digital output to PC radioactivity flow detector in GC



radioactivity in GC

proportional gas flow counter

nuclides H-3, C-14

external standardisation

ultra high sensitivity

Gas chromatography fractions labelled with H-3 and C-14 can only be detected in internal gas mixtures of the GCeluate with the counting gas by a proportional gas flow through counter. 

Modern capillary GC`s have quite a small eluate flow. The mixture of the radioactive sample vapour with the counting gas is quite difficult. Therefore, the vapour of the GC eluate has to be converted to a reproducible gas form in order to obtain stable chromatograms. raytest RAGA* offers 2 modes: Formation of CH4 under Hydrogen flow at high temperature and presence of a Platinum catalyst. This procedure is suitable for both H-3 as well as C-14. Alternatively, the formation of CO2 can be performed at high temperature over CuO2. This method is only suitable for measurements of C-14 because the H-3 would be absorbed by the drying agent before it can be counted. The condition of operation and reproducible results is indicated very sensitive by recording a plateau at the operation conditions. Therefore, raytest is automatically running a plateau at the selected operation condition with an external gamma source of Cs-137, which produces sufficient Compton electrons and indicates the present operation conditions. 

The single radiation events are digitally counted in a selected interval time. The digital result is converted into an analog output signal 0-1 V using a ratemeter. The ratemeter range, interval time, background subtraction, smoothing etc is displayed on a 4 line, 20 character LCD and selected, entered manually by a keyboard.

Auxiliary inputs of most GC-control and recording systems enable the input of 0-1V signal. Radioactivity can be recorded simultaneously with FID, TCD etc.

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