The Three-Electrode Direct Current Argon Plasma Studies in Discrete Sample Introduction, Mathematical Correction of Drifted Plasma Data, and Organic Solvent Introduction Effects in the Plasma (DC Plasma)

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Description: The Three-Electrode Direct Current Argon Plasma (DCP) is a well accepted excitation source for atomic emission spectrometry. Yet a variety of studies need to be performed in order to increase our fundamental knowledge of this source and to further improve its analytical capabilities. This thesis investigates three areas of research with the DCP. The first area examines discrete sample introduction into the DCP. Discrete sampling, well known for its sample conservation advantage, has been used with flame atomic absorption and inductively coupled plasma emission spectroscopies but no work has been published on using this sampling mode with the DCP. Discrete sample introduction is compared here to the standard continuous sampling mode. An unique sample drop generator is described and characterized. Results are given for a variety of system effects and used to explain the effect of sample drop size on emission intensity. The second area of research involves the use of mathematical correction techniques for removing the effect of plasma emission drift from analytical data. Previous techniques have been quite impressive at giving a good return of analytical accuracy but the nature of the correction methods distort the original precision values. Digital filtering techniques are presented here that greatly improve the return of the original accuracy and precision of sample values determined during periods of emission signal drift. The introduction of hydrophobic samples into the DCP is the last area examined in this thesis. Organic matrices are routinely run on the DCP but they can be prone to little understood matrix interference effects. A modified sample introduction chimney was designed that largely eliminated the carbon buildup encountered with the standard chimney permitting extensive studies using organic solvents with the plasma. It was found that the analytical emission zone of the plasma appears to be spatially tied to the plasma core. Matrix induced shifts in the plasma core, therefore, change the position on which the analyte emission spatial profile is observed. This, along with variations in nebulization efficiency, can cause analytical errors due to matrix changes. A simple model demonstrates that the severity of the effect depends, among other things, on where on a spatial profile one is before the spatial shift takes place.
Language: English
Format: Degree Work