Spectral examination of a multiple-flame photometric detector for use in chromatography

Abstract

An examination of the emission spectra produced in a novel multiple-flame photometric detector (mFPD) was performed and directly compared to spectra obtained from a conventional single-flame FPD mode. Through monitoring a broad spectral range from 250 to 850 nm, it was found that the mFPD produces sulfur emission predominantly as S2*, but HSO* can also be isolated in the red spectral region. Further, phosphorus emission in the mFPD was found to stem from HPO*, while carbon emission was attributed to CH* and C2*. Finally, background emission in the mFPD was determined to be from OH*. Qualitatively, these finding agree very well with the species found in a conventional single-flame FPD. However, quantitatively, the mFPD spectra consistently produced analyte emission bands that were relatively more intense, by as much as a factor of 3. In contrast with this, hydrocarbon spectra in the mFPD yielded significantly reduced relative intensities, owing to decreased C2* emission. As well, aromatic and aliphatic hydrocarbons produced much more similar distributions of CH* and C2* emission in the mFPD than in the conventional single-flame FPD mode. The results indicate that a relative reduction of C2 radical and an increase of oxidized carbon in the analytical flame of the mFPD could play a central role in the observed quenching-resistant behavior of this detector.