Chromatography Forum

Hi.

Obtain info from Agilent that a 0.53 & 0.32 mm i.d. column, 30 metre cannot be used in GC-MS. Is it true and may I know what is the reason?

Thanks

hi,
0.53mm column definetly won't work but 0.32mm will.
we are using 30M hp5 of 0.32mm dia 0.25µm thickness. no issues.
in mega bore column connected to high vaccum system you will not get resolution.
the best is low dia low film thickness.
good luck
vijay
india

I agree with Vijay and I am wondering why you want to use a megabore column (high load) to use in a quite sensitivity (low load) analysis method.

Anyway, being creative, you can obviously use it with a splitter before the MS interface, that will decrease flow and sample into the MS.

I used this technique in the past, when systems where not developed as they are today and also for LC-FABMS.

For Agilent MSD, the flow into the MS part is typically <2ml/min. However, the mega bore column typically has flow rate >3 ml/min. That is why 0.53 id column can not be used unless you use the splitter. But what I was told that the splitter is actually not a very good choice......

One example of when this is commonly done is for volatiles analysis: when a purge and trap system is connected to a GC/MS. You need a high flow rate to efficiently desorb the trap: hence the megabore column. But, of course, you can only tolerate a low flow rate into the mass spec.

We used to run a 0.53 mm column, but we had to use a jet separator interface with the mass spec. With volatiles, the jet separator cuts the sensitivity somewhat (roughly a factor of 2). With larger molecular weight analytes, this probably would not be much of a concern.

You can use Megabore columns with a GC/MS provided it has enough pumping capacity. Usually 250l/s turbo systems only. Most do not because the high pumping capacity will suck carrier from the end of the column changing the chromatography from that obtained with other detectors. There is no benefit to running Megabore and it does strain even the large turbos so not advised. I do however remember some fast GC papers (Thermo Finnigan Masslab) that looked at using a restriction 100um ? pre column and a short Megabore column to produce GC in a partial vacuum leading to very fast peaks. I think this was dropped thanks to fast heating GC systems (Trace 2000) and the Trace Ultra

As suggested you can couple Megabore column with a 0.25 mm ID fused deactivated silica tubing (may be of 2 meters in length) using coupler and then it is easier to connect to GCMS, I have used this and works very fine with CLARUS GCMS from perkinelmer. This is more useful when you have to detect OVI or residual solvents using Headspace and using 624 megabore column

Along with pumping capacity is the difficulty (or extra effort) in obtaining stable very low pressures at the column head (to keep the flow low). Typical maximum MS flows are up to 1 to 2 ml/minute (up to about 4 on high capacity turbo on Agilent). Low diameter transfer column may be needed to get correct velocity into detector.

As per earlier replies, megabore not practical - why would you want to use it? However, crude results have been obtained on commericial instruments for an application.