TOTAD interface: A review of its application for LVI and LC-GC

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.

What Are We Eating? Surveying the Presence of Toxic Molecules in the Food Supply Chain Using Chromatographic Approaches

“…Methods involving two consecutive chromatographic separations, hereby considered multidimensional (MD) chromatography, have great potential by combining the resolution power of the chromatographic approaches taken individually. However, these formats require sophisticated and expensive instrument configurations and expertise that can be challenging to achieve [127]. Nevertheless, advancements in LC, such as increased orthogonality, separation power, sensitivity, and the ability to hyphenate with more powerful MS detectors, are boosting foodomic investigations, leading to an increase in the number of applications, including food contaminant analyses [128,129].…”

“…Conventional one-dimensional LC cannot resolve potential co-elutions or minimise matrix effects, which can hinder accurate quantitative analysis. However, coupling MD-LC with MS results in a notable enhancement of the separation power or peak capacity, owing to increased selectivity and sensitivity, making it a valuable tool for many applications, such as the quantification of mycotoxins [127]. Mycotoxins are major contaminants in agricultural products, and several other MD-LC approaches have been developed for their analysis, such as a multi LC-LC coupled with the ESI-MS/MS method for the determination of seven mycotoxins in beer [130], or a 2D-LC HRMS method for the simultaneous monitoring of 70 regulated and emerging mycotoxins in Pu-erh tea [131].…”

“…This MD system integrates sample preparation in the first dimension (LC) and analysis in the second dimension (GC). The LC dimension has a high sample capacity, whereas the GC dimension offers a high separation efficiency and the ability to utilise various detectors, including MS. A recent automatised interface, named TOTAD, has been proposed to eliminate manipulation errors and offer different operation modes that enhance analytical performance (e.g., the ability to inject or transfer large volume fractions regardless of the eluent used) [127]. Another promising development in this field is a compact 2D GC system that incorporates microfabricated columns and a nanoelectromechanical system resonator as the detector.…”