Pulsed-flame photometer: a novel gas chromatography detector

The pulsed-flame photometer detector (PFPD) is based on a flame source and combustible gas flow rate that cannot sustain a continuous-flame operation. Thus, the ignited flame propagates back to the combustible gas mixture source and is self-terminated after the combustible gas mixture is burnt. The continuous gas flow creates addltional ignitions in a periodic fashion. The maln feature that characterizes the pulsed-flame photometer detector is the pulsed nature of the emitted light. Time domain information is added to the heteroatom specific emission with time-dependent emission being observed. In this paper we describe the PFPD and evaluate its performance as a gas chromatograph detector. The main advantages of the PFPD include improved detection sensitivity for sulfur and phosphorus, much higher selectivity against hydrocarbon molecules, lower gas consumption, reduced emission quenching, additional temporal information, and the ability to detect selectively other heteroatoms such as nitrogen or the simultaneous detection of sulfur and carbon. Points for further examination are the emission dependence on the column flow rate and combustion cell surface effects on the pulsed flame emission. The minimum detection levels achieved are 2 X [10.sup.-13] g S/s, 1 X [10.sup.-14] g P/s, 5 X [10.sup.-12] g N/s and 6 X [10.sup.-11] g C/s. The PFPD is unaffected by the injection of large amounts of solvent including aromatic solvents, and both sulfur and phosphorus can be detected and quantified at sub-ppb concentration levels. The sulfur concentration dependence of the PFPD is quadratic, and its response is independent of the structure of the sulfur-containing molecule. The detector response time is fast enough to closely resemble the flame lonization detector for both sulfur and phosphorus molecules resolved chromatographically on a narrow-bore column. The operation of the PFPD on either S, P, N, C single-element channels or S + P, S + C, P + N, or S + P + N multielement detection modes is described and presented.
The advantages and diasadvantages of the operation of a pulsed flame photometer as a gas chromatography detector were derived. The photometer was evaluated based upon its performance in experiments involving the selective detection of sulfur, phosphorous, carbon and nitrogen by capillary gas chromatograpy. Several important advantages were assessed from the photometer. However, disadvantages were identified in the column flow and combuster surface effects.