Selective flow injection procedures for the determination of nitrogen containing analytes by gasdialytic-fluorimetric detection of enzymatically generated ammonia

Selective flow injection (FI) procedures were developed for the determination of organic nitrogen compounds, from which ammonia can enzymatically be released. The generated ammonia is detected after gasdialytic separation and derivatization with a totally aqueous o-phthalaldehyde (OPA) reagent. Ammonia can be determined in the range between 10−7 and 10−3 M and between 10−6 and 10−3 M after the gasdialytic separation. Immobilized amidohydrolases and amino acid oxidases are applied to determine urea, L-glutamine, L-glutamate, L-lysine and L-alanine. An automated four-channel FIA set-up was developed for the sequential determination of ammonia, glutamine, glutamate and alanine. A gas dialytic procedure for the quantitative elimination of ammonia from sample solutions was developed. Up to 15 complete cycles of analysis can be performed per hour.