Solid-phase test reagent for determination of nitrite and nitrate

A non-toxic solid-phase test reagent for rapid determination of nitrite and nitrate was developed. Powdered reagent utilised azo-and diazo-components (p-nitroaniline and chromotropic acid, respectively), solid organic acid acidifier (malonic, maleic or oxalic acid), zinc dust (for nitrate determination), catalyst and masking agent. Effects of solid acidifier and the amount of Zn reducing agent were evaluated. The optimal reagent formulation was established in terms of dynamic range and response kinetics, and validated by parallel measurements in split samples using an accredited ion-chromatographic method. The optimal reagent contained malonic acid as acidifier and 1.0% of Zn reducing agent, and showed good sensitivity for the determination of nitrite (LOQ of 0.03 mg L-1) and nitrate (LOQ of 0.17 mg L-1), and fast analysis time of under 6 min. These reagents were shown to be stable for at least 3 months with RSD of < 3%.