Researchers from the Swiss Federal Institute of Technology (ETH) modified a standard QTOF mass spectrometer for a new purpose: diagnostic scanning of surfaces, including those of living organisms.
The press statement from ETH explains the research from a group led by Renato Zenobi, Professor of Analytical Chemistry at the Organic Chemistry Laboratory:
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.
Zenobi says “There is nothing special about the new method from the technical viewpoint.” Huanwen Chen, who developed the method as a post-doc in Zenobi’s group, demonstrated this impressively when he and Zenobi presented the new method to a company. Within one hour, Chen modified their mass spectrometer so it could be used to analyse the surface of objects of any kind.
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.” Zenobi is convinced that the method could also become an important tool in the field of food quality monitoring. “It takes only a few seconds to measure a single sample; so large numbers of random samples can be analysed routinely.” For meat samples the scientists were also able to show that the sample material does not even need to be thawed. For example, the modified mass spectrometer can detect traces of putrescine and cadaverine (tetra- and pentamethylenediamine) on frozen meat samples. These substances are released as bacterial metabolic products and — as their names indicate — they constitute indicators of defective quality.