Point Discharge Microplasma Optical Emission Spectrometer: Hollow Electrode for Efficient Volatile Hydride/Mercury Sample Introduction and 3D-Printing for Compact Instrumentation

A miniaturized optical emission spectrometer was constructed with improved point discharge microplasma as an excitation source to enhance sample introduction efficiency and excitation efficiency. By using a hollow electrode as one of the discharge electrodes, analyte-containing chemical vapor yielded via hydride generation was transported and confined into the hollow electrode and subsequently guided into the microplasma with high sample introduction efficiency. Moreover, gaseous analyte species were directly diffused from inside the electrode into the center of the microplasma, instead of traditional external diffusion into the microplasma, resulting in sufficient participation in interactions and excitation in the plasma; thus, high excitation efficiency and stability can be achieved. A 3D-printing technique was used to fabricate some components for compact integration of this spectrometer. Physical characteristics of the microplasma, 3D-printing, and experimental parameters were all investigated to better understand the excitation capability and obtain optimal analytical performance. Under optimized conditions, As, Bi, Ge, Hg, Pb, Sb, Se, and Sn were successfully detected, with detection limits of 2.5, 0.44, 1.6, 0.10, 2.8, 1.5, 31, and 0.24 μg L^-1, respectively, and relative standard deviations all less than 4%. It was applied to the analysis of Certified Reference Materials (water, soil, and biological samples) and real water samples with satisfactory results. Because of its advantages of compactness, robustness, easy fabrication, and cost-effectiveness, it has a great prospect as a portable spectrometer for field analytical chemistry.