Spatially resolved measurements to improve analytical performance of solution-cathode glow discharge optical-emission spectrometry

Abstract

Past studies of the solution-cathode glow discharge (SCGD) revealed that elemental and molecular emission are not spatially homogenous throughout the source, but rather conform to specific zones within the discharge. Exploiting this inhomogeneity can lead to improved analytical performance if emission is collected only from regions of the discharge where analyte species emit strongly and background emission (from continuum, elemental and/or molecular sources) is lower. Effects of this form of spatial discrimination on the analytical performance of SCGD optical emission spectrometry (OES) have been investigated with an imaging spectrograph for fourteen atomic lines, with emphasis on detection limits and precision. Vertical profiles of the emission intensity, signal-to-background ratio, and signal-to-noise ratio were collected and used to determine the optimal region to view the SCGD on a per-element basis. With optimized spatial filtering, detection limits ranged from 0.09-360 ppb, a 1.4-13.6 fold improvement over those obtained when emission is collected from the full vertical profile (1.1-840 ppb), with a 4.2-fold average improvement. Precision was found to be unaffected by spatial filtering, ranging from 0.5-2.6% relative standard deviation (RSD) for all elements investigated, closely comparable to the 0.4-2.4% RSD observed when no spatial filtering is used. Spatial profiles also appear useful for identifying optimal line pairs for internal standardization and for flagging the presence of matrix interferences in SCGD-OES.

A novel solution cathode glow discharge geometry for improved coupling to optical emission spectrometry

“…Indeed, Schwartz and coworkers have shown that detection of atomic emission based on defined regions of interest within the SCGD increases S/N. 31 In addition, many authors have noted that AES signal increases with increasing SCGD discharge power until the discharge collapses through arc formation. 8 Recent studies have shown that the current density at the cathode surface remains approximately constant regardless of cathode size or shape, and thus increasing SCGD power is achieved by increasing cathode size.…”

“…Indeed, Schwartz et al have recently showed that SCGD limits of detection can be improved by 1.4–13.6-times by using spatially-dependent collection of SCGD emission. 31…”

Temporal characterization of fundamental plasma parameters in pulsed liquid electrode plasma (LEP) optical emission spectrometry

“…The 366 active LEP power is comparable to other solution-based microplasmas, for example, the SCGD 367 and the LS-APGD. Typical operating powers for the SCGD and LS-APGD are in the range of 368 60-80 W [35][36][37] and < 50 W [27,38], respectively. 369…”

The sensitive determination of Ag, Pb and Tl as well as reduction of spectral interferences in a hanging drop cathode atmospheric pressure glow discharge excitation microsource equipped with a Dove prism system

“…1 Since APGD operated in contact with owing solutions is rather non-uniform plasma, the spatially resolved acquisition may inuence the analytical response of this excitation source, as reported. 12,13 Therefore, an interesting modication of the optical system for APGD can be the application of a Dove prism (DP), which allows the rotation of the discharge image and inuences the measured signals.…”