Diminishing peak area...

[CLabs]

Howdy all. I have been struggling with my SRI 8610c gc and I can't tell you how glad I am to have found this terriffic forum.

Anyway, we here at my lab have a large problem. Allow me to preface this by stating that we are using an SRI 8610c gas chromatograph, a hydrogen carrier (our tank has adequate pressure and gas in it), an FID, and a restek MXT-5 capillary column. Things have been running great for the past few months but like all things, this has changed.

Ok so... The area beneath our peaks have dimished greatly within the past day or so and are now reporting values that are a mere fraction of the known values within our check standards. We have always ran things at 250 degrees celcius and nothing has changed over the past few months. To troubleshoot, we have cleaned the FID, swapped out the old cappilary column for a new one, cut the column at both the injection and detector ends, tested for leaks, replaced ferules, adjusted running temperatures (from 240 all the way to 275), and cleaned out just about every part we were able to remove. Now I am at a loss. Our peak height used to report values of around 13-14% (that's weight %) and now are somewhere around 0.3%.

Now, my question to you, my fellow chromatography enthusiasts, why would this be? Like a said, our gas is at a healthy and functioning level and our machine has been running strong for the past 2 or 3 months (as long as I've been workinng at this laboratory). I'm left scratching my head and I am reluctant to contact SRI (tech support is time consuming and I am very busy at the moment)... so...

Any help you can offer me is greatly appreciated. Thank you very much!

[CLabs]

Oh and I am a newbie. So please take it easy on me if I ask some very obvious follow up questions

[chromatographer1]

Trouble shooting is a process.

Is the detector as sensitive as it once was to a known mixture which should part of the certification process.

No?

Then is the test sample getting to the detector? Check splitter ratio, column flow rate, injection size.

Or is it not burning properly to a maladjusted flame? Or an electronics problem?

Is the electronics - computer settings are the prescribed settings?

One step at a time.

Rod

[CLabs]

Trouble shooting is a process.

Is the detector as sensitive as it once was to a known mixture which should part of the certification process.

No?

Then is the test sample getting to the detector? Check splitter ratio, column flow rate, injection size.

Or is it not burning properly to a maladjusted flame? Or an electronics problem?

Is the electronics - computer settings are the prescribed settings?

One step at a time.

Rod

Rod,

Thank you very much for your repsonse, I really appreciate you taking time out of your day to help me address these increasingly pressing issues.

To answer your questions, I would say no, I suppose the detector is not as sensitive as it once was.

The sample is getting to the detector because chromatography is still occurring (albeit in a diminished form) and the air leaving the detector produces steam (an indication that the chemical reaction that turns oxygen and hydrogen gasses into water vapor is still happening). We do not have a split column, the flow rate has remained unchanged (I checked it this morning), and since it's a hand injected GC, operated by yours truly, I can assure you that the injection volume has not changed.

When we cleaned the FID everything appeared normal afterwards and the FID was reassembled the same way it was disassembled... is there some way I can check to see if its burning improperly? And the electronics are all functioning, as far as my eye can tell. All exhaust fans, lights, heating elements, and the detector seem to be doing just fine.

The computer settings have not been altered (except for the experimental temperatures I set and later returned to normal)...

And yes, one step at a time. One step at a time. Thank you good sir.

Please let me know if there is anything else I can provide you with that might give you a clearer idea of the problem I've encountered.

[chromatographer1]

The state of physics at the present time indicates that something has changed.

You may have a leaking septum.

You may have a cracked column or one leaking at a fitting or ferrule.

Do you have a flow controller or a pressure controller?

If the latter then you could have a leak at the head of the column.

If the former then you could have a leak at the tail of the column.

You may have a leaking syringe, losing sample around the plunger.

You should, if you have not already, checked to see if your gases are correct in type and purity, that your traps are good.

Is your signal normal but low response, or noisy or having a high auto zero offset?

Did this happen slowly over time, or over a day or two at most?

best wishes,

Rod

[Johnny Rod]

What's the sample and how are you injecting it?