I am using a nickel anode in an electrochemical cell to oxidize urea in very alkaline solutions (pH 13.5). I want to quantify urea before and after the experiment. Many different methods have been published for urea quantification, thus I am also wondering why there is not a standard for this measurement. I have used ammonia HACH kits and measured total nitrogen and total organic carbon using a Shimadzu instrument with little success. This may be due to my low urea concentration (1 ppm urea). I am wondering if others have done similar measurements using other methods.
Dear Sir. Concerning your issue about determination of urea by electrooxidation. Urea electro-oxidation reaction in alkaline medium is systematically analyzed by electrochemical impedance spectroscopy (EIS). The effects of polarization potential and KOH concentration on the impedance appearance are investigated. In the presence of urea, it is found that Nyquist plots exhibit two depressed semicircles, with one at higher frequencies stably locating in the first quadrant while the other’s location at lower frequencies varying between the first and second quadrant as the polarization potential changes. Results show both indirect and direct pathways proceed in urea electro-oxidation reaction. A mathematical model indicates the reverse loop in the Nyquist plots is attributed to CO2 poisoning on the catalyst, which is also validated by the followed chronoamperometric method. Moreover, the rate determining steps of urea electro-oxidation reaction is dependent on KOH concentration. The EIS technique gives a new sight to interpret the poor stability of urea electro-oxidation on nickel catalyst, and thus helps to explore a CO2-insensitive catalyst. I think the following below links may help you in your analysis:
http://www.sciencedirect.com/science/article/pii/S0013468616312270
https://link.springer.com/article/10.1007/s10800-016-0993-6
http://onlinelibrary.wiley.com/doi/10.1002/aic.690320906/full
Thanks
I think, you may go for NMR analysis. NMR measurements result in linear detection of all signals, regardless of amplitude. You may also consult the Patent EP 1338891 B1.
Dear Andrew,
as far as I can remember to my time as student, there is the so called biuret reaction resulting in a violet copper complex when urea is thermally treated in alkaline solution.
In the following link: https://en.wikipedia.org/wiki/Biuret_test
some possibilities to improve its sensitivity are mentioned, too.
I do not know if it works in your case, but I could imagine that determination via UV-VIS could be a way to look for urea derivatives besides the gaseous ones and thus a help to your problem.
Good luck
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