GC/MS column choice

[alexduan]

Hi, I have a organic carbamate precursor. I need to decompose it and analyse its decomposition byproduct using GC/MS. The possible outcomes are isopropene, CO2 and isopropylcyanate. When I talked to the lab staff, he needs to know the dimension of column, size, type. Anyone can help? I really appreciate. Or if you can suggest some references that I can read. I haven't used GC/MS before, so it's rather difficult for me to begin with no background knowledge. Thanks!
Alex

[krickos]

Hi

Did something similar some 4 years ago. Then I used a headspace injection on a poraplot Q 30m*0,32mm*10µm column. Started at a column temp of 30-35°C, scan from 33AMU to avoid air peak. Could detect CO2 and some other stuff up to isopropanol. A bit unsure on the isopropylcyanate if its suiteble for headspace injection (bp close to 110°C)but should work as acetonitrile and other higher boilers like 2-butanol usually does work fine.

Out of couriosity, how are you going to trap your more volatile possible outcomes (CO2 , isopropene?)

CO2 is a bit tricky sometimes, been up a few times in this forum (can stick to moist/rusty valv parts). If decomposition is made in a basic solution, CO2 might be lost (turned into carbonate ion in solution).

Intresting, keep us posted.

[AICMM]

alexduan,

0.32 Plots with MS are going to be challenging. See the post on fixed gases by MS.

On the other hand...... Do you have a lot of these components or trace levels? If a lot, you might be able to get away with a split at the MS to cut the flow to the MS down to the right amount for the MS but still maintain the right column flow. You would want to use a flow calculator to figure out a restrictor between the vent line and the MS.

Best regards.

[alexduan]

krickos and AICMM,
Thanks for your replies.

I have run my sample -aluminum diisopropylcarbamate in Shimadzu GCMS. (sorry, i don't have the model and column info with me now, will post tomorrow).

I dissolved my sample in DCM and injected into column. heated from 30 - 200 deg C that allowed it to decompose in the column. (unfortunately, i don't have a trap). the MS gave intensive and massive low mass peaks below 180 m/z (scan from 40 to 700 m/z). larger fragments were not seen. The MS expert suggests to dissolve my sample in acetnitrile then run on a MALDI MS.

I will keep you updated. Thanks again!

[Ron]

MALDI is an interesting choice for your sample, most MALDI matrices have a lot of low mass ions from the matrix, and it is not common to use the technique for molecular weights less than 200 dalton. There are heavier matrices available, but they tend to be less efficient at promoting ionization.