**5. Detectors**

After separating the compounds, a detector is used to monitor the outlet stream from the column. Detection in analytical microsystems is a subject of paramount importance. Indeed, detection has been one of the main challenges for analytical microsystems, since very sensitive techniques are needed as a consequence of the ultrasmall sample volumes used in micronsized environments.

The flame ionization detector (FID) is the most popular and widely used detector for the analysis of trace levels of organic compounds. Its success is based on outstanding properties, such as a very low minimum detectable limit, a high sensitivity, and a broad linear measurement range. Kuper's team works on miniaturized planar FID since 2000 where the oxygenhydrogen flame burns inside a glass-silicon chip (**Figure 14**) [45].

At the opposite of FID, thermal conductivity detector (TCD) is a nondestructive system. It measures the difference in thermal conductivity between pure carrier gas and the carrier gas

**Figure 14.** Left: Photography of a micro-FID on a PCB adapted from [47], right: A suspended micro-TCD, adapted from [48].

contaminated with the sample components. Miniaturization of TCD started with the first micro-GC in 1979, and since then several studies have been published in this area [46, 47].

Many sensors such as chemiresistor array and metal oxide (MOX) sensors have been reported for chip-based GC. The response mechanism of these sensors mainly relies on the impedance changes. Typically, a chemiresistor consists of a conductive or semiconductive polymer or emulsion and organometallic compounds [48, 49].
