Development of a new liquid chromatography method for the separation and speciation of organic and inorganic selenium compounds via particle beam-hollow cathode glow discharge-optical emission spectroscopy

Abstract

A system for the separation and detection of inorganic and organic selenium compounds utilizing particle beam-hollow cathode glow discharge-optical emission spectroscopy (PB-HC-OES) as a selenium-specific detector has been investigated. The PB interface includes a thermoconcentric nebulizer to generate a finely dispersed aerosol, a heated metal spray chamber for desolvation, and a two-stage momentum separator, which removes solvent vapor. The resulting beam of dry analyte particles are introduced into a heated (∼250 °C) hollow cathode, where they are vaporized, atomized and excited within the plasma. Using LC-PB-HC-OES the following compounds were examined: selenocystine, selenomethionine, selenoethionine, sodium selenate, and sodium selenite. A reverse phase ion-pairing chromatography method was developed to separate these five compounds (both organic and inorganic), with UV absorbance monitored at 210 nm. The Se I 204.0 nm atomic emission intensity was then monitored by coupling the LC column with the PB-HC-OES system. Emission responses for the selenium of both the organic and inorganic compounds in flow injection mode using 200 µL injection volumes indicate detection limits of ∼200 ppb (100 ng) with less than 10% RSD variability for triplicate injections over a range of 200–1960 ng. The retention times of the five analyte peaks are similar to those detected by UV absorbance, demonstrating the ability of the PB interface to preserve the chromatographic integrity of the separation. Optical emission detection of liquid chromatographic separations of the selenium-containing compounds demonstrates the feasibility of the PB-HC-OES system as a simple selenium-specific detector for liquid chromatography.