Determination of nitrites and nitrates in plasma-activated deionized water by microchip capillary electrophoresis

In this work, we present the application of a fast and sensitive microanalytical method, microchip capillary electrophoresis (MCE), for the determination of NO₂⁻ and NO₃⁻ ions in deionized water treated by atmospheric pressure plasma jet (APPJ). The MCE technique consisted of an online combination of isotachophoresis with zone electrophoresis, both performed on the microchip. The argon plasma has been characterized by optical emission spectroscopy (OES) and Fourier transform infrared spectroscopy (FTIR). OES confirmed the presence of argon excited species (Ar I) emission (4p → 4s) lines, N₂ emission bands (second positive system C³Π_u → B³Π_g), and OH band (A²∑⁺ → X²Π Δv = 0), as well as the presence of NO and excited NO₂. The presence of NO₂ molecules was also confirmed by FTIR absorption spectroscopy. The performance of the developed MCE method was evaluated for linearity, limit of detection, limit of quantitation, precision, and accuracy, and the concentration of NO₂⁻ and NO₃⁻ in the water as a function of the water treatment time was monitored.