Enhancement of Chemiluminescence Intensity of S₂* in Non-premixed Hydrogen Microjet Flame in the Photometric Detector for Sulfur Detection

A transparent quartz rod (q) placed vertically on top of a non-premixed hydrogen microjet flame in a flame photometric detector (qFPD) was developed and evaluated for sulfur detection. The microjet flame burned around the quartz rod because of Coanda effect, forming an extended downstream flame zone with a relatively low temperature between 550 and 650 °C, which is favorable to the formation of S₂*. The emission intensity of S₂* and the signal-to-noise ratio (SNR) of sulfur response were enhanced 2.6- and 2.1-fold, respectively. It was found that the quartz rod of diameter 4 mm with a tip shape of semicircle placed 6 mm above the nozzle yielded the highest SNR. The limits of detection (LOD) for seven kinds of tested sulfur-containing compounds of qFPD were 0.3–0.5 pg S s^–1, which is 5–7 times better than that of commercially available FPD detectors (LOD: 1.6–2.8 pg S s^–1). The selectivity of sulfur over carbon was 10⁵ on qFPD when the SNR for the mass flow rate of S and C atoms was ∼3 times. It was the first time that a quartz rod was used vertically on top of a microjet hydrogen-rich flame in FPD to enhance the chemiluminescence of S₂* and improve the LOD down to 0.3–0.5 pg S s^–1.