Sequential flow injection analysis of ammonium and nitrate using gas phase molecular absorption spectrometry

A flow injection method on the basis of gas phase molecular absorption is described for the sequential determination of ammonium and nitrate. Two hundred microliters of sample solution is injected into the flow line. For ammonium determination, the sample zone is directed to a line in which reacts with NaOH (13 M) and produces ammonia. But for nitrate determination, the sample zone is passed through the on-line copperized zinc (Zn/Cu) reduction column and produces ammonium ion and in the follows ammonia. The produced ammonia in both cases is purged into the stream of N₂ carrier gas. The gaseous phase is separated from the liquid phase using a gas-liquid separator and then is swept into a flow through cell, which has been positioned in the cell compartment of an UV-Vis spectrophotometer. The absorbance of the gaseous phase is measured at 194 nm. Under selected conditions for sequential analysis of ammonium and nitrate, linear relations were found between the peak heights of absorption signals and concentrations of ammonium (10-650 μg ml⁻¹) and nitrate (20-800 μg ml⁻¹). The limit of detections for ammonium and nitrate analysis were 8 and 10 μg ml⁻¹, respectively. The relative standard deviations of repeated measurements of 50 μg ml⁻¹ of ammonium and nitrate were 2.0, 2.9%, respectively. Maximum sampling rate was about 40 samples/h. The method was applied to the determination of ammonium in pharmaceutical products and the sequential determination of ammonium and nitrate in spiked water samples.     

Reaktionen an komplexgebundenen liganden : XIV. Basenkatalysierter H—D-austausch und disproportionierung von komplexgebundenem diimin in μ-N2H2[Cr(CO)52; modellreaktionen der enzymatischen N2-fixierung

Complexed diimine in μ-N₂H₂[Cr(CO)₅]₂ undergoes a rapid H — D-exchange with deuterium ions, which is inhibited completely by acids; the rate of the H — D exchange is significantly larger for the diimine complex that for the corresponding hydrazine and ammonia complexes, which is explained by the acidic properties of the diimine protons. In the presence of catalytic amounts of strong base N₂H₂[Cr(CO)₅]₂ disproportionates fast and irreversibly to N₂[Cr(CO)₅]₂ and N₂H₄[Cr(CO)₅]₂; a mechanism is proposed for this reaction. The reactions of the complexed diimine are compared to those of the free diimine; their significance with respect to intermediated steps of the enzymatic N₂ fixation is discussed.     

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