Radioactive tracers are currently used in a variety of industries and have the advantage that other than a small change in mass the tagged species is not chemically modified. Their primary disadvantages are the need to produce and handle radioactive material and the dangers of introducing radioactive isotopes into living organisms. This is a severe limitation in Pharmacology and Biochemistry. While radiochemical detection methods are normally considered highly sensitive, this is only true for off-line measurements where analysis time is not a limiting factor. In on-line measurements, as those made when analyzing chromatographic effluent, the detection time is limited to the width of the chromatographic peak and the detection limits are dramatically reduced.
Microwave power is supplied through a gold plated arm.
The cavity is tuned via two finely threaded pole pieces located on opposite ends of the cavity. The plasma occurs only inside of this tube since the remainder of the cavity is at atmospheric pressure. In the past, the plasma status has been monitored by opening the GC oven and viewing the plasma directly with the eye. The plasma color was indicative of the gas mixture. This has the disadvantages that the GC oven temperature is perturbed and the color evaluation is subjective.