Chromatography Forum

Hi,
Please explain me what is the best way to regenerate a molecular sieve 5A. I normally use Helium or Argon as carrier gas.

I problem I met is that I lost the O2 peak in low ppb concentration. Is there something special to do in the column regeneration process.

thank you

If your peak has suddenly disappeared, check to make certain that your detector still has good sensistivity for other trace gases, and the correct sampling loop size with flows working OK.

Conditioning depends on the column maximum operating temperature, and whether any other columns are in the oven. For PLOT fused silcia columns, they usually have a maximum of about 190C.

I prefer to condition a plot column overnight at 190C with helium, but the really important aspect is to make sure that you maintain at least a low flow continuously after conditioning. If you have a packed column in stainless steel you can go up to 265C, but you should follow the manufacturer's recommendations.

The other aspect is to ensure that your carrier gas purifiers are all functioning correctly, and the carrier gas is pure. Make certain all your detector makeup and reference gases are also pure.

Bruce Hamilton

I have a home made GC I use for packaging gas two parallel columns Haysept the other MS5a the columns go to different sides of a TCD detector pair. Responses go up and below base line.
When MS5a column is getting near regeneration the oxygen and nitrogen peaks shift towards the injection point the dont decrease in size.
I suspect that you are looking at a detector problem or a loss of sample at the injection point.

Bob M.

The best thing to do if you lose your oxygen peak (which is a common problem actually) is to use air or oxygen to activate your sieve.

Activate slowly up to 250 °C and hold for 4 to 24 hours (experiment to find out how much activation you require).

0.125 in columns use 20-50 mL per min. 0.0625 inch column use 5 to 20 mL per min.

Rodney George
Senior Research and Development Scientist
Supelco