Chromatography Forum

hi all, i am currently using a headspace-SPME-GCMS for volatile analysis in oils. i finds that there are a lots of ghost peaks! i have checked with my GCMS system and is certainly not from my GC or MS. i have already conditioned the SPME fiber according to the instruction. the ghost peaks are mainly "silanol" etc silica containing components. do you guys have any idea?

These peaks are likely to be from a source of silanes in the instrument, which could be the column, the septum, or from the SPME fiber if you are using a silane phase.

If these are from the column, 1) take the normal steps to avoid causing column bleed - posted many other places. 2) Because all columns bleed anyhow, if the instrument has sat a while, allowing degredation products to accumulate in the instrument, run through a temperture program (no injection) to the upper temperature you intend to use in your analysis. Hold for a few minutes and then run your sample.

For silanes from the septurm: 1) confirm that the septum purge flow is working properly. 2) be sure that you perform inlet maintance on a regular basis. In this case you want to be sure that bottom of the inlet is clear of crumbs that fall from the septum as the syringe or SPME sampling device penetrate the septum repeatedly.

For the fiber: This is not the first place I tend to look for a source of siloxanes - because there is not much stationary phase present on the fiber. Do not overheat the fiber and be careful to avoid conditions that will start degredation of the stationary phase. The same things that cause a column to bleed will cause the fiber to bleed. And, expect to replace fibers ocasionaly. For headspace applications, this may be many injections between replacements. For other applications you may have the fiber survive relatively few injections.