Spectrophotometric determination of ammonium by an rFIA assembly

Abstract

[EN] The paper deals with the spectrophotometric determination of ammonia with a reverse Flow Injection Analysis assembly. The procedure is based on the modified reaction of Berthelot in which the sample acting as carrier merges with NaClO in basic medium; then a second reagent (salicylic acid, sodium hydroxide and sodium nitroprusside) is inserted into the resulting mixture. The calibration graph was linear from 0.5 to 20 ppm; L.O.D. 0.3 ppm NH4+; the sample throughput was 32 h(-1) and the repeatability was 0.7% (n = 9, 5 ppm). The day-to day reproducibility resulted in an RSD of the slope of 4.2% (n = 8). The method was applied to fertilizers and pharmaceutical formulations. The separation and pre-concentration of the analyte was also tested by addition of a separation device in which the ammonia passed into an acceptor solution containing a pH indicator and the calibration graph obtained was linear from 0.1 to 5 ppm NH4+.