Hi Carol
If you are going the urea + urease = ammonia route then I would use wet chemistry to measure the ammonia - at best it is going to be tricky by GC, and at worse a bit of ammonia and a bit of moisture will mean goodbye column in fairly short order.
Hi AICMM
I was using a very thin film methyl silicone (0.1 um, 250 um, 30 m from Restek). What astonished me is that these two molecules, which are bristling with active sites, even made it through the column. Plainly the column is very well deactivated ! Detection was by MS. When I tried the same sample with a wax column there was no sign of either compound - they are probably both still in there somewhere
Peter