INVESTIGATIONS OF THE USE OF INDUCTIVELY COUPLED PLASMA EMISSIONS FOR CHEMICAL ANALYSIS

Abstract

Investigations of new applications of the inductively coupled plasma (ICP) for analytical atomic emission spectroscopy are performed. Research efforts are focused in three major areas: emissions below 185 nm, analysis of wear metals in lubricating oils and use of the ICP as a selective detector for high performance liquid chromatography (HPLC). A unique plasma coolant tube containing a side arm which allows direct observation of the discharge is used to investigate emissions in the vacuum ultraviolet (VUV) spectral region between 120 and 185 nm. Emissions from elements which do not emit radiation in the visible region are observed. Oxygen emissions at 130 nm, nitrogen at 149 and 174 nm and carbon at 155 and 165 nm make up the background spectrum. These elements are present as impurities in the argon gas used to sustain the ICP discharge. Fifteen emission lines from bromine are observed. Those at 153 and 163 nm are the most intense. Sulfur also has fifteen emission lines and chlorine has nine in this region of the spectrum. The VUV region is found useful for observation and potential analysis of many elements. A heated sample introduction system attached to a Babington nebulizer is investigated as a means to aerosolize lubricating oils for introduction into the ICP. This allows direct analysis of wear metals in oil samples without requiring the usual sample dilutions. Several commercial brands and weights of motor oil are spiked with iron in order to evaluate this system. Heating the oil as it enters the nebulizer is found to increase the nebulization efficiency as much as sixtyfold in some cases. Differences in nebulization efficiency due to viscosity are almost entirely eliminated through the application of heat. A linear calibration curve extending three orders of magnitude from a detection limit of one ppm iron is determined. The ICP is used as a selective detector for HPLC. Nucleotides separated by anion exchange chromatography are determined in the ICP by observing phosphorus emissions. Methanol and acetonitrile used for reverse phase HPLC are successfully run in the IPC. The method is evaluated by using the ICP to determine phosphorus in compounds separated by using reverse phase conditions. The HPLC is used to separate organic interferences from several silicone samples using reverse phase conditions allowing the ICP to accurately analyze silicon content.