THE GLOW DISCHARGE - A MULTIFACETED OPTICAL EMISSION SOURCE: FROM SOLIDS ANALYSIS TO METALLOPROTEINS

Glow discharges (GD) are well known for their application to direct solids elemental analysis of metals and alloys by optical emission spectroscopy (GD-OES). The most successful application of GD-OES has been the analysis of solid materials since the GD provides rapid, direct bulk and depth profiling analysis of solids, metals, powders, polymers, glasses and ceramics. However, solids analysis has typically suffered from the lack of true analytical blanks and the inability to study particulate solids in their native state. An approach for the analysis of solid powdered material entrapped in a sol-gel matrix by radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is described. Using the sol-gel method, analytical blanks were obtained by the use of an undoped sol-gel. Through sol-gel chemistry, entrapment of solid powdered material (i.e., Portland cement and oligonucleotides) in a solid glass matrix is achieved. Slurries of powdered materials were incorporated into the films and analyzed for both metallic and non-metallic elemental components. Rf-GD-OES is capable of easily determining non-metals due to the inert atmosphere. Cast films are analyzed to determine the optimum discharge operating conditions and effects of particle size as well as deposited layer thickness. Even though depth profiling of solid layered surfaces and thin films has been the major area of application for GDs, recent trends have focused on the analysis of liquid solutions for elemental species studies. The coupling of particle beam sample introduction and hollow cathode optical emission spectroscopy (PB/HC-OES) is applied for empirical formula determinations of a group nucleotides. The phosphorous and carbon atomic emission from ribonucleotide compounds is monitored and the analyte element response (P (I) and C (I)) to the glow discharge operation conditions is studied. To further demonstrate the capability of the PB/HC-OES as a liquid chromatography detector for biomolecules, iron containing metalloproteins were separated and determined by PB/HC-OES through monitoring of iron atomic emission. Reversed phase high performance liquid chromatography is used to separate and isolate an iron-protein mixture followed by PB/HC-OES iron specific detection. Parametric optimization for sample introduction, nebulization and hollow cathode source conditions are performed for the analysis of iron-containing metalloproteins