Novel Multiple Flame Photometric Detection Methods for Gas Chromatography

Abstract

This thesis describes the advancement of a multiple flame photometric detector (mFPD) for gas chromatography (GC). The mFPD modes characterized in this study show great improvements (e.g. up to 20 fold better sensitivity) over its initial prototype, demonstrating similar (and enhanced) performance attributes (e.g. up to 100 fold better quenching resistance) relative to other GC detectors for the selective determination of sulfur and phosphorus compounds. Through monitoring HSO* emission in the device, a linear sulfur response was found that demonstrated a detection limit of 5.8 × 10−11 gS/s, a selectivity of S/C of 3.5 × 103, and fast GC response dynamics. Notably, however, this mode provided enhanced response uniformity and reproducibility (e.g. 1.7% average RSD values and 90% of compounds ± 0.1 of unity response), as well as significant resistance toward interference from hydrocarbon quenching (e.g. signal observed down to 50 ng of analyte). Next, emission spectra of the mFPD were acquired and examined for the first time. It was found that the mFPD produces sulfur emission 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*. Results indicate that a relative reduction of C2 radical and an increase of oxidized carbon in the mFPD could play a central role in the quenching-resistant behavior of this device. Finally, a new mFPD design was introduced based upon interconnecting fluidic channels within a planar stainless steel (SS) plate. Relative to the initial mFPD prototype, the SS mFPD provided a 50% reduction in background emission levels, easier operation, and better signal collection properties. As a result, sulfur response in the device yielded a detection limit of 9 × 10−12 gS/s while also providing large resistance to hydrocarbon response quenching. Furthermore, this SS mFPD design uniquely allows analyte emission monitoring in multiple worker flames for the first time. In all, the new mFPD that has been characterized in this study can serve as a useful alternative method of detection for sulfur and phosphorus applications by providing more versatile monitoring options.