Hello,

The column may have been worn out.

If a guard column is installed in front of the analytical column, check the peak shape after removing the guard column.

If the peaks return to normal, the problem is with the guard column.

That seems a chromatographic problem, not a fiber-related one. The weird "shoulder" is most probably due to split valve opening/fiber retraction. Red peaks areas are much larger, are you sure you're using the same settings? Seems like the blue are acquired with a split injection and the red with a splitless one. In such cases, it's necessary to share as much details as possible about the analytical setup, if you're searching for a sensible answer.

Sorry Salvatore, but I think it is not a chromatographic or column problem because the chromatographic conditions and the column are the same. It's an SPME fiber problem. The performance of these varies between lots of the same producer and also among lots from a different producer. In other words, if we acquire fibers from the same supplier we can observe some variations between the different fibers (with the same coating). These variations are related to the packaging performance of the material that can vary from batch to batch and to the slightly different size between particles. If you purchase SPME fibers from 2 different producers you may even have significant differences between your performance. It's a matter of luck with the material lot. Supelco's have always been the best, in my opinion.

Regards

JSCamara

Thanks for all your responses! The exact same GCMS conditions are being used on the same sample. Equilibration, trapping and desorption conditions are also the same. I agree that it probably is a fiber issue, but am not sure what the problem is or how to fix it. I have tried reconditioning the faulty fiber but it didn't change anything.

Here are my analytical conditions:

Column: DB-Wax (fairly new column)

Equilibration 20min, trapping 30min

Desorption: splitless mode, 240C, 1min

I agree with Salvatore and Yasin; if the peak shape is the issue then it has to do with the GC-column or GC conditions. If the peak area is the problem then also the fiber can be the cause. The 'quality ' of the fiber can not have this clear effect on the peak shape. Check with new column or new fiber to find the cause.

But the GC conditions are the same with the same capillary column -

in one chromatographic run you have gaussian (narrow) peaks with exactly the same conditions in the next ruin you have wide peaks (tailling). It cannot be from the instrument. If the SPME fiber was the same, I would say that might be problably loss of extractive efficiency due use (depending on the nature of the matrix they can be used 100-120 times in headsapece mode) but as the fiber is another (it is the only variable in the process) it is the fiber performance which may vary from batch to batch. Another parameter that can be important is the septum in the GC injection port - if the septum has already been used a lot it can widen a little and cause this type of problem. So changing the septum may be another hypothesis to solve the problem, or try another fiber (thirth).

Rehards

JSCamara

José Câmara, I am still convinced that it is a chromatographic problem. I tend to exclude a septum problem as retention times are not affected and peak areas increased. Fibers quality obviously varies from lot to lot (even if I never encountered such differences). A test with a third fiber is clearly necessary (from a different lot, if possible). In my experience, split injections are usually better than splitless for SPME, but, again, we miss fundamental analytical data: analytes, instrument, column data (DB-Wax ID, length, flow....), temperature program, liner type and so on. Chromatographic problems are often coming from neglected details

I believe that you r getting different peak shapes but same peak area counts in both chromatograms. I feel these are real practical issues that researchers encounter and hard to trace the reason quickly. Sometimes due to very sensitive issues like "worker's skill" in manual injection. I can’t say the exact reason here but can propose few things to do.

1. Inject Silylating agent and condition the column. Check the liners and septum, if not clean enough, replace them. Then try again.

2. Use “pulse-split” or “pulse-splitless modes” and see the result.

Hope you will able to fix the issue soon and let us know how you have done it.

Cheers,

If you prepared and inject the samples consecutively, I mean if the GC analytical conditions are not a variable parameter in terms of day-to-day reproducibility, it is nearly certain that the problem is coming from SPME coating. It seems that the adsorption affinity of the coating is convenient for your target analytes but the elution profiles are indicating that secondary interactions exist between molecules and fiber coating thereby diffusion of the targets was shifted and band broadening along with tailing arisen. This is a typical issue for GC columns but we conduct similar interaction and elution patterns at SPME applications therefore irreproducible fiber coating sourced problem can also come to mind.

I might have missed this somewhere but are the two SPME fibers run on the same day or are you overlaying the new results onto the previous? If the former is true, toss the new SPME fiber. If the latter is true your problem is most likely your column. Clip the column. We have never experienced batch to batch variability for SPME fibers but we experienced it with SPE cartridges.

The SPME fiber is the only variable between the two consecutive runs. Reconditioning the "faulty" fiber and GC inlet maintenance haven't helped with the peak shape. I am certain it is a fiber problem as I have been able to replicate the same results again. The fiber with the perfect gaussian peak shape has been used for around 200 injections, whereas the faulty peak shape fiber is very new. I think İsmail Emir Akyildiz you're right that it may be a diffusion problem, but I don't know how to fix that. Does repeated use of SPME fibers improve diffusion?

The unreacted surfaces on SPME fiber should be deactivated even if the conditioning steps are not helpful. Increasing the inlet temperature for a couple of injections may be beneficial considering the upper-temperature limit of the SPME ligand. Fiber coating is a hard process and Scanning electron micrograph can only validate the coating is uniform. Unreacted silica resulting silanols may shift the molecule diffusion due to secondary unwanted interaction undergoing hydrogen bonding. Try to deactivate the silanol residue and ask the vendor for SEM images, alternative conditioning steps, or as a complete solution request the product replacement if you did not observe a similar situation at your comparing SPME at initial usage.

Since you are using the WAX column, retention at PEG material indicates your analytes have an affinity of hydrogen bonding and unreacted leaking silica is a good option for your molecules.