Determination of nitrate and ammonium ions in water samples by atmospheric pressure glow discharge microplasma molecular emission spectrometry coupled with chemical vapour generation

Abstract

In this paper, a low power atmospheric pressure glow discharge (APGD) microplasma source has been investigated for the determination of nitrate and ammonium ions with molecular emission spectrometry (MES) coupled with chemical vapor generation (CVG). Nitrate in samples was on-line reduced to NO by reaction with 15% (v/v) TiCl₃, while ammonium was on-line oxidized to N₂ by reaction with NaBrO. The generated vapor species of NO and N₂ were subsequently transferred into an APGD excitation source by argon and detected with a charge-coupled device (CCD) microspectrometer. The influences of operating parameters such as the sample flow rate, argon flow rate, discharge current and interference from concomitant elements were investigated using emission bands of NO at 237.0 nm and N₂ at 337.1 nm, respectively. The detection limits for the determination of nitrate and ammonium were 0.24 and 0.20 mg L⁻¹, respectively. The accuracy of the present CVG-APGD-MES method was demonstrated by the determination of nitrate and ammonium in certified reference materials. Furthermore, the proposed method was also successfully applied to the analysis of a series of environmental water samples.