Organphosphate Flame Retardants in GC/MS

[Marvaz]

Hi everyone!

I am currently working in a project about organophosphate flame retardants and i have a problem that i would need your help.

Firstly we are using a 7890A GC connected to 5975C MS. Now we are in the stage of running our compounds in Scan mode to find the ions and the retention times of every compound and we are facing a problem with our chromatograms.
In the beginning we were using iso-octane as solution but the cromatograms had an alkyl pattern with many peaks (see foto), and we couldn't recognize the compounds peak. The instrument had installed a CI source and a DB-1 column. We tried many things (clean and change the ion source (install EI source), change the column (install DB-5), clean the detectors and the injector, try in different instrument) and finally we decided to change the solvent. So we made new stock of our compounds, but with toluene as a solvent, and the problem seemed solved. Actually you could still see those weird peaks but with lower abundance!
One day, unfortunately, without changing anything, the peaks are back with big abundance again! The next day the peaks are gone again, but after some runs they appear again! The worst thing is that there is not a standard pattern but it changes by itself, and with that problem we are not able to make a calibration curve! Has anyone anything to suggest or maybe a same experience? The problem maybe caused from the solvent?

I also upload a photo to make myself clear.

I don't know if that is important but by the time that the weird peaks appear the temperature is about 300 oC

Thank you in advance!
Marios

[Bigbear]

You might try methylene chloride as a solvent.
As to your problem I would first suspect an injection port issue. What are your injection port settings and volume injected.
Have you done any port maintence?

[Marvaz]

Thanks for the reply,

We don't think that the problem is in the injector because those specific peaks are not only appeared with both solvents but also in different instruments.
The injection port settings are injection temperature 300oC, the injection mode pulsed splitless and the volume injected is 1μL.

[Peter Apps]

Best guess is contamination of some surfaces that contact samples. Do the contaminants appear and disappear in series of injections from the same vial ?, or only when you are injecting form different vials.?

Peter

[Marvaz]

Hi Peter,

Yes the contaminants appear with higher abundance after 2-3 injections, but after we noticed that we started using different vial for every injection. Also in order to erase those contaminants, after every sample run we make a run only with the solution and every vial that we use are new ! That´s why we don´t have any idea and i asked your help!

Thanks for the reply,
Marios

[Peter Apps]

Hi Marios

Just so I am clear.

Do the contaminants appear when you do multiple injections from the same vial even though the first injection from that vial was clean ?

Do the contaminants appear when you inject fresh solution from a clean vial each time, even though the first injection in the series was clean ?

When you use a clean vial each time, are you putting a portion of the same solution into each different vial, or do you put a different solution into each vial ?

Have you confirmed with the MS that the contaminants are hydrocarbons ?

Try making a series of injections from vials with no septa.

Peter

[Steve Reimer]

The pattern could be septum material. Check (or change) your syringe, inject with no septum on your vial and check to see if you are leaving pieces of septum in your inlet liner.