possible to detect dihydrogen ammonium phosphate with UV?
Posted: Thu Oct 27, 2011 11:09 am
by jonocardiff
HI, I have been stuck in front of a Gilson HPLC set up with no prior experience or training! they have asked me to determine the concentration of a solution of dihydrogen ammonium phosphate (monoammonium phosphate), they have a Gilson UV detector 190-380nm, does anyone know if there will be a UV adsorption band? I can't find a UV spectra for the compound online. Thanks in advance!
Re: possible to detect dihydrogen ammonium phosphate with UV
Posted: Thu Oct 27, 2011 2:44 pm
by HPLCaddict
Phosphate salts, as ammonium phosphate, are used as buffers in HPLC-eluents because of their very low UV absorbance. Therefore, I don't think it's possible to quantitate it via UV
Re: possible to detect dihydrogen ammonium phosphate with UV
Posted: Thu Oct 27, 2011 3:05 pm
by Vlad Orlovsky
Not true about UV. You can do indirect detection of this salt. What you need is to use some UV active compound in mobile phase and see ammonium ion and phosphate ion as a negative peaks. In order to do this you need to separate them first. Something similar to these:
http://www.sielc.com/Application-HPLC-S ... isc-N.html
http://www.sielc.com/Application-Simult ... olumn.html
In your case you will need to use a different mobile phase which does not contain ammonium or sulfate and add UV active compound into mobile phase (phenol, benzonitrile. neutral dye, etc.). The method is not the best, because your base line will be noise. I don't know what kind of LOD/LOQ you can achieve with this approach but If you don't have access to ELSD or RI this is one of the approaches to try. Alternatively you can try one of the wet chemistry methods.