Full scan GC-MS quantitation of pesticides in spring water at the 10 ppt level using large volume on-column injection

AT-column, a novel concentrating technique for large-volume injections in gas chromatography

Nowadays, large-volume injection is widely used for the GC determination of trace analytes, specifically to improve detectability. The most popular injectors for large-volume injections are the programmable temperature vaporisation (PTV) injector and the cold on-column (COC) injector, where each device has its own advantages and limitations. The novel AT-column concentrating technique combines features of two other injection techniques, loop-type large-volume and vapour overflow. AT-column injection is based on solvent evaporation in an empty liner with solvent vapour discharge via the split line. Little or no optimisation is required. The only relevant parameter is the injection temperature which can easily be calculated using the equation of Antoine. As an application, AT-column injection is combined with GC-MS for the trace-level determination of labile analytes and with GC-flame ionisation detection for the analysis of high molecular weight polymer additives. In summary, AT-column is an injection technique that combines the inertness of the COC, and the flexibility and robustness of the PTV large-volume technique.

Picogram determination of "earthly-musty" odorous compounds in water using modified closed loop stripping analysis and large volume injection GC/MS

"Earthy-musty" off-flavor problems in water samples are due to organic compounds present at the sub-part-per-trillion level. Numerous analytical methods such as purge and trap, liquid/liquid extraction, and closed-loop stripping analysis (CLSA) followed by GC/MS analysis have been used to determine these compounds. However, these methods offer poor sensitivity (detection limits of approximately 1 to 10 ng/L) when compared to the 20-30 pg/L of sensorial sensitivity. The purpose of this study was to develop a new method involving a modified CLSA preconcentration technique together with large volume injection GC/MS in order to attain analytical sensitivity equal to or better than olfactory sensitivity. For eight target compounds that cause taste and odor problems in water at trace levels, the method developed was linear in the 0.05-10 ng/L range and provided recoveries greater than 70% together with satisfactory repeatability. Detection limits as low as 15-30 pg/L were achieved, representing a 50-fold improvement in sensitivity as compared to current methods. The accuracy and sensitivity of the method were demonstrated in different aqueous matrixes, including raw surface water. The method was successfully applied to earthy-musty water samples that had remained unsolved by conventional techniques, thus proving its effectiveness.

On-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection to determine pesticides in water

A group of pesticides with different chemical structures was determined in water by on-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection through an on-column interface. A 10 mm x 2 mm I.D. precolumn packed with PLRP-S was selected for the solid-phase extraction process. The parameters affecting the transfer of the analytes from the precolumn to the GC system (e.g. flow-rate, temperature and solvent vapor exit time) were optimized. An organic modifier was added to the sample before the extraction process to avoid adsorption problems. The use of the MS detector under selected ion monitoring acquisition enabled the analytes to be quantified at sub microgram-per-litre levels preconcentrating only 10 ml of sample, and the limits of detection (S/N = 3) were between 2 and 20 ng l-1. The method was applied to the determination of the pesticides in tap and river water, and molinate was determined in Ebro river water.