Analysis of Organic Compounds by Particle Beam/Hollow Cathode Atomic Emission Spectroscopy:  Determinations of Carbon and Hydrogen in Amino Acids

Abstract

A detailed evaluation of the analytical characteristics of a particle beam/hollow cathode glow discharge atomic emission spectroscopy (PB/HC-AES) system is described for applications in the area of organic sample analysis. The optimization of sample introduction, nebulization parameters, and glow discharge conditions was performed for the elemental analysis (focusing on C and H) of a group of amino acids. By use of a high-efficiency thermoconcentric nebulizer, analyte particles are introduced into a heated hollow cathode glow discharge source, in either flow injection or continuous-flow mode, for subsequent vaporization/atomization and excitation. Nebulization temperature, solvent composition, and liquid flow rate were studied to elucidate their roles in the ultimate analyte emission characteristics for organic compound analysis. The hollow cathode operating discharge current and gas pressure were optimized, with the general responses found to be similar to those for the case of metal analysis. Background interferences from solvent and additive media on carbon and hydrogen determinations were studied and substantially reduced. The analytical response curves for carbon and hydrogen present in amino acids were obtained using 200 μL injection volumes, showing less than 10% RSD for replicate injections over a concentration range of 10-250 ppm, with detection limits of 3 and 1 ppm, respectively, for C (I) and H (I) emission. Subsequent studies of the response of carbon and hydrogen emission signal intensities to differences in amino acid stoichiometries suggest a capability of the PB/HC-AES system for the determination of empirical formulas based on H (I)/C (I) intensity ratios.

Particle beam glow discharge mass spectrometry: spectral characteristics of nucleobases

“…The next development step for the methodology will focus on improving the sensitivity of the ion source to levels more in line with those needed for PCR‐derived nucleotides. Implementation of a hollow cathode source geometry as employed in PB‐HC‐OES experiments is expected to accomplish this goal as the plasma contains higher densities of energetic electrons 21,22. Future work will include analysis of sequence‐specific, mixed‐base pentanucleotides in order to characterize the fragmentation patterns for different base combinations.…”

“…The desire to make the GD source a multifaceted mass spectrometric analysis tool has led researchers to explore the possibilities of using the source for analysis of both inorganic and organic solutions. To this end, Marcus and co‐workers have demonstrated the use of the particle beam (PB) as a means of introducing liquid‐phase samples into GD sources 19–24. The PB interface, originally applied in the MAGIC/LC/MS approach of Willoughby and Browner,25 provides a means of introducing LC effluents into low‐pressure sources (i.e., electron impact and chemical ionization) while maintaining chromatographic characteristics such as retention and elution quality 26,27.…”

Simultaneous multielement detection in particle beam/hollow cathode-optical emission spectroscopy

“…The HC glow discharge design was altered slightly from the one employed in previous works [10][11][12][13][15][16][17][18][19]21,22]. The HC was machined from a bulk copper rod with an inner diameter of 3.5 mm Fig.…”

“…As stated previously, it is not sufficient to identify that a chromatographic fraction contains a particular metal, but the precise identity of the compound must be known. The concept of determining empirical formulae based on metal and non-metal responses has been demonstrated using the PB/ HC-OES system for various small organometallics and metalloproteins [11][12][13]17,18]. Previous PB/HC-OES work also illustrated the concept that total protein determinations can be performed based on C (I) emission, with detection limits in the single ng range [16].…”

“…Use of the PB allows work in an inert (discharge gas) atmosphere plasma, in the absence of solvent remnants, which makes it possible to detect "gaseous" elements and non-metals such as C, H, N, O, S, and P with high sensitivity. Previous experiments using monochromator detection system include determinations of metal salts and organometallic compounds, as well as the non-metal detection of proteins and amino acids based on C and H content [11][12][13][14][15][16][17][18]. Improvements have been made by substituting the monochromator with a polychromator, allowing for simultaneous, multielement detection, thus reducing data collection times, sample sizes, and the dependence on chromatographic retention times to substantiate elemental correlations.…”