MXT Biodiesel Column on MS

[abharga3]

Hello everyone

I have a Shimadzu GCMS-QP2010 equipped with both MS and FID. I was using the MXT biodiesel column (15m, 0.32mm ID and 0.10um df) on it, with the FID for the last six months. I recently decided to switch it to MS for a proper identification of my product species. Since I am new to the 'chromatography business' I seeked advice from labmates who had previously used the MS. They advised me to use the same method file for the MS too and that the retention times would shift a little because we scored the column a little bit and because its a different kind of detector altogether.

I run the samples but all the peaks clubbed into one huge trailing peak. I had previously used the petrocol column from sigma aldrich( 100m x 0.25mm ID, 0.5µm film) and from that method I found a huge difference in the column flow of the carrier gas (helium, 3.81ml/sec to 1.82ml/sec). When I tried to reduce the column flow for this column I always got a negative pressure at the inlet? I tried using the isothermal run as well (80C) for 200 mins but the substances always eluted together. One thing I have observed is that the vacuum pressure has been around 8.9kPa all the while, which in the petrocol column used to be really low. Is it because of the short column length that it is not able to generate a vacuum in the MS? A stupid thought that came up was is the MXT biodiesel even suitable for GCMS application?

Any suggestions would really help me out.

Thanks

[Peter Apps]

Your suspicions are correct - the column is too short (or too wide) to be connected directly to an MS. A piece of narrow bore (50 um) deactivated silica tube connected with a press-tight connector could be used as a resistor to reduce the flow, but it will need some tweaking and method adjustments to get it working nicely.

Peter