analysis of pesticide residues in tea by gas chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization.

In this study, gas chromatography-tandem mass spectrometry (GC-MS/MS) using an atmospheric pressure chemical ionization (APCI) source was applied for the quantitative analysis of pesticide residues in tea. To determine the optimum ionization conditions for multiresidue analysis, the full-scan mass spectra and peak intensities of pesticides were compared in the presence and absence of water as a modifier. When water was added as a modifier in the ion source, most of the target compounds formed [M+H]+ ions and exhibited enhanced intensities. However, compounds consisting of only carbon, hydrogen, and chlorine, such as aldrin, γ-hexachlorocyclohexane, and p,p'-dichlorodiphenyldichloroethane, typically formed M+· or fragment ions, whose intensities were significantly decreased by the addition of water. GC-MS/MS methods using APCI (without modifier addition) and electron ionization (EI) were validated for 16 pesticides in tea at spiking levels of 0.01 and 0.1 mg/kg. Unlike EI, signal suppression was observed for most compounds at a spiking level of 0.01 mg/kg using APCI; however, dilution of the samples minimized this effect. Using APCI, the trueness of the target compounds ranged from 77% to 121% at both spiking levels, except for pyrethrins owing to matrix effects, with relative standard deviations of less than 14%. For most compounds, these results were comparable with those obtained using EI. However, because the use of APCI limited fragmentation, this ionization technique offered significantly higher sensitivity and specificity than EI. Using APCI, linear calibration curves with coefficients of determination greater than 0.998 were obtained in the range of 0.0005-0.5 μg/mL for all compounds. These findings indicated that GC-MS/MS with APCI is applicable for the routine monitoring of pesticide residues, even in complex samples such as tea.