Combined PFPD–FID assessment of sulfur in liquid fuels

A pulsed flame photometric detector (PFPD) was calibrated using standard sulfur compounds present in gasoline and diesel fuels, in combination with a flame ionization detector (FID). Gasoline range standards were added to a hydrocarbon mixture simulating gasoline, with individual sulfur concentrations from 3 to 80 ppm. Diesel range standards were added to a low sulfur commercial diesel fuel, with sulfur concentrations from 10 to 100 ppm. In gasoline, both the chromatographic areas calculated with the linearized signal (data points elevated to a given power), and reported by the instrument were regressioned with the sulfur mass concentrations. In both cases the areas were normalized with the FID areas to reduce deviations. Results were better when using the linearized signal. Only the normalized areas calculated with the linearized signal can be used in the case of the diesel, due to significant peak coelution. Individual calibration coefficients were calculated for each standard, but overall coefficients can be used safely in each of the boiling ranges. The compliance of regulations about sulfur was verified in commercial fuels and the different sulfur compounds were inspected. The simultaneous combined FID-PFPD use allows adding the sulfur to the conventional analysis of liquid fuels (e.g. composition, simulated distillation).

► Combined PFPD-FID in a GC can add sulfur analysis to standard analysis of liquid fuels.
► The FID area was used as a normalization parameter improving the sulfur analysis quality.
► The optimized PFPD response-sulfur mass relationship was not purely quadratic.
► PFPD calibration using the detector output signal was better than using reported areas.