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

An improved flow-injection system with an AgCl(s) reactor is proposed for the spectrophotometric determination of total nitrogen in Kjeldahl digests of plant materials. After sample injection, the established sample plug is alkalinised and allowed to flow through the mini-column where Ag+ ions are displaced as the soluble [Ag(NH3)2]+ complex. Bromopyrogallol red and o-phenanthroline are then added and a coloured ternary complex is formed under neutral conditions. The system is very stable, and baseline drift is usually <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 to 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.