The Two Options for Sample Evaporation in Hot GC Injectors:  Thermospray and Band Formation. Optimization of Conditions and Injector Design

Abstract

Although classical split and splitless injection is more than 30 years old, we only start to understand the vaporization process in the injector. Solvent evaporation determines much of the process and is the first obstacle to overcome. Videos recorded on devices imitating injectors showed that sample (solvent) evaporation is often a violent process which is poorly controlled and might well explain many of the puzzling quantitative results often obtained. We do not adequately take into account that two vaporization techniques are in use. Partial solvent evaporation inside the syringe needle (optimized as "hot needle injection") produces thermospray: the sample liquid is nebulized upon leaving the needle. The resulting fog is rapidly slowed and moves with the gas. Solute evaporation largely occurs from microparticles suspended in the gas phase. Empty liners are most suitable. Fast autosamplers suppress vaporization in the needle, i.e., nebulization, and shoot a band of liquid into the chamber that must be stopped by a packing or obstacles suitable to hold the liquid in place during the 0.2-5 s required for solvent evaporation. Solute evaporation largely occurs from the surfaces onto which the sample is deposited. Insights into these mechanisms help optimize conditions in a more rational manner. Methods should specify whether they were optimized and validated for injection with thermospray or band formation. The insights should also enable a significant improvement of the injector design, particularly for splitless injection.

Validation of Two Methods for Fatty Acids Analysis in Eggs

“…As the split injection mode used was optimized in this study, discrimination was not expected. Split injection at 250°C and a split rate of 1:50 is recommended as the preferred injection technique, especially in vaporizing injectors, since it is the main source of error in quantitative analysis of the long-chain saturated fatty acids (internal standards) to a different extent to PUFAs [24]. In addition, on-column injection as well as optimized split injection produced accurate results for PUFAs [22].…”

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

“…(3 μL)>81 819 (5 μL). Such trend in RF values in liquid standard calibration may be explained by a number of factors (e.g., changes in matrix/analyte ratio, degradation of instrumental sensitivity, and volumetric expansion of L-WS to cause solvent vapor effect) (Grob and Biedermann, 2002;Kim and Nguyen, 2007;Hoh and Mastovska, 2008;Kim and Kim, 2012b). However, in both standards, the highest RF values [207 864 (gas) and 187 794 (liquid)] were obtained at the lowest injection volumes [50 (gas) and 1 μL (liquid)], respectively.…”

Recent trends in the advanced analysis of bioactive fatty acids

“…Nevertheless, the procedure leaves the possibility to apply other injection techniques such as on-column injection. It has also been suggested that the injection technique, especially in vaporizing injectors, is the main source of error in quantitative GC [235]. Discrimination effects inside the injector are mainly caused by different volatilities of analytes.…”