Field detection of CODMn with portable optical emission spectrometer coupling with drone-based water sampler

Abstract

Permanganate index (COD_Mn) is one of the most important indicators to assess organic pollution in surface water, however, its determination is often limited by the potential risks associated with sample collection and analyte loss during sample storage and transport. Herein, a novel strategy combining drone-based sample collection with microplasma point discharge carbon optical emission spectrometry (μPD-C-OES) was described to effectively address these issues. The drone-based sample collection technique can follow preset routes to rapidly collect water samples at specified depths from various sites within a radius of 15 km, eliminating potential risks to operators and improving sampling accuracy. A miniaturized low-power μPD-C-OES device coupling with sealed-digestion chemical vapor generation (SD-CVG) can accomplish rapid field detection of COD_Mn via quantification of the volatile CO₂ produced from the oxidation of Na₂C₂O₄ by residual KMnO₄, thereby avoiding sample storage, transport, and analyte loss. Due to the high sensitivity of μPD-C-OES and highly efficient matrix separation provided by the CVG technique, a limit of detection (LOD) of 0.17 mg/L for COD_Mn was obtained, with relative standard deviations (RSDs, n = 11) better than 1.5 %. The practicality of this strategy was evaluated through the field analysis of water samples collected from a large reservoir and a river. The obtained results indicate that the proposed method not only facilitates safe, accurate and rapid water sample collection with precise GPS localization but also offers an innovative solution for the sensitive field detection of COD_Mn in surface water.