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Based on a standard instrument
The new 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). Zenobi explains that "such measuring instruments
are routinely used in many areas nowadays." 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 newly-developed 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.
Equipment modification in less than an hour
Professor Zenobi says "There is nothing special about the new method
from a technical viewpoint." Huanwen Chen, who has 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.
Numerous possible applications
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 sport.
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