Properties of a novel linear sulfur response mode in a multiple flame photometric detector

A new linear sulfur response mode was established in the multiple flame photometric detector (mFPD) by monitoring HSO* emission in the red spectral region above 600 nm. Optimal conditions for this mode were found by using a 750 nm interference filter and oxygen flows to the worker flames of this device that were about 10 mL/min larger than those used for monitoring quadratic S2* emission. By employing these parameters, this mode provided a linear response over about 4 orders of magnitude, with a detection limit near 5.8 × 10−11 gS/s and a selectivity of sulfur over carbon of about 3.5 × 103. Specifically, the minimum detectable masses for 10 different sulfur analytes investigated ranged from 0.4 to 3.6 ng for peak half-widths spanning 4–6 s. The response toward ten different sulfur compounds was examined and produced an average reproducibility of 1.7% RSD (n = 10) and an average equimolarity value of 1.0 ± 0.1. In contrast to this, a conventional single flame S2* mode comparatively yielded respective values of 6.7% RSD (n = 10) and 1.1 ± 0.4. HSO* emission in the mFPD was also found to be relatively much less affected by response quenching due to hydrocarbons compared to a conventional single flame S2* emission mode. Results indicate that this new alternative linear mFPD response mode could be beneficial for sulfur monitoring applications.