Axially-Staggered-Trap Microplasma Source-Based Miniaturized Optical Emission Spectrometer for High-Performance Elemental Detection

To miniaturize a microplasma-based optical emission spectrometer with high performance, the spatial distribution of electron density and the spectral responses in a point-discharge (PD) microplasma were systematically studied. COMSOL simulations and simultaneous detection of atomic emission and absorption were designed for spectral characterization. The discharge region around the electrode tips exhibited the highest electron density and spectral intensity. Based on this, a critical excitation source was designed by sequentially arranging three PDs in a discharge chamber. They were symmetrically distributed and axially rotated 60° between each other, forming an axially staggered-trap microplasma source to improve excitation capability and efficiency. This design exposed all of the electrode tips and enlarged the discharge region along the sample transportation/excitation and spectral acquisition direction, forming a microplasma trap. Therefore, it could intercept most analytes and facilitate spatially uniform excitation and unobstructed acquisition of spectral signals from all the electrode tips. Besides, the array configuration enabled tandem excitation to further improve sensitivity. Through coupling with hydride generation for sample introduction, limits of detection of 0.4, 0.1, 0.03, 0.2, 0.1, 1, and 0.05 μg L^-1 were achieved for As, Ge, Hg, Pb, Sb, Se, and Sn, respectively, with relative standard deviations below 3% (n = 5). Compared with a conventional single PD, the analytical sensitivities were improved by 5-7 times, and additionally by 8-17 times with more (six) PDs. The accuracy and applicability were demonstrated by analyzing certified reference materials and real samples. It features compactness, low power consumption, and excellent performance, thus showing great promise for on-site elemental analysis.