Chromatography Forum

Hi All,

Since we are still fairly new to Gas Chromatography, we were discussing about sample preparations. then it kinda occur to us for HPLC, filtering the sample with 0.45 micron membrane filters is a necessary step to avoid damaging the system. since we now have a GCMS we were wondering whether is it realy necessary to use 0.45micron filter or would simple filtration with filter paper be sufficient.

my argument against using the membrane filter was that we are using deactivated glass wool in our split/splitless injector and the injection volume is only 1 microliter. so any fine dust would simply just gets trapped in there since all of the samples would be vaporize anyway.

Particulate muck in any sample is likely to be a problem, in GC the main issues are likely to be blocked or jammed syringes, and involatile residues in the inlet. That said, a sample that looks clean is probably OK for GC without filtering. Bear in mind that filtering can add contaminants.

Peter

I agree. As long as you cannot visually see any particulates in the sample, consider it clean enough to run. Keep sample prep as simple as you can.

I will confess to even running GC samples that were slighly hazy. And I will only say that I got away with it. I can not reccomend it. But, if you have to -- A syringe is a consumable and can be part of the cost of an analysis!

If you have some visible particles, you might try centrifuging the sample. We have analyzed hundreds of charcoal extracts (from air sampling tubes) after simple centrifuging 15 min @ 3500 rpm and transferring some clear solution to insert, and had no problem. No syringe blocking, and any residual tiny particles (minute amounts) were trapped onto glass wool in the liner.

If you really need filtering, find some very inert filters, so that your solvent won't extract any impurities. And run a few blanks (filtered solvent)!

Filter paper might be OK (try running a blank), but you have to use some lint-free variant, otherwise your sample might end up with more particles than before filtering!

I was always afraid of introducing contaminates using filters, so I would centrifuge. Then I ran a sample where the active and solvents were different phases and centrifuging caused assay values to drop to near nothing. Now I just shoot samples "as is" and replace syringes and liners more often. (More often being about once a year, and before that we never replaced them.) Yeah, no one here is a GC sage; we just learn as we break.

Thanks everyone for the input it really help us out alot,

so to sum it, for Gas Chromatography the sample should be clear and doesn't really require the same 0.45 micro membrane filtration like HPLC does.

and centrifugation is prefer over filtration.

Tarapan

Gross samples with a high split ratio can also very quickly clog the split vent line and trap, causing weird pressure fluctuations. Particulates getting stuck on the liner and gold seal also provide nice active sites if your sample is particularly reactive.