Tag: system

More Canisters!

Things are still going well and I have run a full set of my 11 canisters. The system is working well and I have done a little bit of fine tuninig in order to maximise the sensitivity for the compounds that I am interested in. These compounds, which correspond to my compounds detected in the snow samples (determined with SPME) are rather heavy (C2-C8).

I have, therefore, removed the water trap (cooled by dry ice) on the preconcentration system to avoid trapping my analytes there (this is less of a problem with more volatile compounds). I am using an HP-5 column, which is not sensitive to water as the previously used PLOT column for light hydrocarbons (which I would like to determine at a later date). I also heat out the liquid nitrogen trap under vacuum before proceeding to the next sample in order to avoid residues being stuck in the trap. Blank runs show that this is working well.

I also use 30% more sample for analysis than the people ususally using the system, because my peaks are quite small. The additional amount of sample and resulting increased sensitivity are much more reliable with an improved signal-to-noise ratio.

Canisters!

I started measurements of air samples, which I had collected in electropolished canisters at Alert. I use a home-built preconcentration system based on freezing out analytes with liquid nitrogen traps. Compounds are collected by freezing and flashheating the traps until they are collected on the column of a GC-FID (again using a cryofocuser) and separated.

A colleague gave me a crash course on how to use the system, which is a bit fragile (with regard to leaks), but has been working well so far. After familiarizing myself with the system, I ran standards in the last couple of days and I am now ready to tackle the canisters.

Running samples …

I have been running samples lately and things are looking good. Baseline of the GC-FID is solid at 2.7 pA for the instrument background. The only exception was this morning, when I had to fix a leak on the ultra-zero air cylinder (I wonder, where that came from?), which took a while to locate. But now things are working fine, although I am in for a long evening.

I use the same water that I have used at Alert for rinsing and cleaning (except that the feed is different – I have used DI water at Alert and I now use water from our standard MilliQ system as feed, because the pre-treated water is RO, which the cartridge in the portable system is not suitable for). Water quality is fine and blanks are very similar to those in Alert.

Today I run snow samples collected on June 2 at the Special Studies Trailer (SST), snow layers from 2-6 cm and 36-53 cm from the surface. I carry out headspace and liquid phase measurements in duplicates using a divinylbenzene-coated SPME fibre.