Rapid and selective determination of ammonium by fluorimetric flow injection analysis

Abstract

Selective and sensitive procedures for the determination of ammonium in river water and diluted urine were developed by using flow injection analysis equipment. The methods are based on the derivatization of ammonia with o-phthaldehyde (OPA) and thioglycolate under alkaline conditions. The formed isoindole derivative is detected fluorimetrically at an excitation wavelength of 415 nm and an emission wavelength of 485 nm. The derivatization only takes 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 turbid and fluorescent sample solutions the selectivity can be improved by separating the ammonia through a microporous membrane from the OPA reagent. Without this separation step ammonia can be detected in the range between 0.05 and 100 microM with excellent linearity. After the insertion of an optimized membrane separation cell ammonia can be determined in the linear range between 0.2 microM and 20 mM.

Calibrationless Determination of Creatinine and Ammonia by Coulometric Flow Titration

“…The CIH reactor was used at the optimum pH 7.5. Figure 3 shows and at creatinine concentrations smaller than 1.0 mM, which was confirmed by fluorimetric detection of the released ammonia as described earlier (19). To the best of our knowledge, this is the first enzyme microflow reactor that converts creatinine both quantitatively and selectively.…”

“…The effluent of the reactor is adjusted to pH Ն12.25 to convert more than 99.9% of the ammonium into the volatile ammonia, which is quantitatively separated across a microporous Teflon membrane. This membrane is mounted into the thin-layer separation cell (17)(18)(19) shown in the blowup of Fig. 1.…”

A rapid and sensitive fluorometric assay method for the determination of nitrilase activity

“…The proposed method can overcome these shortcomings. Another rapid and sensitive method for determination of NH + 4 ions by fluorimetric flow‐injection analysis has been reported by Mana and Spohn [12]. Although both the present and the reported methods [12] are based on the same principle of formation of isoindole derivative, they differ substantially in their linearity ranges, i.e.…”

Extraction of ammonia and nitrite using modified magnetite iron oxide nanoparticles before spectrophotometric determination in different water samples

“…The allowable levels of ammonia concentration in fresh and drinking water are in the range of 0.5-3.0 mg L −1 depending on the local regulation of states and certain areas in the world [3]. The determination of ammonia at lower concentrations typically entails a chemical reaction to transform the analyte into a derivative amenable for colorimetric [1,[3][4][5], fluorimetric [6] or chemiluminescence detection [7]. In this sense, the reaction with indophenoltype reagents is still the most widely used approach [1,[3][4][5]8,9].…”