Hi Romana i daily work with TSD detectors for pesticide analysis.
First check if the bead power is on. If yes look at the value of it. A new bead should have 2.8-3.2 Amps. Max bead power is 3,8 Amps. Can you see the bead burn when looking in the detector? If not check the detector gasses. First put the bead power off on the GC.
Then check the gasses over the detector. You need a flow meter for that. Check the Hydrogen flow by measuring it by putting off the air and make-up gas over the detector. The hydrogen flow should be 4-5.5 ml/min. Don't forget to add the column flow while measuring the hydrogen by attaching the flowmeter to the top of the detector. Then add the make-up gas to the detector it should add an extra flow of 25 ml/min. A total flow of 30-35 ml/min should result. At last add the (zero-)air. The air flow should be around 175 ml/min. So a total of ± 200 ml/min should result.
Put the bead power on and check if a signal of > 0.5 mV is seen. If not then increase the bead power with steps of 0.025 mv till a signal is obtained.
If no signal results then check the bead by turning the bead power off, cooling down the detector and visually check the bead for damage. The bead is located on the lower position of the detector. The upper position is the signal probe.
A greenish coloured bead or broken bead probably means that the beads needs to be replaced. If the bead burns and still look look ok (white crystal) then probably something else is going on (damaged signal probe, broken cable or board).
The lifetime of a bead is a few years depending how much it us used.
64 mv is rather high for a bead! A few mv is more then enough! The minimum is 0,5 mv. A higher voltage means a shorter lifetime and a quicker suppletion of the rubidium sulphate crystal. I work for 13 years with TSD's and the lifetime when a bead is on for 24/7 is about 2-3 years (signal ± 1-2 mv)!
Good luck!
Richard
Chemical contaminants Analist
