Accurate spectral scans of single chromatographic peaks

Abstract

A detector equipped with two channels can fetch accurate luminescence spectra either from migrating chromatographic peaks or from other inputs of sharply varying concentration. To achieve this, one (the scanning) channel is continually referenced to another (the constant-wavelength) channel: the ratio of the two hence portrays correctly the intensity distribution of the spectrum. As a model system for testing this ratio approach on single gas chromatographic peaks, a flame photometric detector was connected to a 1 8 - m scanning spectrophotometer. No significant differences were found in relative spectral amplitudes between scanning the ascent versus the descent of a peak. Similar spectral constancy was obtained when scanning non-chromatographic variable inputs. With a view to practical use, three experiments were carried out that demonstrated the sensitivity and/or the spectral resolution obtainable from reference scans of single peaks. To wit, 5 pg of phosphorus produced a clearly recognizable HPO spectrum: the vibrational levels of S 2 resolved well; and the presence/absence of atomic iron lines confirmed an earlier postulated energy limit for the chemiluminescent excitation reaction.