Carrier gas impurities?

...By washing the Electrin Capture detector (accordin the instruction), deoxo/moisture purification of the carrier and make-up gases, and long-term conditioning the column.

Hi, We use an ecd on a Varian 3800 instrument and to make it less noisy and to keep it «clean» I increased the make-up gas by 10cc/min. I loose a bit in sensitivity but my background stays low. I have to mention that I do environmental samples that are quite dirty so I prefer a little loss there. Maybe you can bake out at a higher make-up gas flow and watch how is evolves. It should go higher in signal and then come down after an equilibrium. Make sure your make-up is clean add traps to filter the gas, good luck, P

I don't have traps on the carrier gas line. I've never needed them in the past. Is it possible the UHP helium isn't clean enough?

Do you have another detector you can test that carrier gas with? That would be the easiest/cheapest test you could do before you try anything else.

The impurities in the carrier gas and make-up gas, and/or contamination of detector head, are the main causes for high background of ECD. The use of unconditioned column can contaminate the detector.  Conditioning of a new column should be done disconnected from the ECD, and use of deoxo- and moisture traps on the gas lines is obligatory.

Regards!

Dear colleague, you should have:

1- all gas pipes are metal, copper or steel,

2- gas cylinder equipped with double step high purity pressure regulator with steel membrane ,

3- high purity N2 or Ar+5%CH4 (99,9999) as a additional gas (in capillary column as carrier gas He 1ml/min))

4- flow of additional gas 40-60 ml/min, detector temperature 250C

I hope these suggestions help to obtain lower detector frequency i.e. less then 1KHz.

Best regards I.Sliwka.

Be aware of subtle air diffusion (O2 isn't tolerated by ECD) at the injector block. Is septum purge flow high enough to avoid air retro-diffusion? Are alle the connections airtigh? Water adsorption may contribute to high background. Bake at 300°C under flow for at least half an hour. As last resort, inject some hundred microliters of very pure liquid water inside the ECD (from the exit side towards the interior of the ECD body)  while it is very hot and under carrier flow (vapor cleaning method: Have you heard of it?). [email protected]

You increase baking  time for ECD detector at high temperarutre.  Second thing you purge the column with carrier gas. It may reduce the GC-ECD background.