Spectrophotometric determination of total nitrogen in plant materials using a flow-injection system with an AgCl(s) reactor

An improved flow-injection system with an AgCl(s) reactor is proposed for t he spectrophotometric determination of total nitrogen in Kjeldahl digests o f plant materials. After sample injection, the established sample plug is a lkalinised and allowed to flow through the mini-column where Ag+ ions are d isplaced as the soluble [Ag(NH3)(2)](+) complex. Bromopyrogallol red and o- phenanthroline are then added and a coloured ternary complex is formed unde r neutral conditions. The system is very stable, and baseline drift is usua lly <0.01 absorbance after 4 h operation periods. Precise results (R.S.D.<2 %) are obtained at a rate of 100 h(-1). The analytical curve is linear up t o 6.00% (w/w) N (dry basis), regression coefficient has been estimated as > 0.999 (n=6) and detection limit is 0.2% (w/w) N. Accuracy was confirmed by running standard reference materials and typical samples already assayed by conductimetry. (C) 2000 Elsevier Science B.V. All rights reserved.