Advanced Techniques for Organic Analysis

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The main thrust of the research will be the advancement of high efficiency and multidimensional separations, including comprehensive two-dimensional gas chromatography (GC×GC) and liquid chromatography (LC×LC). The goals of the research include increasing the speed and efficiency of the separations through unconventional approaches. Passive sampling of volatile organic compounds in air will be further developed with a particular focus on soil gas analysis. We have developed a novel thermal modulator for GC×GC requiring no cryogens or moving parts. It is based on a segment of deactivated stainless steel tubing coated with a proprietary coating consisting of silica nanoparticles obtained through thermal treatment of polydimethylsiloxane (PDMS). We will attempt to significantly increase the capacity of the coating through incorporation of carbon-based nanomaterials characterized by large surface areas and high sorption capacities. These will include nanodiamonds, which are extremely mechanically and thermally stable and have the highest heat conductivity of all materials, as well as graphene/graphene oxide, known for very high sorption capacity and high thermal stability. We also plan to explore sol-gel chemistry to incorporate the nanomaterials and increase the amount of the active phase inside the modulator. Modern small particle columns in HPLC provide very efficient separations, but require very high pressures to drive the mobile phase. We will explore a new class of stationary phase particles developed by Dr. Eric Prouzet from the University of Waterloo, which combine sub-micron size with very high intermediate porosity, making them very permeable. We expect columns packed with these particles to offer exceptional efficiency at relatively modest backpressures. Applications of these columns in environmental analysis will be explored. LC×LC remains a technique under development, especially in its on-line version. We will use our experience gained in the area of GC×GC to advance the technique. In particular, we will focus on increasing the speed of second-dimension separations through the use of very short (but highly efficient) columns packed with the nanoparticles described above. Very fast gradients will be used, generated with the help of proprietary microfabricated mixers of extremely low volume. We will also explore the use of thermal modulation in LC×LC. Preliminary results on the suitability of the approach reported by other groups look very promising, and our expertise in the area of thermal modulation should be an unquestionable asset. There is a growing need for inexpensive tools for the characterization of soil gas at polluted sites. PDMS-based permeation passive samplers developed by our group have been adopted for this purpose with some success, but their performance suffers in low permeability media because of the starvation effect. We plan to develop a novel approach to soil gas analysis based on equilibrium sampling. A glass rod coated with a relatively thick layer of PDMS will be exposed to the soil gas using a specially designed probe. After a sufficiently long time the PDMS coating will reach equilibrium with the surrounding atmosphere, and the concentration of the analytes in the coating will be proportional to their concentration in the soil gas. The probe will allow isolating the sampler from the atmosphere for retrieval. The sampler will then be transferred to a thermal desorption tube containing a sorbent for transport to the laboratory. Any analyte that could potentially desorb from the PDMS during transport will be trapped by the sorbent, hence integrity of the sample will be preserved. If successful, this method has a tremendous potential for commercialization.