POOR SEPERATION OF PERMANENT GASES

[chromgraph]

Sir,
SUB :- POOR SEPERATION OF PERMANENT GASES.
This is with response to my earlier posting dated 5th may 2005, I would like to give more details as mentioned by CHROMGRAPHER-1.We have a FISON TOGA System. Hydrogen and nitrogen are separating but only 20 % of the total amount. Remaining hydrocarbons are all separating very correctly and their peak areas are all agreeable .light gases and methane are separated in mol sieve 5 a column and hydrocarbons are separated in a porapak column and detected by FID.

Flow rate is maintaining @ 22 ml / minute in sample detector and 5 ml in reference detector of TCD. Carrier gas is Argon. I don't know what the optimum practical gas velocity of argon is. In their manual the have told to maintain a flow of 20 to 50 ml / minute. I tried at 28 ml at that time peak is still getting shorter as if it didn't get sufficient time to retain in the column. Also reduced the flow to 20 ml / minute and did the test but the out come was poor. Line pressures all maintaining properly.

Seeing the problem, I conditioned mol sieve column @ 300 degree and conducted the test. The same still encountred. What could be the problem? Is it the detector problem? But TCD base line is maintaining at 4000 to 7000 mv
Calibration gas (mixture of carbon dioxide, carbon monoxide, acetylene, ethane, hydrogen, proprane, ethylene, methane, nitrogen) with 0.9863, 0.4926, 0.2120, 0.276, 0.2062, 0.2023, 0.199, 0.1932 % and balance is nitrogen.

GC Conditions

Oven Temperature Programming
- Iso temp 40 degree iso time 10 mint
Rate 8 degree Iso temp 96 degree Iso time 0 mint
Rate 11 degree Iso temp 140 degree Iso time 9 mint

Rate 20 degree Iso temp 40 degree


Zone temperature 390 degrees

Time event
0 1800 sec
620 sec 1800 sec
300 sec 1800sec


TCD (det temperature 140 and fil temperature 250). Sample is injecting to the column via sample loop. Argon gas using is of chromatographic grade. And column pneumatic valves are rotary type.
Thanks
My email iD jnedunghat@hotmail.com
Company Mail: - Jeevan.Nedunghat@qewc.com (Capital J and Capital N)
Mobile: 57325912 (state of Qatar)

[chromatographer1]

Assuming your carrier gas is good, and I have my doubts about that, my guess is that your injection or trap switching valve is leaking and you need to replace and/or clean the valve rotor. It sounds as though your carrier gas is contaminated with air. Either a leak or the gas itself is not of good quality.

Did this problem arise or is it one you have had from the beginning? Again I repeat, this is important information you have not furnished. It helps to help the forum members help you by giving adequate information to assist us in diagnosing your problem.

I wish you good luck in finding your problem.

[arie2044]

Hi
first of all you don't tell the columns dimensions' it is very important.
check your carrier gas quality, and make sure there is no any iso-C4H10 in your standard, it ellutes just before H2.

[etiquette]

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