Multidimensional and Comprehensive Two-Dimensional Gas Chromatography

Abstract

The analysis of many complex samples requires a performance which conventional one-dimensional (1D) GC cannot provide. In multidimensional GC (MDGC) selected fractions of the GC eluate are online subjected to a second GC separation. This is a useful technique when only one, or a few, target analyte has to be determined. When, however, wide ranging screening has to be performed or the detection/identification of unknowns is of particular interest, MDGC becomes extremely time-consuming and cannot really solve the analytical problems. Comprehensive two-dimensional GC (GC×GC) should now be used. Here the entire sample is subjected to two (independent) separations, using a very rapid (2–8 s) second-dimension separation in order not to lose the resolution achieved on the first column. The total run time is therefore essentially the same as with a conventional 1D separation! The set-up of a GC×GC system is discussed and attention is given to (1) the interface between the two GC columns, the (cryogenic-type) modulator, which effects the trapping of each subsequent first-column eluate fraction and its rapid relaunching onto the second column, and (2) detection, usually with a ToF MS, micro-ECD or FID detector which provide the high data acquisition rate necessary because of the fast second separation. Applications deal with the analysis of food, fragrances, biological, environmental and air/aerosol samples, and petrochemical products, and with the trace analysis of many classes of organohalogens. The much improved analyte-from-analyte as well as analytes-from-interfering background separations, the creation of ‘ordered structures’ which facilitate analyte classification, improved detectability, and reliable (ToF MS-based) identification are highlighted.