Time-resolved spectroscopy of a homogeneous dielectric barrier discharge for soft ionization driven by square wave high voltage

Abstract

Helium capillary dielectric barrier discharge driven by the square wave-shaped high voltage was investigated spatially and temporally by means of optical emission spectroscopy. The finding of the previous investigation conducted with the sinusoidal-like high voltage was confirmed, i.e., the plasma in the jet and the plasma in the capillary constitute two temporally separated events. The plasma in the jet occurs prior to the discharge in the capillary and exists only during the positive half period of the applied high voltage. The time delay of the capillary discharge with respect to the discharge in the jet depended on the high voltage, and it was between 2.4 and 8.4 μs for the voltage amplitude change in the range from 1.96 to 2.31 kV, respectively. It was found that, compared to sinusoidal-like voltage, application of the square wave high voltage results with stronger (~6 times) He line emission in the jet, which makes the latter more favorable for efficient soft ionization. The use of the square wave high voltage enabled comparison of the currents (~1 mA) flowing in the capillary during the positive and negative high voltage periods, which yielded the estimation for the charge dissipated in the atmosphere ((4 ± 20 %) × 10(-11) C) through the plasma jet.

An experimental study on the influence of trace impurities on ionization of atmospheric noble gas dielectric barrier discharges

“…These early emissions, in particular, the plasma jet, play a key part in the soft ionization process for molecular mass spectrometry and were the focus of previous studies. [17][18][19] The coincident plasma on the other hand can be attributed to a dissociative character unwanted in most soft ionization processes. 16 While it was already shown that the intensity of this plasma strongly depends on the charge coupled to the DBD and could be enhanced significantly by increasing the total electrode width of the used DBD, the mode change from an early soft plasma to a dissociative coincident plasma can only be understood with the ionization of the trace impurities.…”

Capillary Dielectric Barrier Discharge: Transition from Soft Ionization to Dissociative Plasma

“…The spatial and temporal distribution of the intensities of the He 706 nm line and N 2 + molecular band at 391 nm are displayed in Figure B,C, respectively. They both show the early plasma (indicated with a dotted line in Figure B) formation which precedes the electrode plasma ignition in the capillary that coincides with the discharge current. In this early stage ( t < 0.5 μs), no significant emission from the dissociation products (F, Cl) of the analyte (CHClF 2 ) could be observed in the capillary.…”

Analytical Methodologies for Agrometallomics: A Critical Review

“…The commonly used structures of DBD can be identified as a planar and cylindrical configuration regardless of the surface DBD (surface discharges) and capillary DBD. 82,83 93 Like LA-ICP-MS, the microplasma by DBD can be used for elemental ablation on the solid surface following ICP-MS (Au, Ni, and Cu) or AFS (Hg). 94,95 Although the excitation power of DBD is obviously weaker than that of LA, the solid sampling DBD technique is still capable of giving elemental mapping information to some extent on the solid surface.…”

“…The reactive free radicals, energetic electrons and ions, excited state species, and ultraviolet light generated in the plasma enable elemental analysis. The commonly used structures of DBD can be identified as a planar and cylindrical configuration regardless of the surface DBD (surface discharges) and capillary DBD. , In 2001, DBD was first utilized for diode laser spectrometry; in 2006, Zhang et al used atmospheric pressure DBD as an atomizer for AAS and AFS; − up until now, DBD has been utilized as an ionization source for the mass spectrometer, excitation source for OES or induced source for CVG, , and gas phase enrichment (GPE) device for elemental analytes. ,, However, considering the vulnerability of microplasma, CVG such as HG and UVG is the most frequently used sampling method for DBD atomization or excitation to analyze the liquid or slurry sample. To directly analyze the solid sample, Liu and Mao employed a quartz tube ETV to introduce Hg and a DBD tube to degrade gaseous organic interferents for Hg analysis in food samples by AFS; for another, Jiang et al fabricated an ETV coupled with DBD-OES for the direct solid sampling analysis of Hg, Cd, and Pb in soil .…”