Chromatography Forum

Hi,

I am looking for a way to analyze for urea in solid samples using GC. I think there is a derivatization method but haven't found the info yet. Does anybody out there have some experience with this compound?

Thanks.

Carol

cmoral,

I have not worked with urea. By it's ionization potential it should be measurable by argon ionization detector or by photoionization detector but it will be difficult to chromatograph. If you want to chromatograph the neat material, talk to the column vendors to see if they have a suggestion.

Derivatization is probably a better option. If you pursue that route, think about using SPME where the fiber has the reagent on board. You could talk to Supelco about such a fiber or go all the way to Waterloo to pursue this option.

Sorry I could not provide more assistance.

Thanks AICCM for your reply.

As it turns out, I can easily go to Waterloo and talk to their SPME guru. I will see if they have something.

Carol

Hi Carol

On a recent purge and trap analysis of dried urine I got both urea and cyanuric acid off a non-polar column, but the peaks were hideously front tailed from overloading as you would expect.

If you do find a GC method, please post it, I'd be really interested.

Peter

cmoral,

Peter raises an excellent point that I had not thought about. Many compounds you would not expect chromatograph reasonably well on thick film non-polar columns. Headspace extraction on a 7 micron film -1 or -5 type column would probably work. You would still need to use an appropriate detector though (FID will probably not work.) AID, HID, PID, TSD, and NCLD would all probably work although there is a huge range of price and complexity listed herein. FID with a methanizer might also work if you have one.

Interested to hear about your progress.

Best regards.

Thanks Peter and AICCM for your replies. I am beginning to wonder if trying to convert the urea to ammonia and analyzing the ammonia is the easier way to go. The samples are liquid urine/manure which may have some urea in it but with so much water not sure if ammonia will volatilize out of the samples enough.

Restek informs me that their RTX-1 column will detect ammonia and I could use a TCD for a detector. Not sure of the sensitivity but the ammonia in the samples would probably be in the % range. We have a TCD that I am trying to get up and running. We can convert urea to ammonia using the enzyme urease then analyze the gas for ammonia. Am still looking into an SPME method to analyze for either.

Will keep you posted.

Carol

cmoral,

Have not seen ammonia on a -1 but I suspect that it will work with a thick enough film. I believe you can also use a Q plot column or a VolAmine (although that one is a bit expensive.)

If in the percent levels a TCD should probably work just fine.

Best regards.

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

Hello,

maybe to resolve your problem you can use the PID