A fluorescent nitrate sensing system using a reaction cartridge and titanium trichloride

A simple and highly sensitive cartridge type nitrate sensing system was developed using titanium trichloride (TiCl3) in hydrochloric acid to reduce nitrate to ammonium ion. The system primarily consisted of a nitrate reduction section using titanium trichloride and an ammonia detection section. The nitrate was reduced in a simply made cartridge equipped with filter units and the resulting ammonium ion solution was directly introduced into a flow injection system, where it was neutralized to ammonia and allowed to react with o-phthalaldehyde (OPA). The isoindole thus formed was detected by virtue of its fluorescence, allowing quantitation of the nitrate in the initial sample. Our sensing system has a detection limit of 0.01 mg l−1 and a dynamic linear range from 0.05 to 2.5 mg l−1 with response times of less than 5 min for the entire procedure. The system had a relative standard deviation (RSD) of less than 2.56% after more than 30 consecutive measurements of 0.5 mg l−1 NO3−. The system is unaffected by FeCl3, Na2SO4 and NaCl at concentrations of 200 mg l−1 or by biological oxygen demand (BOD) values as high as 110 mg O l−1. The effects of reaction time and titanium trichloride concentration were also investigated. Furthermore, several river water samples were examined.