Phthalates tailling GCMS

[Teodor Costache]

Hello,

I am having a problem regarding phthalate analysis on a Thermo Focus/Polaris Q ion trap. Last week the chromatography suddenly got really bad, with the peaks showing tailling and reduced sensitivity. I can't figure why this happened, the only dirty samples I injected before this started happening were some headspace VOC's. These were indeed dirty samples, but I thought that headspace analysis doesn't impact the system - only the volatiles are injected.

Anyway, I changed the liner and cleaned the inlet, injected five blanks and then a standard mix at 0.5 ppm. The first standard mix chromatogram looked really good (even if there are some extra peaks - wich can be expected for the first injection after maintenance), but then the peaks started tailling again.
This is an image with three consecutive injection of the same standard:


This is the chromatogram of 0.5 ppm injected on 22.05.2014:


The sample is injected in splitless mode, 1 microliter injection. Injector temperature: 250 C. Solvent: hexane
Oven program: 90 C / 2 min, then 20 C to 275 C for 18 minutes.
The column is inserted in a Thermo Swap it transfer line wich is kept at 310 C. Ion source temp: 250 C.

From the fact that cleaning the injector resulted in a single run improvement, am I right to assume that the problem is with the injector? Does anybody have some advice?

Thanks,
Teodor

[Teodor Costache]

Forgot to add: The colummn is a Thermo TG 5MS, 60m x 0,25 mm x 0,25 um fitted with a 3 m GuardGOLD 0,53 mm by glass union. The flowrate is 1 ml/min.
The splitless time for the inlet is 1 min.

[Peter Apps]

If I am reading the scales in the chromatograms correctly then the tailed peaks are actually taller than the sharp ones, and consequently have much bigger areas.

The only thing that I can think of that would cause this is a split valve that is stuck closed so that you have a permanent splitless injection.

Peter

[Teodor Costache]

Nope, the tailed peaks have a smaller area than the tall ones. The first chromatogram also contains additional peaks (ghost peaks), and so the rest of the peaks are normalized to the tallest peak - in this case one of the ghost peaks.

The peak areas are displayed on the chromatogram with the label AA. My standard mix is composed of six phthalates - the only peaks present in chromatograms two and three.

[carlo.annaratone]

Does the tailing happen with other analytes as well? If changing the liner did not do the job, I would think of a particle stuck at the head of the column, or something that contaminated the source and causes asdorption on the metal

[Teodor Costache]

I haven't tried other analytes, I think I will inject a organochlrine pesticides standard to see how they look.

I'm leaning to think that the inlet is to blame. But what baffles me is that this is the first time I have seen a cleaning restauring performance for one run, and then declining performance again.

[Peter Apps]

Check the septum for tears, and the needle tip for sharp edges. With a damaged needle tip it only takes one injection to dump a piece of rubber into the liner, and non-polar compounds like phthallates just love rubber.

Peter

[Teodor Costache]

I switched the liner again, this time with a new one. The replacement liner that I used earlier was an old one that we washed with several solvents - we don't have a silylating agent, yet. After I installed the new liner, peak shape was as sharp as can be, and tailling didn't start to occur again like with the reconditioned liner.

I guess we will have to start using silylation, as throwing away so many old liners is uneconomical. Thank you for your help.
Teodor

[Peter Apps]

Phthallates are quite tractable compounds, and I doubt that the tailing was dues to interactions with silanols in the inlet, so I would be surprised in silylation would make much difference. The main requirement is to thoroughly clean the liner - general dirt gives non-specific ab/adsorption of compounds like phthallates.

Peter