By virtue of the underlying fundamental process, speciation via atomic spectroscopy methods is only accomplished by inference from empirical formulae. The coupling of particle beam sample introduction and hollow cathode optical emission spectroscopy (PB/HC-OES) is applied here for empirical formula determinations of a group of organoselenium compounds. In this application, the carbon and hydrogen optical emission from the organoselenium compounds was monitored and the analyte element response (C (I) and H (I)) to glow discharge operation conditions was studied. Analytical response curves for integrated C and H emission intensities, as a function of both single analyte (selenomethionine) concentration and the empirical formula of the model compounds, were obtained. In all cases, a variability of less than 10% RSD for triplicate injections of 200 µL samples is observed. The detection limits of 0.16 ppm of selenomethionine (0.05 ppm of elemental C) and 0.034 ppm of selenomethionine (0.0019 ppm of elemental H) were obtained over the concentration range of 0.01–1000 ppm. Within the 100 µL injections, these values equate to absolute masses of 16 ng of selenomethionine (i.e. 5 ng of elemental carbon) and 3.4 ng of selenomethionine (i.e. 0.2 ng of elemental hydrogen). The corresponding detection limits for the selenium content in Se-(methyl)selenocysteine were determined to be 11 ng of elemental Se. The correlation of H (I)/C (I) emission intensity values to the atomic H/C values in different organoselenium compounds demonstrates that the PB/HC-OES system is capable of selenium speciation by means of the determination of empirical formulae.