Ethylene measurement

Ethylene is a gaseous ripening hormone for fruits and plants. When they ripen, they emit ethylene and when they are exposed to ethylene, they start to ripen. The amount of ethylene that is emitted depends on the state of ripening. Thus, the concentration of ethylene gas in a container corresponds directly to the state of ripening and is therefore fundamental for monitoring the quality of climacteric fruits.

In situ measurements directly in fruit containers during transportation have been hampered by the lack of portable units that sustain the rough conditions in a container and that detect ethylene in the ppb (parts per billion) range.

During the project, a miniaturised gas chromatograph was developed, which was able to detect ethylene at very low concentrations, below 50 ppb. A commercial gas sensor was used together with two newly developed components:

• The resolution was improved by a preconcentrator device. During the adsorption phase, ethylene is accumulated in eight channels, each filled with Carbosieve SII® as a stationary phase. The silicon walls between the channels were used as a heater for the desorption process to release the ethylene. Thus, the sensitivity of the system was indirectly increased. Without the preconcentrator, the detection limit of the gas sensor was 100 ppm and with the preconcentrator this limit of detection was increased by a factor of 2000. As further advantage, the preconcentrator automates the sampling process.
• The applied gas detector is sensitive to multiple gases. Particularly, the high humidity in containers (approx. 98%) has an impact on the gas sensor that leads to variable output signals. To eliminate cross-selectivities to other gases, a miniaturised gas chromatography column was developed. 
• In tests under laboratory conditions, Carbosieve SII® was found to be the best suited stationary phase for the column. Components of the gas sample are separated from each other in the column and thus they arrive at the gas sensor at different times. With the knowledge of the retention time, every peak in the output signal can be assigned to a specific gas component.

The complete gas chromatograph system is much smaller than standard laboratory devices. It consists of the miniaturised preconcentrator, the miniaturised gas chromatography column and a sensor element. The functionality of the system has been proven under laboratory conditions. Field-tests are at the planning stage.