New method reveals substances on surfaces of any kind

Tuesday 11 September 2007

ETH Zurich researchers have developed a new method that allows even the surfaces of living organisms to be examined quickly and simply. The method opens up interesting new possibilities not only in medicine but also in food quality monitoring.

Based on a standard instrument
The new analysis procedure represents a further development of the method recently published by the group, in which the researchers successfully detected various substances in breath in a simple way. Using their enhanced method, they can now also track down substances very precisely 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 instruments are used routinely in many areas nowadays.” Samples for QTOF mass spectrometry are normally presented as a solution. This is solution is electrosprayed with the additional help of a desolvation gas, and the tiny droplets give rise to ions that are characteristic of the substance to be analysed and which the QTOF instrument measures. The Zurich researchers have now almost turned the principle upside down: instead of studying the substances in the solution, they now examine the substances present in the desolvation gas stream. Whereas in a conventional measurement the spray is generated with pure nitrogen, in their first method the researchers replaced the nitrogen by exhaled breathfrom test persons.. This enabled them to study the test persons’ breath in a simple way.

The newly-developed method no longer needs anyone to blow into the instrument. Instead, nitrogen is blown from a small nozzle onto any kind of sample surface. As the gas strikes the surface it desorbs semi-volatile substances from it. As in the first method, the “enriched” gas stream is then fed into the mass spectrometer where the absorbed substances can be analysed very precisely.

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