Results

A new strategy to analyze volatile organic compounds from icy environments

This contribution presents an original analytical system for studying volatile organic compounds (VOC) coming from the heating and/or irradiation of interstellar/cometary ice analogues (VAHIIA system) through laboratory experiments. The VAHIIA system brings solutions to three analytical constraints regarding chromatography analysis: the low desorption kinetics of VOC (many hours) in the vacuum chamber during laboratory experiments, the low pressure under which they sublime (10−9 mbar), and the presence of water in ice analogues. The VAHIIA system which we developed, calibrated, and optimized is composed of two units. The first is a preconcentration unit providing the VOC recovery. This unit is based on a cryogenic trapping which allows VOC preconcentration and provides an adequate pressure allowing their subsequent transfer to an injection unit. The latter is a gaseous injection unit allowing the direct injection into the GC-MS of the VOC previously transferred from the preconcentration unit. The feasibility of the online transfer through this interface is demonstrated. Nanomoles of VOC can be detected with the VAHIIA system, and the variability in replicate measurements is lower than 13%. The advantages of the GC-MS in comparison to infrared spectroscopy are pointed out, the GC-MS allowing an unambiguous identification of compounds coming from complex mixtures. Beyond the application to astrophysical subjects, these analytical developments can be used for all systems requiring vacuum/cryogenic environments.

Optimizations of recovery and chromatographic seperation of volatile organic compounds from vacuum environments

The gaseous phase analyses of volatile organic compounds (VOCs) are an important challenge especially when these organics are formed in high vacuum environments (10 −8 mbar) reproducing the environ- ment 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 diver- sity 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 −8 mbar) and their transfer at higher pressure to the injection unit of a GC for their subsequent analyses. This system showed suffi- cient 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 al- lows 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.

Volatile organic compounds generated from the VUV photoprocessing of methanol ices

Next to water, methanol is one of the most abundant molecules in astrophysical ices. A new experimental approach is presented here for the direct monitoring via gas chromatography coupled to mass spectrometry (GC-MS) of a sublimating photoprocessed pure methanol ice. Unprecedentedly, in a same analysis, compelling evidences for the formation of 33 volatile organic compounds are provided. The latter are C1–C6 products including alcohols, aldehydes, ketones, esters, ethers and carboxylic acids. Few C3 and all C4 detected compounds have been identified for the first time. Tentative detections of few C5 and C6 compounds are also presented. GC-MS allows for the first time the direct quantification of C2–C4 photoproducts and shows that their abundances decrease with the increase of their carbon chain length. These qualitative and quantitative measurements provide important complementary results to previous experiments, and present interesting similarities with observations of sources rich in methanol.

Impact of ice composition on gas phase abundances of volatile organic compounds

In support of space missions and spectroscopic observations, laboratory experiments on ice analogs enable a better understanding of organic matter formation and evolution in astrophysical environments. Herein, we report the monitoring of the gaseous phase of processed astrophysical ice analogs to determine if the gaseous phase can elucidate the chemical mechanisms and dominant reaction pathways occurring in the solid ice subjected to vacuum ultra-violet (VUV) irradiation at low temperature and subsequently warmed. Simple (CH3OH), binary (H2O:CH3OH, CH3OH:NH3), and ternary ice analogs (H2O:CH3OH:NH3) were VUV-processed and warmed. The evolution of volatile organic compounds in the gaseous phase shows a direct link between their relative abundances in the gaseous phase, and the radical and thermal chemistries modifying the initial ice composition. The correlation between the gaseous and solid phases may play a crucial role in deciphering the organic composition of astrophysical objects. As an example, possible solid compositions of the comet Lovejoy are suggested using the abundances of organics in its comae.