Low Cost Gas Chromatography Using Sensor Array for Food Screening

Modern food production involves many complex processes that need to be controlled to ensure food safety and food quality.

Gaschromatographiesystem
© FhG IME
Scheme of the measuring system: 1 sampling, 2 drying agent, 3 tempered separation column, 4 sensor array, 5 evaluation software
Metalloxid Sensor vom Fraunhofer IPM
© FhG IPM
Metal Oxyd Sensor Fraunhofer IPM
Chromatogramm
© FhG IME
Top: GCMS chromatogram of the target substance after 48 h incubation. Down: Sensor chromatogram of the target substance after 6 h incubation. The other peaks represent laboratory cleaning agents.

The proliferation of national and international guidelines, ordinances and laws on food quality and safety means that stricter controls through governmen­tal agencies and/or in-house quality assur­ance systems (Hazard Analysis Critical Control Point, HACCP-concept) are required. This frequently involves time-consum­ing and expensive intermediary steps, since indi­vidual production processes have to be monitored analy­tically in the control labora­tory.Such controls generate additional financial bur­dens that disproportionately affect small and me­dium enterprises.

So-called on-line methods, integrated into the produc­tion process, save time and money, but are currently restricted to measuring the simplest chemical and physical parameters such as pH and tempera­ture. More complex systems are under development, but are not yet reliable enough for commercial application.

Aim

In cooperation with the Fraunhofer Institute for Physical Measurement Techniques (IPM) a robust and cost effective gas sensor array for the rapid detection of volatile compounds should be elaborated in the scope of a Fraunhofer Research Project. The gas sensor array is intended for application in various areas of food industry:

  • Incoming goods control
  • Process control
  • Storage and transport.

Project description

We used commercially available, inexpensive metal oxide sensors (Fig. 1), which are already used in waste gas and ventilation controls, and in fire detectors and combined them into a system that follows the principles of gas chromatography. Unlike alternative systems with a similar role (so-called electronic noses), this system uses a chromatographic separation column which splits a gas mixture and feeds the sensors with the individual substances (Fig. 2).

In the first project phase, the single components were selected according to the analytical requirements. In the second project phase, proof of prin­ciple was established by combining the components into a complete system.

Results

Initial tests were carried out with stand­ard substances, and our bespoke metal oxide sensors were tested against com­mercial sensor arrays. The four stand­ard substances could be detected within six minutes (gas chromato­gra­phy would normally take 45 minutes). Although the reproducibility of the sensor test was comparable to the reference analysis, the sensitivity was up to ten-fold higher.

Further experiments were carried out to address practical issues, such as the detection of bacterial contamination, which was achieved considerably faster by the application of volatile metab­olites than using traditional microbio­logical techniques. In our approach, the volatile metabolites were identified using headspace gas chromatography. In a second step, the experimental approach was transferred to the sensor system. The results are presented in Fig. 3.