Chromatography Forum

I should tell u that i just started working at the forensic lab 3 weeks ago and im still new to this.
The formation of formaldehyd was an assumption. But its our best bet, as formaldehyd is highly reactive
However here are the mass specs:

First Methamfetamine (and its mass spec) and then the "smear" followed by the peak we cant identify.




And here is the mass spec of the unidentified peak. The "smear" has almost the same mass spec as the unindentified peak.
We assume that the high peak at 108.1 is the ring structure that has reacted with formaldehyd (or at least that my best bet) however it could be anything. It was this peak that lead me to the idea that formaldehyd might be reacting with fragments.



Im still very new at this and this was the first problem i was presented with
Any help is greatly appriciated

BOW DOWN TO MY AWSOME PAINT SKILLS

Whatever the mystery compound is, it is not the benzyl alcohol that you show:

http://webbook.nist.gov/cgi/cbook.cgi?I ... #Mass-Spec.

A smear between two peaks that might be interconverting is often a symptom of the conversion happening on the column rather than in the inlet. Have you tried a new column ? (you might have mentioned this early on - the scroll back does not go far enough).

Peter

Yes we have tried a new collum, also one without the duraguard (10m inactive collum)

I thought the benzylakohol might be the single peak at 108, not the whole spektrum.

The whole spektrum is the mystery compound.

I thought the precense of benzylalkohol might strenghten the assumption the formaldehyd was present and was reacting with the fragments of methamphetamine.

We are still testing the inlet for leaks, and we might have found some indication that there is a leak.
However we will do futher testing after the weekend.
Still, feedback is welcome

It's Friday. I know where I would go next but it would mean that I am going to work this weekend. I am also comfortable
doing the work so I would not hesitate. I would seal up the column on the Good GC/MS (piece of septum) and take the
inlet out and swap it for the "bad inlet" on the dead GC/MS. Divide and conquer. Of course my problem would go away and
I would look liked a genius.... Or not. But at least you are not still chasing a problem that isn't really the problem.
As a former supervisor once told me, "If the GC is not running we are not making money!" The risk is.... you take down the good to
troubleshoot the bad.

Best regards,

AICMM

Stepping back a few posts. You say that you inject the same sample on the next GC and do not see the extra peak. Are you using the same column, liner, temperatures and other conditions, including detector.

What happens when you shoot a sample that is just methanol? And a standard made in methanol?

Stepping back a few posts. You say that you inject the same sample on the next GC and do not see the extra peak. Are you using the same column, liner, temperatures and other conditions, including detector.

What happens when you shoot a sample that is just methanol? And a standard made in methanol?

The other GC is IDENTICAL in every way.
Alle standards are made en methanol.

We have not injected pure methanol.
There is a solvent delay system to increase the life of the filaments.
We can overwrite it, but my superviser is not happy about it.
But i think ill do it today, just to see if formaldehyd is formed.

Updates will proberbly come later today or tomorrow.

Have you tried to add 100-1000 ppm of formaldehyde to see what happens?
it will not solve the problem but at least you will be able to confirm your hypothesis.

We found a leak and are now running out test solution again...

If this doesnt work, we will make a new test solution with ethanol and add formaldehyd to see if our hypotesis is correct...

We found a leak and are now running out test solution again...
If this doesnt work, we will make a new test solution with ethanol and add formaldehyd to see if our hypotesis is correct...

Remember, some formulas of denatured ethanol also contain up to 5% methanol...

We stopped the leak and the oxygen dropped.
However it didnt solve the problem.

We have access to pure ethanol.
So tomorrow well try to add some formaldehyd.

If there was enough oxygen in the carrier gas to react with the methanol solvent I fear that the column might be bady damaged, and that is the cause of the peak distortion.

Where exactly was the leak ?

Peter

With a mass spectrometer - you will always see some oxygen. There is always a small leak through the seals of the mass spectrometer. An additional source of air entry into at GC/MS system can be the split/splitless inlet. If your head pressure is low enough, air will diffuse into the inlet if the split vent is open. This can be decreased by increasing the split flow. And you can have air enter through the septum purge and through a cored septum.

You should see some air background on the other GC system. How does it compare when you run the leak check on that instrument?

The reason I suggested injecting methanol was to eliminate reaction of anything but methanol from the picture. If the contaminant peak is still there, it has nothing to do with analytes or other contaminants. If the strange peak is still there, the next step is to push the run button on the GC as if making a manual injection. This will eliminate anything coming in through a syringe or in the solvent.

If you look in methanol for formaldehyde, you will find some. If you check the specifications on your methanol, you will most likely find that it is certified to contain less than some level of formaldehyde. And that specification is good on the date when the methanol was analyzed. If your methanol has been sitting in a stockroom for a couple of years, the level of formaldehyde can increase. Also expect to see some formic acid and methyl formate.

If the methanol has been stored in a clear glass bottle in the lab, look for these to grow even more.

If there was enough oxygen in the carrier gas to react with the methanol solvent I fear that the column might be bady damaged, and that is the cause of the peak distortion.

Where exactly was the leak ?

Peter

At the helium intake.
The oxygen er is 2.1% which is normal on this GC