Liquid Chromatography Detectors - Transport Detectors > The Modified Moving Wire Detector > Page 69

 

Compton and Purdy (39) redesigned the Pye Unicam FID by inserting a rubidium silicate glass bead above the flame and thus made its response  specific and changed it into a nitrogen phosphorus detector. Stolyhwo et al. [40] employed metal spirals wound on wire and stranded wire to increase the surface area of the carrier to increase the proportion of the column eluent taken into the detector. A detectable mass of 100 ng of triolei was claimed but the actual concentration sensitivity was not reported. Pretorious and Van Rensburg (41) tried to increase the carrier take-up by coating the wire with sodium silicate, kaolin and copper kaolin. some improvement to appears to have been realized. Slais and Krejei (42) replaced the normal FID with the NPD detector and used it to detect chlorine compounds. They mixed the combustion gases with hydrogen and passed the mixture directly into the NPD. At a column flow rate of 0.37 ml/min., the sensitivity of the detector was stated to be about 3 x 10-7 g/sec, which is equivalent, in concentration units, to about 1.6 x 10-6 g/ml.

The moving wire detector has also been modified by Dugger (43) for radioactivity detection (e.g., detection of 14carbon labeled compounds). To detect 14carbon compounds, the solute on the wire was oxidized to carbon dioxide and the radioactive gas passed to a Geiger-Muller tube. To detect tritium, the tritiated water produced on combustion was passed over heated iron to reduce it to hydrogen and tritium, which was then also passed to a Geiger-Muller tube.