Integrated flow analysis platform for the direct detection of nitrate in water using a simplified chromotropic acid method

Abstract

This work describes the first use of a direct nitrate analyser using chromotropic acid. A simplified chromotropic acid method eliminating several steps previously associated with this method is employed in the platform. In a sulphuric acid medium, chromotropic acid reacts with nitrate ions and produces a characteristic yellow colour associated with an absorbance band in the visible region (λ_max = 430 nm). The modified method allows for nitrate determination over the linear range 0.9–80 mg L⁻¹ nitrate with a limit of detection of 0.73 μg L⁻¹ nitrate. Validation was achieved by analysing water samples from various sources including groundwater, trade effluent and drinking water by the modified method and by ion chromatography. The method was implemented on a flow analysis platform incorporating a paired emitter–detector diode (PEDD) as the optical detector. An excellent correlation coefficient of 0.993 was obtained between the modified method and ion chromatography. The modified chromotropic acid method represents a rapid, simple, low cost technique for the direct determination of nitrate in water.