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Waterloo Science

Chemistry Research

Dr. Tadeusz Górecki - Research


Comprehensive 2D-GC
The number of substances that can be separated on a single column is limited by so-called peak capacity. Under ideal conditions, it can be several hundred at the most. In practice, this number is usually much lower because peaks are not evenly spaced. Peak capacity can be increased dramatically by performing the separation in more than one dimension. Application of comprehensive two-dimensional chromatography for the analysis of complex samples in the field and in the laboratory is therefore studied. In this method, analytes eluting from one column are trapped for a short time in a special interface and re-injected into a second column with a different stationary phase. Separation in the second column is very fast, so that all components leave the column before subsequent injection takes place. 
We have developed several simple interfaces for GCxGC with no moving parts. Their performance is comparable to that of much more complicated designs described in the literature. We have also introduced a new mode of GCxGC operation, so-called stop-flow GCxGC. The system developed has been coupled to a time-of-flight MS for the analysis of complex environmental samples (e.g. endocrine disruptors in waste water, pyrolysis products, air particulate matter, etc.). 

Passive sampling
Volatile analytes can be collected from the atmosphere using many different methods. One of the most attractive approaches is passive sampling, which requires no power, complicated sampling devices, etc. In permeation passive sampling, analytes from the air diffuse through a semi-permeable membrane and are trapped by a sorbent. The total amount of the analyte collected by the sampler is proportional to its time-weighted average concentration in the air. Until recently, each permeation sampler had to be calibrated for each individual analyte to produce quantitative results. We have developed a method which allows calibration to be carried out based on physico-chemical properties of the analytes (e.g. boiling point, chromatographic retention index, etc.). This allows permeation samplers to be deployed in the same way as conventional sorbent-based active samplers.

Extraction of volatile analytes from low-permeability media
Numerous industrial sites are contaminated by chlorinated solvents (VOCs) in the subsurface. At many locations, the solvents occur in low-permeability media such as clayey deposits and fractured sedimentary rocks. Extraction of VOCs from core samples is currently the slowest step in the analytical procedure aimed at determining VOC concentrations. With conventional solvent extraction, it might take as long as several weeks to reach steady concentration of the analyte(s) in the extract. We have developed several extraction methods that dramatically reduce this time. They are based on microwave-assisted extraction or a combination of sonication with mechanical agitation of the samples. The extraction time could be reduced to less than an hour per sample.

Non-discriminating pyrolysis
High molecular weight fragments produced during pyrolysis often carry the most significant structural information, yet they cannot be detected using commercial pyrolysis system because of analyte discrimination on transfer to the GC column. New pyrolysis technique was developed to overcome this problem. Pyrolysis is carried out in disposable segments of deactivated stainless steel capillary tubing, heated at a very high rate (~50,000°C/s) by capacitive discharge. To facilitate transfer of very high-boiling analytes to the GC column, the pyrolysis capillary is subject to thermal desorption immediately following the initial heating pulse. Pyrolysis of polyethylene using the new method yielded the characteristic alkadiene/olefine/alkane pattern reaching as far as C-73 (M.W. 1020/1022/1024). The method allowed the detection of hopanoids (hopane hydrocarbons, hopanic acids, hopanols) in the pyrolyzate of humic organic matter, peat and some bacteria. Other applications, including environmental analysis, are being studied.

Field analysis
Determination of organic compounds directly on-site has very significant advantages over sampling in the field and analysis in the laboratory. Composition of a sample may change during transport and/or storage due to volatilization, adsorption on the container walls, absorption by improperly selected container materials, or biodegradation. The results obtained in a laboratory are only of "historic" value, which makes it difficult to make decisions based on them, especially in emergency situations. We are developing methods for field analysis of PCBs in soil based on ion-mobility spectrometry (IMS) and dry electrolytic conductivity detection (DELCD).

 

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