Chromatography Forum

Hi all,
Using a perkin elmer clarus 500, FID, trx-wax column and analysing MEK and toluene in paraffin wax and using argon as carrier.
i have a very unstable baseline that may vary up to 0.3 mv in milliseconds.
Please i need urgent help.
thanks.

It may comes from bad quality air, fuel or carrier. I already have seen such kind of bad baseline when some hydrocarbons were present in my air, fuel or carrier.
Make sure to use air and H2 generator correctly and HC's trap on carrier. If you don't have air and fuel generator, make sure to install appropriate HC's traps on your Air line, fuel line and carrier line.

You must start with this before to doupt something else.

Let me know if you need more details on this email instrumentseoul@gmail.com

I do have some HC's traps available if necessary that would be perfect for you.

chtamer,

How are you injecting this sample? Headspace where we can be more assured of the wax staying behind or direct where everything will land on the column. The baseline problem could be as simple as the wax slowly coming off the column, first up, then down in very broad waves.....

Best regards.

I am using head space injection, and i use HC trap on carrier line only, may this cause a problem? and what quality of carrier and hydrogen should i use?
thanks.

You need hydrocarbon (charcoal) traps on your carrier and fuel gasses and an oxygen and moisture trap on the carrier gas.

A very rapid instability such as you have is more likely to be electrical / electronics than gas. Clean the detector jet and its contacts, make sure that the detector body is firmly seated and that any cables to the electrometer are properly connected.

Whay are you using argon as carrier gas ?

Peter

Thanks Peter, i am using helium not argon..(mistake),
i do use HC and moisture trap for carrier but not oxygen traps, i do believe that it is electrical too but cant get to know the exact reason, do u have any more suggestions?

A few non-electrical tips -

Leak check with an electronic leak tester? A loose fitting or something could have contaminants hitting downstream of the trap.

Is your trap lying down (horizontal) or standing up (vertical)? If it's lying down, your gases could be flowing right over the sorbent and not coming in contact with enough of it.

Gas should be 99.9995% pure for best chromatography.

Diagnosing electronic and electircal faults is tricky unless you have specialist knowledge (which I do not have). If you have eliminated all loose connections (including where cables plug into boards and boards connect together) - NB to SWITCH OFF before you connect and disconnect things, then you nned to eliminate possible sources of external interference. Switch off or move as much as possible of all other electrical equipment around the GC, or drawing power from the same line. If switching one of these off makes the noise go away you have located the source, what you then do about it depends on what it is.

Good Luck

Peter