Automated Solid-Phase Microextraction and Negative Chemical Ionization GC-MS for the Measurement of Synthetic Pyrethroids.

Synthetic pyrethroids are frequently detected as trace contaminants in sediment and natural waters. Because of the importance of measuring both total and freely available concentrations for ecotoxicity evaluations, solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry using negative chemical ionization (NCI-GC-MS) was investigated as an analytical technique. Automated SPME-NCI-GC-MS quantification of freely dissolved (and thus potentially bioavailable) pyrethroids in aqueous samples containing dissolved organic matter (DOM) was successfully applied. The introduction of stable isotope-labeled pyrethroid calibration standards into the water sample allows for the simultaneous determination of total concentrations. Because pyrethroids adsorb rapidly to container walls (especially in calibration standard solutions without DOM) it was necessary to develop a technique to minimize the resulting time-dependent losses from calibration standard solutions in autosampler vials as they await analysis. A staggered preparation of these analytical calibration standards immediately prior to analysis was shown to ameliorate this problem. The developed method provides accurate and reproducible results for aqueous samples containing a range of dissolved organic matter concentrations (e.g., sediment pore water or sediment/water mixtures) and yields practical benefits in comparison to conventional analysis methods, such as reduced sample volume requirements, reduced solvent consumption, and fewer sample manipulations, and makes simultaneous measurements of freely dissolved/bioavailable pyrethroids and total pyrethroids possible.

Quantification of pyrethroids in environmental samples using NCI-GC-MS with stable isotope analogue standards.

Stable isotope internal standards are useful in correcting for matrix effects and instrumental variability when environmental samples such as wastewaters and biosolids are analyzed by mass spectral methods. This paper reports the use of deuterium-labeled analogues of eight pyrethroid insecticides to improve accuracy for the analysis of environmental samples by negative chemical ionization gas chromatography with mass spectrometric detection (NCI-GC-MS). Data for the analysis of effluent water from wastewater treatment facilities are presented which demonstrate that the method is rugged and capable of achieving limits of quantification (LOQs) as low as 0.5 ng/L (ppt), with individual recoveries within the range of 81-94% for those compounds with minimal control background concentrations. In addition, an alternate use of the deuterium-labeled standards is proposed for the determination of method recoveries at low levels that would normally have been precluded due to background pyrethroid levels present in environmental samples being used for control fortifications.