CONICET | Buscador de Institutos y Recursos Humanos

Abstract In the chromatographic trace analysis of complex matrices, small sample size, simple sample preparation, good sensitivity and full automation are all highly desirable characteristics. Large volume injection (LVI) and on-line coupled liquid chromatography-gas chromatography (LC-GC) have become powerful tools in an attempt to achieve these goals. LVI increases sensitivity and/or reduces the need for extract concentration steps. In coupled LC-GC, the specific components of a complex matrix are pre-fractionated by LC and then transferred on-line to the highly efficient and sensitive GC system for analytical separation. The problem with both techniques is basically the same: how to introduce into the GC system a volume of a liquid sample, extract or eluent from LC, far above that usually injected in GC. In order to achieve this, reliable interfaces, if possible automatic, which allow the solvent to be eliminated and analytes to be retained without loss or contamination, are necessary. For such a purpose TOTAD (Through Oven Transfer Adsorption Desorption) was designed: this interface allows the LVI of polar and non-polar solvents and, consequently, on-line LC-GC when LC is carried out in normal as well as in reversed phase. The TOTAD interface is based on a thoroughly modified PTV injector, the changes introduced in the same affecting its pneumatics, sample introduction and solvent elimination. An eluent from an LC system can be sent to the interface or to waste by a six port valve. When sent to the GC system, the eluent passes through the liner. This is filled with an adsorbent or absorbent material, which retains the analytes while the eluent is eliminated to waste through a stainless steel tube situated on the external side of the liner, pushed by helium flowing in an opposite direction to the GC column carrier gas flow. The eluent is vented in both evaporative and non-evaporative mode. During the transfer, the interface and oven temperature are kept low and after the transfer, the TOTAD interface is rapidly heated and the retained analytes are thermally desorbed and transferred to the GC column. Main modifications made to the initial interface, previously unpublished, are explained. Different analytical methods by LVI and RPLC-GC using the TOTAD interface have been developed. LVI with TOTAD interface allows the analysis of pesticides in river water by sampling volumes as large as 1 ml. LVI of vegetables extracts obtained with a small amount of ethyl acetate and anhydrous sodium sulphate allows pesticide residues to be analysed. If pesticide residues have to be analysed in samples of a fatty nature, such as olive oil or nuts, the coupling of RPLC and GC using the TOTAD interface can effectively separates the fatty compounds in the RPLC step. Olive oil simply needs to be filtered before the chromatographic analysis. In the analysis of nuts, pesticides are extracted with a small amount of ethyl acetate and anhydrous sodium sulphate, and the extract is directly injected in the chromatographic system with no need for concentration or clean-up steps. An automated method for the analysis of unsaponifiable compounds in edible oils has also been developed. The method allows the analysis of different groups of compounds (free sterols, tocopherols, squalene and erythrodiol and uvaol) in one chromatographic run or the analysis of these compounds in different groups. A method for analysing methyl-jasmonate in aromatic samples by RPLC-GC has been developed. All the above methods practically eliminate the time-consuming sample preparation step, present high sensitivity and good repeatability. No variability in the retention time is observed, which can be a problem in other LC-GC coupling systems. Good performance is achieved at different eluent and helium flow rates during the transfer step. TOTAD is a versatile and fully automatic interface highly suitable for LVI and on-line NPLC-GC and RPLC-GC coupling.

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