In GC analysis, chemical compounds are separated by their interaction with the stationary phase in a GC column. Sometimes, however, the separation is not sufficient to provide identification and/or quantification of all compounds. In many situations involving simple sample analysis, the inability to separate two compounds on a GC column with one stationary phase may be resolved by the use of a different column with a different stationary phase. However, as samples become more complex, the simple substitution of one chromatographic stationary phase for another may result in improvements in separation between some compounds with loss of separation between others. In this situation, the combined separation provided by each of two stationary phases is required. As opposed to limited techniques such as heart-cutting, comprehensive two-dimensional gas chromatography (GC×GC) provides superior chromatographic resolution across the entire sample.
In comprehensive two-dimensional gas chromatography (GC×GC) all of the analyte passes from the first column through the second. Compounds eluting from the first chromatographic column are trapped, and then systematically injected into the second column to obtain the second separation. In order to retain the chromatographic resolution obtained from the first separation, the second orthogonal separation must take place quickly. As such, it is important that compounds be introduced into this column quickly and in a narrow chromatographic band. In the LECO GC×GC system, this is accomplished by cryogenic dual-stage modulation. With cryogenic modulation, compounds eluting from the first chromatographic column are trapped in a narrow zone in the column as it passes through the modulator. When this zone is rapidly heated, the trapped compounds pass into the second chromatographic column as a narrow band, allowing for the highest possible resolution in the second separation.
LECO now offers: In order to properly trap and modulate analytes more volatile than n-octane (C8 n-alkane) the lowest achievable modulation temperatures are required. Reaching these low temperatures requires the use of a cryogen such as Liquid Nitrogen (LN2). LECO’s LN2 modulator delivers the ability to modulate these volatile analytes. However, the use and management of LN2 dewars in a laboratory can be a hindrance to productivity. The Consumable-Free modulator is, therefore, an excellent choice for laboratories hesitant to take on the management of LN2 dewars and who do not require modulation of volatile analytes.