Abstract
Abstract Large volume injection (LVI) in gas chromatography (GC) and online liquid chromatography-gas chromatography (LC-GC) are useful techniques for analyzing the compounds present at very low concentrations in complex samples since they substantially increase the sensitivity of the analysis and simplify sample preparation. LVI avoids the need to concentrate the extract and even the extraction step itself by directly injecting the sample. In online LC-GC, the liquid chromatography (LC) step acts as the sample preparation and/or fractionation step. The main problem in both techniques is the selective elimination of the large volume of solvent without losing the analytes. The TOTAD (through oven transfer adsorption–desorption) interface, based on a widely modified PTV (programmed temperature vaporizer) injector, allows large volumes to be injected into the gas chromatograph using both nonpolar and polar solvents, including water. Consequently, online LC-GC can be carried out whether the LC step is in the normal phase or the reversed phase. Various methods for analyzing trace compounds in food and environmental samples have been developed for LVI and online LC-GC using the TOTAD interface. Such analysis methods require the optimization of several variables common to LVI and online LC-GC and specific variables involved in online LC-GC, which must be optimized by taking into account the nature of the analytes and the characteristics of the sample matrix. This article reviews how each of these variables affects the performance of the analysis.
Highlights
When the volatile compounds in a given sample are to be determined, the most sensitive technique and the one with the greatest separation capacity is gas chromatography (GC)
Water samples can be injected directly into the GC, but special conditions are necessary [4] because water can cause hydrolysis of the siloxane bonds of the stationary phase of the chromatographic column, and water is not compatible with some detectors that are frequently used in GC, e.g., mass spectrometry (MS) [5]
It is very important to completely eliminate the solvent remaining inside the capillary tube (CT) because, if some remains in this capillary, the solvent is vaporized when the oven temperature is increased for the GC analysis and the vapor would enter into the GC column
Summary
When the volatile compounds in a given sample are to be determined, the most sensitive technique and the one with the greatest separation capacity is GC. Once the solvent has been totally eliminated, the GC column is connected again, the PTV is quickly heated, and the analytes are transferred to the GC column This procedure allows large amounts of aqueous solvent to be eliminated [44,45] but has the drawback that the column has to be manually removed during the online transfer step, and it is impossible to automate the process. To overcome this problem, a PTV injector was greatly modified, affecting the pneumatics, sample introduction, and solvent elimination in the design of the TOTAD interface
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