Yasushi Terui

Characteristics of liquid electrode plasma for atomic emission spectrometry

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a recently developed elemental analysis method that uses microplasma. LEP forms in a vapor bubble generated inside a narrow-center microchannel by using high-voltage DC pulse power. We studied the characteristics of LEP and atomic emission of lead (Pb), as an example element, which has not been described in detail. We estimated the plasma parameters and observed the expansion and shrinkage of a vapor bubble with discharge as well as the time course and spatial distribution of the atomic emission of Pb (405.78 nm). The applied voltage was 2.5 kV and the pulse width was less than 3 ms, which produced a current of about 100 mA. We found that the excitation temperature was about 8000 K and the electron density was about 1 × 1015 cm−3. We also found that two quite different emission phases occurred separately during the time course. The first emission phase corresponds to the first expansion and shrinking of the bubble around atmospheric pressure and the second emission phase corresponds to the re-expansion of the bubble and emission at reduced pressure with higher atomic and lower background emissions. Maximum atomic and background emissions were observed at the narrowed center of the microchannel, but there was an additional local maximum atomic emission region at the anode side bubble–liquid interface where the background emission was very low, which would be a better condition for sensitive measurement. The limit of detection determined in our experiment was 4.0 μg L−1 for Pb.

Atomic emission spectrometry in liquid electrode plasma using an hourglass microchannel

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a new elemental analysis method that uses microplasma. LEP forms in a vapor bubble generated inside a narrow-center microchannel by using high-voltage DC pulse power. In this study, we used a novel hourglass microchannel having a 3-dimensionally and axisymmetrically narrowed shape, which caused a bright emission roughly 200 times that of the flat microchannel used in our previous study. We observed the spatial distribution of atomic emission and determined the limit of detection (LoD) by utilizing the confirmed spatial distribution. We found that the spatial distribution of atomic emission for 41 elements in our experiments could be classified into three patterns in accordance with a maximum emission point: anode side, narrow-center, and cathode side. Atomic emission was measured at the maximum emission point and the calibration curve for each element was made to determine the LoD. The LoD of 25 tested elements in our experiment ranged from 1 μg L−1 for Li to 306 μg L−1 for V.