New method reveals substances on surfaces o...( Last August German police discovered...)

Last August German police discovered about 50 tons of rotten meat on the premises of a wholesaler in Bavaria. Because the risk of rotten meat turning up in grocery stores everywhere is not to be underestimated, the importance of efficient food quality monitoring is clear.

However, reliable measurement methods that enable large numbers of samples to be analysed quickly and economically would need to be in place in order to make comprehensive monitoring a reality. In the latest issue of the scientific journal Angewandte Chemie, the group led by Renato Zenobi, Professor of Analytical Chemistry at the Organic Chemis-try Laboratory of ETH Zurich, has presented a method that successfully meets these requirements.

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 sub-stances 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 en-riched gas stream
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