Big contamination in GC-FID

[chemistab]

Hello,

I work on GC-FID with a Headspace autosampler (loop). The last 2 months i have a big problem with all the chromatograms. The peak shape is not good and also in chromatogram of diluent (DMSO, NMP etc) i take more than one peak.Maybe for someone it is not problem but the chromatogram is really awful.At the beginning the instrument blanks injections are good (without peaks) and when i make one injection of diluent (NMP or DMSO) the following instrument blank injection is not good.
First of all i thought that maybe there is problem with the column. I made a conditioning, i have also cut off the end of this and finally i bought a new one. The problem continued to exist. The next step was to change liner, some filters of GC and we clean FID. No good result. So maybe the problem is to the autosampler. The only i can do is to run a big number of instrument injections in very high temperature ( 250 oC with limit to be at 300 oC) to the transfer line, oven and the other parts of autosampler in order to clean autosampler. But i think the problem didn't solve.

I afraid that there is a big contamination somewhere to GC or FID or autosampler. I cannot think something more. Any idea maybe can help me. I really need it.

Thanks!!!!

[chromatographer1]

Replace the sample loop and replace the sample line.

I recommend a fused silica coated SS transfer line or a piece of fused silica tubing (blank FSOT). The rotor should be cleansed as well. Be sure to replace the sample loop with fused silica lined tubing.

If you are doing split injections then the injection liner in the GC is also an item to clean or replace.

best wishes,

Rod

[chemistab]

Thank you for your reply. How easy is to replace the loop and the transfer line? You think also that the problem is in autosampler?

[chromatographer1]

If you have the tubing and the fittings, it is quite easy. Loops may be purchased from the manufacturer or can be self prepared.

Transfer lines can require some time and effort. If fused silica lined tubing is used, flushing with a neutral or acidic solution will generally remove deposits without damaging the surface so that it would require replacing. Most lines are not FSOT steel or plain FS polyimide coated Tubes from the manufacturer, however.

Note: the non-volatile deposits left in transfer lines are not removed by heat. Rather, they are usually baked in ever harder, and more difficult to remove. Replacement is often easier than cleaning and more time productive.

I recommend that steel lines with an interior coating of fused silica be used. Alltech or Restek.

Good luck,

Rod

[EUROFINS]

You might also consider solvent (DMSO) purity, type of vial and injector septa and injection needle type and cleanniss.