Pulsed Flame Photometer Detector for Gas Chromatography

A new pulsed flame photometer detector (PFPD) design is described with improved performance. Detection limits of 180 fg/s (sulfur), 7 fg/s (phosphorus), and 2 pg/s (nitrogen) are demonstrated when 2 rms noise is considered as the detection limit The minimum detected amount of sulfur was further reduced with a sulfur doping method to about 30 fg/s. The factors affecting the selectivity are analyzed in terms of operating the PFPD as a specific detector without any hydrocarbon interferences. The effect of the pulsed nature of the PFPD on the chromatographic peak area and height reproducibility is modeled and analyzed. It is shown that above 3 Hz, the standard deviation of peak area is 2%, which is dominated by nondetector effects. The detector temperature effect was studied and is presented. The difference between light guide and lens optics is discussed. The column operation with hydrogen as a carrier gas is compared to that with helium, and the injection of chlorinated and fluorinated solvents is shown and discussed. New ways of obtaining additional information by using the added dimension of time are analyzed. It is shown how the simultaneous use of dual gates can provide unambiguous heteroatom identification. It is also described how a dual gate subtraction method results in a considerable enhancement of the interheteroatom selectivity, especially for phosphorus versus sulfur. The dual gate approach also provides up to an order of magnitude increase in the measurement dynamic range. Practical utilization of the PFPD is illustrated with the analysis of real-world samples, including thiophene in benzene, pesticides in a broccoli extract, and a sulfur-containing drug in human serum.