Modifying gas chromatography systems with cryogenic technologies

Researchers at Monash University in Clayton, Australia, have developed a new 3D-printed device for gas chromatography (GC), demonstrating its effectiveness in carrying out multidimensional and enantioselective separations.

GC has long been central to chemical analysis, particularly for mixtures of volatile compounds. However, its resolution can be insufficient for separating complex mixtures. Scientists have addressed this limitation with techniques such as multidimensional gas chromatography (MDGC) and comprehensive two-dimensional gas chromatography (GC × GC), which both require modulation devices. Thermal modulators, among the earliest developed, remain widely used.

In this study, the researchers designed a stainless steel 3D-printed device to function as a cold trapping assembly when cooled with liquid CO₂. Its operational principle mirrors that of a longitudinally modulated cryogenic system (LMCS). Cryogenic technologies have precedent in chromatography, offering the capacity to remobilise trapped components, thereby enabling new analytical approaches. When integrated with GC, such devices allow analysts to apply advanced separation techniques.

The team detailed the enclosure design and assessed its performance for collecting and rapidly remobilising volatile organic compounds (VOCs). Modulation period precision was evaluated, yielding a maximum error of 8 microseconds and an average variation of less than 1 nanosecond across 10,000 successive modulations. Using a C5–C9 alkane series, the system was shown to effectively trap analytes, with peaks achieving a full width at half height (FWHH) as low as 65 milliseconds.

The maximum trapping time was determined using hexane, with the modulator retaining the compound for up to 9 seconds at 100 °C before breakthroughs occurred. The system was also used to investigate the enantioselective separation of limonene, a compound derived from citrus peel oils. Although only one chiral column was used, different column lengths (ranging from 20 cm to 5.0 m) were drawn through the modulator. These effectively acted as enantioselective second-dimension (2D) columns. Injected (R,S)-limonene enantiomers were collected simultaneously and then rapidly transferred to the 2D column. The 3D-printed modulator successfully trapped hexane, enabling modulation periods of up to 8 seconds. This was achieved at oven temperatures of up to 100 °C. While higher temperatures were not tested, the researchers suggest that hexane modulation beyond this point is likely feasible.

Ultimately, the study demonstrated the feasibility of comprehensive two-dimensional GC using 3D-printed modulators with a tea tree oil sample. Although 2D retention times exceeded optimal limits for GC × GC under the conditions tested, the authors propose that further refinement of columns and methods could yield improved separation.

For further reading please visit: 10.1016/j.chroma.2025.466017