Argon ionization detector operation

System (3) has been recommended for the separation and determination of 17,21-dihydroxy-20-oxosteroids, including cortisone [142], Prior to introduction into the GC system, treatment with sodium bismuthate in acetic acid at room temperature was performed, followed by addition of aqueous NaOH. The analytes were then extracted with chloroform. The column used was glass column (6 ft x 0.25inch), containing 3% QF-1 on GasChrom Q (100 to 120 mesh), operated at 225°C. Argon (150 mL/min) was used as the carrier gas, and detection was based on a P-ionization detector. It was reported that results obtained with a 1 1 mixture of cortisone and hydrocortisone were accurate to within approximately 1%. 

The development of the ionization detectors by Lovelock that evolved from the original argon detector culminated in the invention of the electron capture detector [2]. However, the electron capture detector operates on a different principle from that of the argon detector. A low energy 3-ray source is used in the sensor to produce electrons and ions. The first source to be used was tritium absorbed into a silver foil but, due to its relative instability at high temperatures, this was quickly replaced by the far more thermally stable Ni source. 

The connection to an appropriate detector flame ionization detector, thermal conductivity detector, flame photometric detector, nitrogen phosphorous detector (FID, TCD, FPD, NPD, etc.) is achieved via the four- or six-port valve being operated manually or electronically. The carrier gas (helium, nitrogen, argon, artificial air, etc.) flows via the valve only through the sampling column, at low flow rates (e.g., 25 cm /min) held constant during the experiments. 

The pulsed operation of the gas-filled detector illustrates the principles of basic radiation detection. Gases are used in radiation detectors since their ionized particles can travel more freely than those of a liquid or a solid. Typical gases used in detectors are argon and helium, although boron-triflouride is utilized when the detector is to be used to measure neutrons. Figure 5 shows a schematic diagram of a gas-filled chamber with a central electrode. 

System (2) has been described for the assay of corticosteroids (cortisone, hydrocortisone, prednisone, and prednisolone) in urine [141]. Prior to introduction into the GC system, the sample was eluted with 2 1 ethyl acetate-methanol, the extracts evaporated to dryness, and then oxidized with sodium bismuthate. Used in the method was a silanized column (132 cm X 5 mm) containing 2,2-dimethylpropane-l,3-diol adipate (0.65%) supported on celite, and operated at 230°C. The carrier gas was argon, and the detector used strontium 90-ionization. The standard deviation was 3.5 % (based on 47 determinations). 

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