Chromatography Forum

Hi,

I am analyzing organochlorinated pesticides on GC-ECD 5890 series II dual column configuration. This machine has been run constantly over the past 5 years. I am noticing that a few parameters are getting low in area on both columns compared to my other 5890 instruments particularly hexachlorocyclopentadiene. I have tried new liners, changed the inlet body, changed the columns (DB-5 and DB-17) and nothing seems to work. When I calibrate the internal response is fine, even the lowest standard at 2ppb. It just worries me that the area is so low compared to the other compounds.

I was just wondering if anyone else has come across this problem.

I also would like to know if tightening the column nut too much can effect this. I have to ove rtighten to get a reproducible internal standard area. I do maintenance every other day and the areas always vary. Is this normal?

Thanks in advance for the help
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How old is the standard and is it UV protected?

My standards are not old and they are kept in a freezer. My other instruments do not exhibit this response and I use the same standards.

dalarie,

Wool or no wool?

Have you thought about changing inlets or even just the plumbing to the current inlet. 5890's will collect crap in the split line and septum purge line that can haunt you.

Best regards,

AICMM

I don't use wool. I am going to change the chemical trap this week. I also ordered a liner with wool to try. I am wondering if it is worth to just condition the trap in the oven or should I just purchase a new one? I don't think the trap has been changed in the past 5 years anyway.

Does glass wool help?

Thanks for your reply.

dalarie,

Wool sometimes helps the evaporation of analytes and thus their response. It can also be a source of active sites and thus eat your compounds of interest. If you use wool for pesticides (I would) then I suggest only the slightest amount.

Regarding the inlet, I would suggest you rinse the lines to and from the inlet with methanol and hexane. Often these will be gummed up after years of use and can cause active compound issues.

Best regards,

AICMM