Sensitivity and resolution optimization in gas chromatography coupled to mass spectrometry analyses of volatile organic compounds present in vacuum environment.

The gaseous phase analyses of volatile organic compounds (VOCs) are an important challenge especially when these organics are formed in high vacuum environments (10 mbar) reproducing the environment of astrophysical ices formation and processing. Several analytical techniques have been developed to identify the molecular diversity formed from the processing of these ices. Among them, the coupling of a GC-MS to the vacuum chamber where ices are processed highlighted the interesting chemical diversity of such processed ices. These analyses were possible due to the development of a specific system, the VAHIIA interface that enables the preconcentration of VOCs at low pressure (10 mbar) and their transfer at higher pressure to the injection unit of a GC for their subsequent analyses. This system showed sufficient repeatability (13%) and low detection limits (nmol) for simple ices [1], but presents limits when ice mixtures are complex (such as multi-component ices including water, methanol and ammonia). In this contribution, we present the optimization of our previous VAHIIA system by implementing a cryofocusing system in the GC oven and by improving the recovery yield of VOCs from the vacuum chamber to the VAHIIA interface. The cryofocusing provides an improvement of efficiencies leading to higher resolution and signal to noise ratio, while the addition of argon in the vacuum chamber during the VOC recovery allows increasing the amount of molecules recovered by a factor of ∼200. The coupling of both approaches provides an increase of sensitivity of a factor ∼400. At the end, experiments on astrophysical ices are shown demonstrating the interest of such optimizations for VOC analyses.