Decreasing response from powders on GC-MS

Discussions about GC and other "gas phase" separation techniques.

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We're a fragrance manufacturer and we use GC-MS/FID to analyse fragrance samples. We run through a single column which it then split and goes through to two detectors - MS and FID. We dilute all samples 10% in acetone.

We're experiencing a rapid decline in response for powder materials in oil samples, eg. we see around 0.9% ethyl maltol in original sample, we add 0.7% to our physical sample and it responds as 0.08% on GC results, we then top it up to 2.7% in the physical sample, but it responds even less at 0.06% on GC results, suggesting it just isn't getting through to the detectors. The decline is visible on the FID and MS results.

We've never had this issue before and it is only happening with powder materials, which have been properly stirred and dissolved into the samples so the issue isn't here.

Any suggestions for solutions would be much appreciated, thanks
We routinely analyzed fragrances purchased for our consumer products such as soap, detergents, candles. We happened to dilute our incoming fragrances with methanol. We made an in-house GCMS library with thousands of components.

So "what" is this powder? If me, I would try to filter out the powder if I could. I think that the powder is depositing on the GC liner, building up over time.

How often do you change the liner, and how many injections are made per day?
Consumer Products Guy wrote:
So "what" is this powder? If me, I would try to filter out the powder if I could. I think that the powder is depositing on the GC liner, building up over time.

How often do you change the liner, and how many injections are made per day?


It's happening with most of our solid fragrance ingredients eg ethyl maltol, maltol, ethyl vanillin, coumarin, heliotropine etc. There would be no way of filtering out the powder as it's fully dissolved in the fragrance (as it should be) and also we wouldn't want to as they are key ingredients in the formula.

Basically we just need to get an accurate response of the amount of each ingredient in a fragrance, which we have been able to do for years, but lately the response of the powders has declined rapidly to a point where they're almost not there at all, even though we know there is upwards of 1% in there.

We check the liners every week and on average change them every month or so, and we do around 16 injections a day.
Is it the MS detector response that's decreasing? If so, it may be time for a new detector. They have a finite life, much to the dismay of pointy-haired bosses :lol:
"Have you tried explaining it to the rubber duck?"
I guess its probably worth starting from what we know...

From what you've said about the responses from both FID and MSD diminishing, the detector isn't likely to be the issue which is a good thing! The injector/liner seems to be fairly well cared for and replaced so its unlikely to be that alone but it does need testing.

Out of curiosity, have you reviewed your data over the past few months to see if there is a trend or is this something that has just suddenly happened out of the blue?

I would personally begin at the syringe... Could it be blocked? Might be worth checking to see if it actually dispenses in the way it should or is there a big lump of septum in there? A blocked syringe could lead to loss of response and is pretty simple and cheap to test and replace.

Move onto the injector. I'm presume that it's free of leaks and that the septum is in good condition. I'm guessing you're doing split injections, so we don't have to worry about the split vent not closing like you would for splitless, so I'm going to ignore that possibility and given the symptoms, the possibility of a clogged up split vent trap too.

Once we're sure that the injector is performing as it should I guess there's not a lot left other than the column and the splitter. Out of curiosity, what's your method? How old is the column and how is/was the resolution? Any tailing? Is it leak free and in decent condition and properly installed? Have you done all the usual stuff like column snipping and baking out/reconditioning? Have you checked that there is actually flow though the column using a liquid to check for bubbles actually coming out? If not that would certainly be a good start.

My guess is that its the most simple problem of all... The syringe. Fingers crossed its that as at least it'll be a cheap fix!

Good Luck

R
Not sure if this will be a helpful test but could be if you do not have this kind of data as the "only powder" aspect is interesting and puzzling. I would try preparing a solution of a problem component such as the ethyl maltol that includes a known amount of a liquid analyte that has a similar but non-interfering retention index - maybe ethyl octanoate assuming you are using a non-polar column - and seeing the ratio of recoveries.

The only thing that keeps coming to mind is that the powder just did not make it all the way into solution or is precipitating out somehow/somewhere post injection but you have that covered from your first post. Perhaps a small experiment like this could give a clue moving forward.
What is the temperature of the injection port/inlet?
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