Investigations on analyte losses in systems suited for large-volume on-column injections

Abstract

Use o~ a large-volume injection system with a solvent vapour exit (SVE) requires optimisation. An appropriate strategy is to determine the evaporation rate by increasing the injection time at a fixed injection speed, injection temperature and head pressure. When measuring the flow rate in the carrier gas supply line to the on-column injector, optimisation can be very rapid: some five injections of pure solvent will be sufficient.When working under pa~ially concurrent solveni evaporation conditions, loss of volatiles is often observed if no retaining precolumn is used be~een the retention gap and the SVE. To investigate the requirements (length anct stationary phase) of the retaining precolumn, C8-C18 n-alkanes in n-hexane were used. The minimum length of the retaining precolumn (0.32 mm diameter) needed to prevent substantial losses of volatiles was 2 m. Experiments with retaining precolumns with ancl without stationary phase gave identical results. This shows that there is no need to coat the capillary as it only acts as a restrictor.

The selection of the standard phase (gas vs. liquid) and the related matrix effect on the direct injection gas chromatographic analysis of VOCs at sub–ppm levels

“…In analysis of L-WS using direct liquid injection at high temperature, a combination of a direct injection (DI) liner and program temperature vaporizing can provide high sample transfer efficiencies to the GC column to decrease sample losses (Ouyang et al, 2005). To facilitate LVI and limit sample loss (e.g., loss of volatiles), modifications to the injection system is required; e.g., by applying partially concurrent solvent evaporation process (PCSE) combined with an on-column injector and a retention gap (e.g., deactivated fused silica) (Adahchour et al, 2001). …”

Injectors for capillary gas chromatography and their application to environmental analysis

“…Although a pre-column of 3 m is generally used, a number of studies have shown that it really acts as a restricting pre-column, eliminating the precolumn can increase the carrier gas flow through the retention gap thus increasing the evaporative rate. 26,47 The COC provides no separation of analytes from co-injected matrix components 17 and COC inlets thus have the lowest tolerance to coinjected matrix components followed by pulsed splitless or splitless mode. The PTV with solvent split technique has the highest tolerance for matrix components.…”

Safety Assessment of Recycled Plastics from Post-Consumer Waste with a Combination of a Miniaturized Ames Test and Chromatographic Analysis

“…As no single analytical method is able to identify all detected substances at the moment [13][14][15], especially in complex matrices like recycled plastics, an optimization of current testing schemes is urgently needed. As the physico-chemical properties of genotoxins regarding their hydrophobicity and volatility can be quite diverse [16], a combination of analytical methods is necessary to detect a broad spectrum of possible DNA-reactive, mutagenic substances. That said, even such a combination will not result in a complete identification, as analytical reference standards are not yet available for all compounds, especially for as yet unknown NIASs [17].…”