Anal. Chem. 1995, 67,3305-3318
Pulsed Flame Photometer Detector for Gas Chromatography Aviv AmiraP and Hongwu Jing School of Chemisty, Sadder Facuky of Ewacf Sciences, Tel-Aviv Univemiv, Tel-Aviv 69978, lsrael
A new pulsed flame photometer detector (PFPD) design is describedwith improved performance. Detection limits of 180 fg/s (sulfur), 7 fg/s (phosphorus), and 2 pg/s (niimgen) are demonstrated when 2 rms noise is considered as the detection limit The minimum detected amount of sulfurwas further reduced with a sulfurdoping method to about 30 fg/s. The factors affecting the sele&ty are analyzed in terms of operating the PFPD as a speci6c 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 296, which is dominated hy nondetector effects. The detector temperature effectwas studied and is presented. The ditrerence between light guide and lens optics is discussed. The column operation with hydrogen as a d e r 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 simultaneoususe ofdual 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 sulhu. The dual gate approach also provides up to an order of magnitude increase in the measurement dynamic range. Practical utilbtion of the PFPD is illustrated with the analysis of real-world samples, inclndmg thiophene in benzene, pesticides in a broccoli extract, and a sulfur-containing drug in human serum. The flame photometer detector (FPD) is a known and established detector for gas chromatography.'.z Recently, we introduced a new concept for the operation of FPD based on a pulsed flame instead of a continuous flame for the generation of flamechemil~minescence.3-~ This pulsed FPD (PFPD)was also coupled with a pulsed flame ionization detector (PFID) to form a combined pulsed flame photometric ionization detector (PFPID)." The PFPD is characterized by the additional dimension of a light emission time and the ability to separatein time the emission (1) Dressier, M.Selective Gos CkmmnfogmohicDefecton:Elsevier: Amsterdam 1986. (2) Farwell. S. 0.: Barinw, C. J. J. Chromologr. Sci. 1986. 24,483. (3) Amirav, A Pulsed Flame Detector Method and Apparatus. US. Patent 5153673; Israel Patent 95617: European and Japan Patent Appiications. (4) Atar. E.: Cheskis. S.: Amirav, A Anal. Cken. 1991.63, 2061. (5) Cheskis. S.; Alar, E.; Amirav. A Anal. Cken. 1993.65, 539. (6)Tzanani, N.: Amirav, A. A n d . a c n . 1995. 67.167.
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[email protected]/00 1995 American Chemical Satiety
Figure 1. Schematic diagram of the new PFPD design. (1) PFPD body; (2)GC-heated detector base; (3)central hydrogen-rich Hdair mixture tube leading to the combustor; (4) outer bypass Hdair mixture tube; (5) combustor holder (6) quartz combustor tube; (7) sapphire window; (E) light guide; (9) colored glass filter; (IO) photomultiplier; (11) spiral igniter light shield (12) heated wire igniter: (13) assemblv guiding rod in a guiding hole; (14) column.
of carbon species from that of sulfur and phosphorus, resulting in a considerable enhancement in the detection selectivity. In addition, the detection sensitivity is markedly improved thanks to (a) reduced flame background noise, which is filtered in time, (b) increased signal due to higher brightness of the pulsed flame, stemming from a small combustion cell volume and low combus tible gas flow rate,and (c) the use of broad-band color glass filters instead of interference filters. Moreover, the hydrogen and air gas consumption is greatly reduced, and the increased selectivity and sensitivity allow for the selective detection of nitrogen compounds via their HNO' flame chemiluminescence? In this paper we report on the results of our continued effort to improve the PFPD hardware, further characterize its behavior, and explore the various possibilitiesfor enhancing its performance through added time domain information. The PFPD is now available from Varian, and we hope this paper will help analysts to effectively use the commercial detector as well. THE NEW PFPD DESIGN A schematic diagram of the new PFPD is shown in Fire 1. The PFPD main body (1) is mounted on a GC detector base (2) provided by Varian (for the Varian PFPD) and clamped with two screws (not shown). A Varian 3600 GC was used for all the experiments described in this paper. Two hydrogedair gas mixtures, for which flow and composition are separately conAnaiyfimi Chemistry, Vol. 67, No. 18, September 15, 1995 3305
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