Comprehensive two-dimensional gas chromatography
Comprehensive Two-dimensional gas chromatography, or GC×GC is a multidimensional gas chromatography technique that was originally described in 1984 by J. Calvin Giddings and first successfully implemented in 1991 by Professor Phillips and his student Zaiyou Liu. GC×GC utilizes two different columns with two different stationary phases. In GC×GC, all of the effluent from the first dimension column is diverted to the second dimension column via a modulator. The modulator quickly traps, then "injects" the effluent from the first dimension column onto the second dimension. This process creates a retention plane of the 1st dimension separation x 2nd dimension separation. The Oil and Gas Industry were early adopters of the technology for the complex oil samples to determine the many different types of Hydrocarbons and its isomers. Nowadays in these types of samples it has been reported that over 30000 different compounds could be identified in a crude oil with this Comprehensive Chromatography Technology (CCT). The CCT evolved from a technology only used in academic R&D laboratories, into a more robust technology used in many different industrial labs. Comprehensive Chromatography is used in forensics, food and flavor, environmental, metabolomics, biomarkers and clinical applications. Some of the most well-established research groups in the world that are found in Australia, Italy, the Netherlands, Canada, United States, and Brazil use this analytical technique. Modulation: The process In GC × GC two columns are connected sequentially, typically the first dimension is a conventional column and the second dimension is a short fast GC type, with a modulator positioned between them. The function of the modulator can be divided into basically three processes: continuously collect small fractions of the effluent from 1D, ensuring that the separation is maintained in this dimension; focus or refocus the effluent of a narrow band; to quickly transfer the 2D fraction collected and focused as a narrow pulse. Taken together, these three steps are called modulation cycle, which is repeated throughout the chromatographic run. Thermal modulation The most frequently used type of modulation is the thermal modulation (patent holder is ZOEX Corporation), where liquid nitrogen is used to (cryogenic) trap (immobilize) all the components eluting from the first dimension. After a fixed time interval a hot stream pulse is mobilizing a part of the compounds again. This hot pulse can be considered as the injection starting point into the second dimension column. The latest version is called a loop-type Thermal modulator where the released compounds are trapped and refocused for a second time (and released again) to have perfect peak shapes and maximum resolution in the second dimension. With the thermal modulator, very volatile compounds can be modulated. The thermal modulation in practice is a liquid nitrogen cooled loop system that provides the lowest temperature for thermal modulation, and modulates the widest range (C2 to C55) of organic compounds. The temperature at the jet is -189 °C. The maximum temperature of the hot jet is 475 °C. Even methane has been modulated with liquid nitrogen cooled gas jets like those in