Evaluation of the Mini-Hollow Cathode Emission Source for the Analysis of Microsamples

Abstract

The analysis of very small samples by atomic emission from a hollow cathode discharge source is investigated. Subpicogram detection limits of 0.88, 0.72, 0.38, and 0.70 pg are reported for Li, Na, K, and Ca, respectively, by viewing the excitation from a very small hollow with a custom-built multichannel spectrometer. These detection limits are comparable to those from electrothermal atomic absorption, with the additional advantage of the ability to analyze nonmetals. The technique has adequate sensitivity for the analysis of microsamples of physiological fluids for Na, K, and Ca; similar methods may be successful for Mg, P, and Cl, which are of significant physiological interest. Literature of applications of the hollow cathode as an emission source is reviewed. Instrumentation, operation, and sample preparation procedures are described. Temporal profiles of the emission from very small samples deposited in the hollow and working curves are given.

An atmospheric pressure glow discharge optical emission source for the direct sampling of liquid media

“…7,8 It is natural to wonder if the scope of application of GD devices can be extended to liquid-phase samples. [9][10][11][12][13][14] This is not unlike the attempts to deliver solid-phase originating samples into atmospheric pressure plasma sources (instead of the more natural solution introduction methods) by means of laser ablation or slurry aspiration. 15,16 While the cathodic sputtering in traditional GD sources effectively yields neutral atoms and molecules from solid matrices, the discharge's gas phase temperature (300-500 K) and low density are insufficient to affect desolvation of analytes introduced in water vapor, for example.…”

“…A good deal of effort has been devoted to developing strategies of introducing liquid-originating analytes into the discharge environment. [9][10][11][12][13][14] In an approach similar to that used in graphite furnace AAS, drying an aliquot of the analytecontaining solution on a suitable target cathode provides the GD with a dry residue sample that can be sputtered into the plasma. 9,10 In this way solvent vapors, which have a deleterious effect on GD source energetics, 17,18 are excluded from the discharge volume.…”

“…[9][10][11][12][13][14] In an approach similar to that used in graphite furnace AAS, drying an aliquot of the analytecontaining solution on a suitable target cathode provides the GD with a dry residue sample that can be sputtered into the plasma. 9,10 In this way solvent vapors, which have a deleterious effect on GD source energetics, 17,18 are excluded from the discharge volume. While effective for the sensitive analysis of small volume (v10 mL) samples, this approach is laborious and is not suitable for the analysis of flowing streams such as liquid chromatograph eluents.…”

An Atmospheric Pressure Glow Discharge Optical Emission Source for the Direct Sampling of Liquid Media

“…Although the cathodic sputtering event entails sufficient energy to release neutral atoms and molecules from solid matrixes, the discharge's gas-phase temperature is insufficient to affect desolvation of analytes introduced in water vapor, as is typical in atmospheric pressure flames and plasmas. As such, a good deal of effort has been devoted to developing strategies of getting liquid-originating analytes into the discharge environment. − The most common method involves drying an aliquot of analyte-containing solution on an inert target that is subsequently introduced as the cathode of the GD source, and the dried residue is sputtered from its surface. , In this way, solvent vapors are excluded from the discharge volume, and the plasma is operated much in its normal manner. Although effective, this approach is laborious and is not amenable to what would ideally be the analysis of flowing streams, such as liquid chromatograph eluents.…”

“…As such, a good deal of effort has been devoted to developing strategies of getting liquid-originating analytes into the discharge environment. [8][9][10][11][12][13] The most common method involves drying an aliquot of analyte-containing solution on an inert target that is subsequently introduced as the cathode of the GD source, and the dried residue is sputtered from its surface. 8,9 In this way, solvent vapors are excluded from the discharge volume, and the plasma is operated much in its normal manner.…”