Analysis of Organophosphorus and Organonitrogen herbicides in water using GC/MS with selected ion recording
Laboratories monitoring trace level pesticides and herbicides by gas chromatography/mass spectrometry (GC/MS) frequently utilize Selected Ion Recording (SIR) techniques to maximize analytical sensitivity for quantification. With analytical standards, precision is limited to a large extent only by the autosampler and other instrumental effects. However, real-world samples pose a greater challenge. In this latter case, matrix effects have a detrimental effect on both sensitivity and precision.
Often, such analyses are carried out using on-column injection, as classical (hot) splitless injection can result in the loss of thermally labile species. The practical disadvantages of on-column injection usually manifest themselves in the form of degraded separation and peak tailing as the retention gap rapidly becomes contaminated with matrix components. Chromatographic performance may be restored by cleaning or replacement of the retention gap, but this is time consuming and requires a significant level of operator skill.
In programmed splitless injection the sample is introduced into a cool (quartz) injector liner packed with quartz or silanized glass wool. The packed liner has a much greater sample capacity than the retention gap used in on-column injection methods. After injection, the temperature of the injector is rapidly heated to transfer the analytes to the head of the chromatographic column. This approach exposes the sample to substantially milder conditions than the flash vaporization used in classical splitless injection. It eliminates possible decomposition caused by contact of the analytes with a heated metal syringe. Another advantage of this approach is that the same experimental setup may also be used for large-volume injection with solvent purging.