ORIGINAL PAPER Kwenga Sichilongo Enhanced signal generation for use in the analysis of synthetic pyrethroids using chemical ionization tandem quadrupole ion trap mass spectrometry Received: 8 July 2004 / Revised: 8 September 2004 / Accepted: 21 September 2004 / Published online: 5 November 2004 Ó Springer-Verlag 2004 Abstract Synthetic pyrethroids fragment extensively under electron ionization (EI) conditions to give low mass ions, most of them with the same m/z ratios. This fragmentation is primarily due to the labile ester linkage found in these compounds. In this research we estab- lished the best gas chromatography (GC) conditions in the EI mode that served as a benchmark in the devel- opment of a chemical ionization (CI) protocol for ten selected synthetic pyrethroids. Based on proton affinity data, several reagent gases were evaluated in the positive CI ionization mode. Methanol was found to produce higher average ion counts relative to the other gases evaluated, which led to the development of an optimized method consisting of selective ejection chemical ioniza- tion (SECI) and MS/MS. Standard stainless steel ion trap electrodes produced significant degradation of chromatographic performance on late eluting com- pounds, which was attributed to electrode surface chemistry. A dramatic improvement in signal-to-noise (S/N) ratios was observed when the chromatographi- cally inert SilcosteelÒ coated electrodes were used. The resulting method, that has significant S/N ratio improvements resulting from a combination of septum programmable injections (SPI), optimized CI and inert SilcosteelÒ-coated electrodes, was used to determine instrument detection limits. Keywords Pyrethroids Æ Chromatography Æ Tandem mass spectrometry Æ Electron ionization Æ Chemical ionization Æ Mass-to-charge Introduction Synthetic pyrethroids, which are synthetic analogs of pyrethrins (extracts of Chrysanthemum cinerariafolium [1]), are more photostable than pyrethrins and are widely used as insecticides. Pyrethroids show excellent efficacy when used for agricultural purposes (10 g active ingre- dient/ha) [2]. They are non-persistent insecticides with low mammalian toxicity, which reduces user/applicator risk. However, pyrethroids exhibit very high toxicities toward aquatic life. Typical pyrethroids are synthesized through the esterification of a pyrethroid acid such as chrysanthemic acid and an alcohol such as 3-phen- oxybenzyl alcohol [3]. One problem with separating pyrethroids using gas chromatography (GC) is related to their very high boiling points, resulting in very late chromatographic elution. Even with high column temperatures, co-elution of different pyrethroids is often observed. In order to prevent condensation of the analytes and peak broad- ening after elution, temperatures that are higher than the final temperature need to be used for the transfer line. The mass spectral analysis is complicated by the exten- sive fragmentation that is observed in the electron ion- ization (EI) spectrum. This fragmentation has been associated with the labile ester linkage found in all py- rethroids. This fragmentation results in low mass ions which often have the same mass-to-charge ratios as ions from other members of this class of compounds. To surmount these obstacles, an alternative approach to traditional methods is required. Several methods [4–19] have been used for the determination of synthetic pyrethroids and their metabolites. GC–MS is attractive due to its speed and sensitivity. In addition, when a three-dimensional quadrupole ion trap (QIT) mass spectrometer is used as the detector, tandem mass spectrometry (MS/MS) be- comes feasible. When tandem mass spectrometry is ap- plied to trace level determinations, it greatly increases selectivity and simplicity even when dealing with com- plex matrices, thus affording low detection limits. The precursor ion in a tandem experiment needs to be of relatively high mass and abundance in order to obtain a product ion mass spectrum of analytical significance and to achieve a good signal-to-noise (S/N) ratio and sub- K. Sichilongo Department of Chemistry, The University of Zambia, P.O. Box 32379, Lusaka, Zambia E-mail: ksichilo@natsci.unza.zm Anal Bioanal Chem (2004) 380: 942–949 DOI 10.1007/s00216-004-2864-y