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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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