Flame ionization detector construction

The activity tests of the catalyst were carried out in a microflow reactor set-up in which all the high temperature parts are constructed of hastelloy-C and monel. The reactor effluent was analyzed by an on-line gas chromatograph with an Ultimetal Q column (75 m x 0.53 mm), a flame ionization detector, and a thermal conductivity detector. The composition of the feed to the reactor can be varied, besides the temperature, pressure, and space velocity. The influence of the recycle components CHCIF2 and methane was tested by adding these components to the feed. In total five stability experiments of over 1600 hours were performed. In each... 

Figure G1.8.1 Diagram of the sniff port constructed from a laboratory filter (based on Acree et al., 1976 see Acree, 1997) showing the filter pump (with the check ball removed) attached to a humidifier, shut-off valve, and charcoal filter. The vacuum side of the pump is positioned over a flame ionization detector (FID) with the hydrogen gas turned off. The make-up gas helps lift the narrow (<0.2-mm-o.d.) gas chromatography (GC) effluent stream into the much larger olfactometry air stream without loss of resolution, and the 300 ml/min air combustion gas produced by the FID also prevents loss of resolution.

Figure 4-1 shows the construction of a flame ionization detector. 

There are a large number of GC detectors available but the majority of GC separations are monitored by the flame ionization detector (FID), the nitrogen phosphorus detector (NPD), the electron capture detector (BCD) or the katherometer detector (or Hot Wire Detector). Tlie latter is almost exclusively used in gas analysis and rarely used in chiral chromatography and so will only be briefly described here. Furthermore, the FID is used in probably 90% of all chiral analyses. However, before describing the construction and function of each detector the subject of detector specifications needs to be discussed. 

The major changes that are required are the installation of a capillary injector and the addition of make-up gas for the detector. Kits for this purpose are available from lab supply houses, and McMurtrey and Knight [13] have described the construction of a homemade one. The easiest conversion is from packed columns to wide-bore columns [14] Jennings [IS] has discussed the procedure in detail. The conversion is rather simple as a minimum, all one needs are some fittings and tubing. These columns are useable with thermal conductivity detectors [16] as well as flame ionization detectors. 

CoupUng capillary columns to the electron capture detector is not without problems. Unlike the flame detectors, relatively large detector cells are common due to certain constructional features of the ionization detectors housing a radioactive source. The use of a scavenger gas or a detector miniaturization are the currently used remedies to this problem. The miniaturization approach is obviously more attractive due to the concentration-sensitive nature of the detector, as already discussed above. 

In the absence of full sets of standards PA concentrations in food or plant samples can be estimated from calibration curves constructed from one or a few available PAs, or less frequently PANOs. Other PAs can be measured against these external standards and described in terms of equivalents of the standard alkaloid. This approach is compromised without correction for the different response factors. In GC-MS the quantification of PAs against a different external standard is possible using flame ionization detection, although response factors differ between open-chain and cyclic esters, and the use of nitrogen specific detectors is preferred. 

---