Characteristics of liquid electrode plasma for atomic emission spectrometry

Abstract

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 Â 10 15 cm À3 . 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 mg L À1 for Pb.

Comparison of the Plasma Temperature and Electron Number Density of Pulsed Electrolyte Cathode Atmospheric Pressure Discharge and Direct Current Solution Cathode Glow Discharge

“…K and 5700519000678 K, respectively. Compared to the work of Yoshinobu Kohara [33] whose discharge system (LEP-AES) was driven by a high-voltage DC pulse power, the excitation temperatures of the pulsed-ECAD system were relatively lower than for LEP-AES (8000 K).…”

Atomic spectrometry updates: Review of advances in atomic spectrometry and related techniques

“…The argon plasma was operated at atmospheric pressure, 280 V (DC) and 8 mA, and excited emission at 253.6 and 469.4 nm to yield LODs of 68 ppb and 1.0 ppm for P and S, respectively, when using a palm-sized spectrometer for detection. A liquid electrode plasma (LEP) has been characterised for use in AES by Kohara et al 70 The plasma was generated directly in solution between two platinum electrodes, by applying a pulsed (3 ms) voltage of up to 2500 V in a narrow channel (100 mm) etched in fused silica. They observed the plasma and Pb emission at 405.78 nm using an array of detection equipment, including a high speed camera, CCD interface with a microscope, and a CCD spectrometer with a bre optic interface.…”

On-chip solid phase extraction–liquid electrode plasma atomic emission spectrometry for detection of trace lead

“…This is because the increase in applied voltage leads to the increase in current and temperature of micro-plasma, resulting in the increase of emission light intensity. 4,5) However in case of high voltage there is an expansion of LEP channel that leads to decrease of intensity. Figure 7 shows image of the narrow channel after 40 cycles with voltage of 1500 V. The white line indicates the initial shape of LEP narrow channel.…”