Rapid and selective determination of ammonium by fluorimetric flow injection analysis

Selective and sensitive procedures for the determination of ammonium in riv er water and diluted urine were developed by using flow injection analysis equipment. The methods are based on the derivatization of ammonia with o-ph thaldehyde (OPA) and thioglycolate under alkaline conditions. The formed is oindole derivative is detected fluorimetrically at an excitation wavelength of 415 nm and an emission wavelength of 485 nm. The derivatization only ta kes 15 to 20 s at room temperature to achieve the maximum sensitivity. The optimized OPA reagent shows a surprisingly high selectivity for ammonium in the presence of many primary amines. With respect to the analysis of turbi d and fluorescent sample solutions the selectivity can be improved by separ ating the ammonia through a microporous membrane from the OPA reagent. With out this separation step ammonia can be detected in the range between 0.05 and 100 mu M with excellent linearity. After the insertion of an optimized membrane separation cell ammonia can be determined in the linear range betw een 0.2 mu M and 20 mM.