08/07/09 Thermo Fisher Scientific Inc., the world leader in serving science announces another significant gain in laboratory productivity highlighted in a new application note. Combining the low detection levels achievable with the Thermo Scientific ITQ 700 GC-ion trap mass spectrometer with a QuEChERS sample preparation method allows laboratory scientists to greatly enhance sample throughput without sacrificing levels of detection. This milestone is highlighted in the company's latest application note "Multi-residue Pesticide Analysis in Green Tea by a Modified QuEChERS Extraction and Ion Trap GC/MSn Analysis" which details how to perform accurate, dependable multi-residue pesticide analysis in green tea following sample preparation using the QuEChERS method.

Recently-formulated pesticides are smaller in molecular weight than their predecessors and are designed to break down rapidly in the environment. As a result, to successfully identify and quantify these compounds in foods, more careful consideration must be placed on the sample preparation for extraction and the instrument parameters for analysis. The QuEChERS sample preparation method, published recently as AOAC Method 2007.01, has considerably simplified the determination of pesticides in fruits, vegetable, grains and herbs.

The study was performed by coupling the ITQ 700 with the Thermo Scientific FOCUS GC gas chromatograph in order to determine the linear ranges, quantitation limits and detection limits for a partial list of pesticides that are commonly used on green tea crops. Samples were prepared in matrix using the QuEChERS sample preparation guidelines for analysis by gas chromatography/tandem mass spectrometry (GC/MSn) on the ITQ 700. Caffeine and polyphenols were removed from the samples prior to injection. A Thermo Scientific TRACE TR-Pesticide III 35% diphenyl/65% dimethyl polysiloxane column was chosen to improve the resolution of the more polar compounds.

A single splitless injection of 22 pesticides was performed with detection in electron ionization (EI) MS/MS. Multiple matrix spikes were analyzed at both high and low levels to verify the precision of the analytical method.

The MS/MS scan mode offered significantly enhanced selectivity over scanning modes such as full scan and selected ion monitoring (SIM). The ITQ 700, operated in the MS/MS mode, generated unique product ion spectra by collision-induced fragmentation of each of the detected pesticides. Because of the highly effective elimination of matrix interfering ions, more accurate results were produced at the lower levels.