A 3D printed cryogenic device for gas chromatography: Design, and performance demonstrated for multidimensional and enantioselective separations

Abstract

This paper describes the development of a device 3D printed using stainless steel that is intended to operate as a cold trapping assembly when cooled by liquid CO₂, in a manner similar to a longitudinally modulated cryogenic system (LMCS). The cold trap enclosure design is detailed, and the system's performance is tested to assess its suitability for use as a collection and rapid re-mobilisation device for gas chromatography analysis of volatile organic compounds (VOC). Precision of modulation period timing was evaluated, showing a maximum error of 8 μs and an average variation of <1 ns across 10,000 successive modulations. The system's trapping capabilities were tested using an alkane series (C₅-C₉), successfully trapping all analytes and producing peaks with full width at half height (FWHH) as low as 65 ms. Maximum trapping time was assessed for hexane, with the modulator retaining the compound for up to 9 s in a 100 °C oven before breakthrough was observed. The modulator was then applied to investigate enantioselective separation of limonene. Whilst a single chiral column was used, various lengths (20 cm – 5.0 m) of column were drawn through the modulator, where these lengths effectively function as enantioselective second dimension (²D) columns. Injected (R,S)-limonene enantiomers were collected as a single entity, then rapidly released to the ²D column. Comprehensive two-dimensional gas chromatography was demonstrated to be viable using the 3D printed modulator for a tea tree oil sample.