New spectrometer method analyses substances on surfaces of any kind
28 September 2007
A new and simple method of adapting a mass
spectrometer enables it to analyse substances on any surface, including
living tissue, rapidly and with no special sample preparation.
The method was developed by a group of researchers led by Renato Zenobi,
Professor of Analytical Chemistry at the Organic Chemistry Laboratory of the
Swiss Federal Institute of Technology (ETH) Zurich. The study is published
in the latest issue of the scientific journal Angewandte Chemie.
procedure of analysis represents a further development of the method
recently published by the group in which the researchers successfully
detected various substances in the breath in a simple manner. Using their
enhanced method, they can now also very precisely track down substances on
surfaces of any kind.
Both methods are based on what is called a
‘quadrupole time-of-flight mass spectrometer’ (QTOF mass spectrometer).
Samples for QTOF mass spectrometry are normally presented in solution. The
solution is electrosprayed, with the additional aid of a desolvation gas.
The tiny droplets give rise to ions that are characteristic of the substance
to be analysed and which the QTOF instrument measures.
The ETH Zurich
researchers have now almost turned the principle on its head: instead of
studying the substances in the solution, they now examine the substances
present in the desolvation gas assisting the spray. With the new method,
nitrogen is blown from a small nozzle onto a sample surface. As the gas
strikes the surface it desorbs semi-volatile substances. The enriched gas
stream is then fed into the mass spectrometer where the absorbed substances
can be precisely analysed.
Rapid spectrometer modification
Professor Zenobi says, "There is nothing special about the new method from a
technical viewpoint." Huanwen Chen, who developed the method during his
post-doctoral studies in Zenobi’s group, impressively demonstrated this when
together with his supervisor he presented the new method to a company.
Within one hour Chen had modified their mass spectrometer so that it could
be used to analyse the surface of any kind of object.
However, the remarkable aspect of the new method is the wide variety of
possibilities it opens up. "One particular strength of our approach is that
even the surfaces of living organisms can be examined. It only takes a few
seconds to measure a single sample; so large numbers of random samples can
be routinely analysed," Zenobi says. For meat samples the scientists were
also able to show that the sample material does not even need to be thawed.
The studies carried out by the researchers on
the skin of various test persons lead in quite a different direction. Traces
of nicotine, coffee and explosives could all be detected on the skin.
According to Zenobi, "The method’s strength is that it is fast and
non-invasive, and needs no special sample preparation."
In view of the numerous possible applications, it is not surprising that
the new method is of interest not only to foodstuffs technologists and
safety experts but also to medical professionals and drugs investigators in
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