Free Books and Brochures

, employing gas solid chromatography and using a katherometer detector is shown in figure 30. The stationary phase was activated alumina (treated with Fe(OH)2), and the column was 3 m long and 4 mm I.D. The carrier gas was neon, the flow rate 200 ml/min. (at atmospheric pressure) and the column temperature was -196oC. The four detectors described are well established. reliable and generally simple to operate. They are also, probably the most popular. The FID, ECD, NPD and the katherometer are employed in over 90% of all GC applications. The FID is the most versatile, sensitive and linear, and probably the most generally useful. For details of other GC detectors see Gas Chromatography Detectors

nbsp; The Katherometer Detector The katherometer detector (sometimes spelt catherometer and often referred to as the thermal conductivity detector or hot wire detector) is relatively insensitive but has survived largely as a result of its catholic response and, in particular, its response to the permanent gases. Consequently, it is often the detector of choice for gas analysis and environmental testing. Its frequent use in these special types of application, somewhat surprisingly, has made it

archaeological site under investigation at that time.     Figure 61. Total Ion Current Chromatogram of the Lipids from a Potsherd from a Late Saxon Ditch (after ref 22)   C. de St. Etienne and J. Mettes (23) used the GC/MS instrument to assay the purity of silane. Silane of high purity is essential to the electronics industry for the fabrication of integrated circuits and as amorphous silica in photovoltaic applications. The author used a IGC gas chromatograph fitted with a katherometer detector and a packed stainless steel column, 13.2 m long, 3.17 mm I.D., containing Chromosorb PAW 45/60 mesh, coated with 28% of DC 200 stationary phase. Helium was used as the carrier gas at a flow rate of 20 ml/min. The column eluent was split through a low-dead-volume splitter directly to the mass spectrometer. The mass spectrometer was a Riber AQX 156 quadrapole filter having a mass range of 0-300. Electron impact ionization was employed with energies of 70 eV, and the mass

with traces of materials, many of which had strong olfactory intensity and thus confused the olfactory character of the major component. The gas chromatograph had a startling impact on the essential oil industry. Not only was the complex nature of the raw materials disclosed for the first time, but the character of each pure individual components could be accurately ascertained by olfactory assessment of the eluted peaks (using a non destructive detector such as the katherometer, and smelling them). The first separations of essential oils were carried out on packed columns that provided limited efficiency but, nevertheless represented a tremendous advance on distillation. The introduction of the technique of temperature programming improved the separation even more. However, it was not until the capillary column, with its many thousands of theoretical plates, became commercially available that the true complex nature of many of the

column is mixed with a hydrogen, or hydrogen/nitrogen stream, which is then burnt at a small jet and the ions produced measured by an appropriate pair of electrodes. The response of the detector will depend on the mass of solute eluted per unit time from the capillary column and, thus, will be independent of the hydrogen or hydrogen/nitrogen flow (as this will not effect the rate of solute elution, in terms of mass per unit time). In contrast, if the FID was a concentration device (like the katherometer), as the hydrogen or hydrogen/nitrogen flow dilutes the sample, the response will be directly related to the flow rate of the diluting gas. It follows, that for a mass sensitive device, the sensing volume can be extremely mall and, in fact, insignificant. However, for a device to sense a concentration change, the sensor must have a finite (albeit small) volume