FLAME PHOTOMETRIC DETECTION OF SOME TRANSITION-METALS .2. ENHANCEMENT OF SELECTIVITY

A flame photometric detector was used in single-channel and in differential dual-channel modes to characterize and control its selectivity for various transition elements against a hydrocarbon background. The experiments included gas-chromatographable compounds of Cr, Mn, Fe, Co, Ni, Ru, Re, and Os. Single-channel dispersive modes brought only modest gains in selectivity vis-a-vis the non-dispersive (no optical filter) mode. In dual-channel differential modes, however, metal-carbon selectivities could be improved by factors of one to two orders of magnitude. The highest still measurable selectivity ratios are now in excess of 10(7). The differential dual-channel operation of the detector also made it possible to increase the selectivity of one hetero-element vis-a-vis another; and to distinguish between two hetero-elements, by oppositely directed peaks, in a (spectrally suppressed) matrix of carbon compounds. Metal-metal selectivities could be improved by factors of one to three orders of magnitude over the best dispersive single-channel modes.