An Easily Constructed Alkali Flame Ionization Detector W. H. Stewart Sun Oil Company, Marcus Hook, Pa. 19061
ALKALIFLAME IONIZATION DETECTORS (AFID) are useful accessories in flame ionization detector (FID) gas chromatographs (GC) for obtaining enhanced response to nitrogen, phosphorus, sulfur, and halogenated compounds. An A F I D has been described ( I ) which can be constructed in the laboratory and fitted on many commercial G C units. This version of the detector is difficult to make, however, because it requires manipulating a small, fragile piece of fused salt. We describe here a version of the A F I D which is extremely easy to construct. Several detectors can be prepared a t one time and no cutting, sanding, or shaping is required. The detector is rugged and can be handled without fear of breaking. The detector consists of a l/ls-inch stainless steel front ferrule (Swagelok Part No. 103-1-316) filled with the desired salt, in our case K2S04,KBr, R b S 0 4 , or a 1 : 1 mixture of RbSO,: KBr. The salt is pressed into the front ferrule by using a inch die (Spex Industries KBr Die MK3) a t 16,000 psi for about twenty minutes. No problems were experienced in pressing the above mentioned salts. As many as eleven detectors can be pressed at one time, depending upon how the front ferrules are arranged in the die. The only alignment precaution necessary is to ensure that the front ferrules are set flat on the die face. Sufficient salt should be used in the die to completely cover the front ferrules by a n additional inch. Once pressed, the salt is bored to 0.020 inch (No. 76 drill bit) for positive response mode or 0.040 inch (No. 59 drill bit) for negative response mode (2) and counterbored (No. 53 drill bit) to fit over the jet tip in the F I D (Figure 1). The detectors were operative after at least five days in the G C but were usually replaced at this time with no visual degradation and minimal weight loss. Because eleven detectors can be prepared at one time and it takes only a few minutes to drill them out, this replacement frequency is not a problem. Although all work was performed on a Perkin-Elmer Model 900 GC, the front ferrule will also fit on the jet tip of a Hewlett-Packard Model 5750. Larger front ferrules could easily be used in gas chromatographs with larger jet assemblies. The Perkin-Elmer Model 900 G C used was not modified in any respect except the addition of the alkali salt on the flame tip. Polarization voltage, electrode spacing, and flow pattern of the ion chamber were all standard conditions. Optimum operating conditions for the detection of nitrogen compounds o n this Model 900 with a 6-foot X l/B-inch a d . stainless steel column packed with 1 0 % silicon gum rubber SE-30 on 60-80 GAWDMCS 900 were 208 ml/min of air and 39 ml/min of hydrogen with a helium carrier gas flow of 30 ml/minute. The injector and detector block temperatures were maintained at 350 "C while the column was temperature programmed from 150 to 225 "C at 32"/minute with a one minute delay. A six-component mixture (Figure 2) containing 16.3 weight per cent benzene, 16.2 % trimethyl-pyridine, 1 7 . 5 x dichlorobenzene, 15.8 ethyl benzoate, 18.0% normal tridecane, and 16.2 % azobenzene was chromatographed with and without a KBr AFID in the gas chromatograph. Figure 2 clearly shows that the AFID selectivity discriminates against
(1) D. A . Craven. ANAL.CHEW,42, 1679 (1970). (2) W. A . Aue and K. 0.Crerhardt, J. Clzromatogr., 52, 47 (1970).
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Figure 1. Schematic diagram of AFID detector
a. WITH CONVENTIONAL FID
b.
WITH AFID
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Figure 2. Analysis of six-component mixture
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Figure 3. Analysis of 99.9989 mole per cent nitrogen and 0.0011 mole per cent hydrogen sulfide mixture with AFID ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
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non-nitrogenous compounds while also providing some enhancement of the nitrogen compounds. The negative peak for the chlorinated hydrocarbon agrees with the results of Aue and Lakota (3) while the negative peaks for the other three compounds are due to a disturbance of the detector. I n the sulfur mode, it is possible to detect compounds such as hydrogen sulfide and carbon disulfide which give no response with a standard FID. Optimum operating conditions for the detection of hydrogen sulfide o n this Model 900 with a 5-foot X I/s-inch 0.d. stainless steel Porapak R column a t 50 “C isothermal were 240 ml/min of air and 70 ml/min of hydrogen with a helium carrier gas flow of 50 ml/min. The injector and detector block temperatures were maintained a t 100 O C . A sample of 0.0011 mole per cent hydrogen sulfide in nitrogen was detected (Figure 3) using a K 2 S 0 4AFID bored to 0.040 inch. Performance characteristics of the alkali salt filled front ferrules are in good agreement with those reported by Kar(3) W. A. Aue and S. Lakota, J . Chromatogr., 44,412 (1969).
men (4), Aue (3, and Craven ( I ) for the nitrogen mode and Dressler and Janfik (6) in the sulfur mode. The ease of construction and ruggedness of this A F I D made it practical to convert any FID into an AFID and make this technique available to more laboratories. The simple manner of construction also makes it practical t o study the effects of different salts in the operation of the AFID. ACKNOWLEDGMENT
The author wishes t o thank D. M. Schoengold for invaluable assistance.
RECEIVED for review December 16, 1971. Accepted March 1, 1972. (4) A. Karmen, Science, 7, 541 (1967). (5) W. A. Aue, C. W. Gehrke, C. D. Ruyle, D. L. Stalling, and R. C. Tindle, J. Gas Chromatogr., 5, 381 (1967). (6) M. Dressler and J. JanBk, J. Chromatogr. Sci., 7, 451 (1969).
Novel Type of Hydrogenator P. G . Simmonds and C. F. Smith Space Sciences Division,Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Calif. 91103 VAPORPHASE HYDROGENATION of unsaturated organic compounds is of general interest for structure determination in organic chemistry. A convenient technique for performing analytical hydrogenation is t o place a reactor, containing a hydrogenation catalyst, in series with a gas chromatographic column (1, 2). This method of micro vapor phase hydrogenation has been demonstrated to be particularly useful for determining the olefin content of mixtures of hydrocarbons (3)and fatty acids (4-6). A minor limitation of the technique is that certain compounds, such as aldehydes, halides, and sulfides, may undergo some hydrogenolysis to form the corresponding saturated hydrocarbons. During a recent study (7) of a palladium-hydrogen separator for interfacing a gas chromatograph-mass spectrometer system, it was observed, not unexpectedly, that certain unsaturated compounds were reduced during passage through the narrow-bore palladium-silver tubing which was used to construct the separator. In general, hydrogenation was restricted to a,P-conjugated double bonds, such as in unsaturated aldehydes, ketones, nitriles, and esters. Monoolefinic compounds, such as alkenes, showed less than 5z reduction to the corresponding alkanes. However, if conditions are arranged so that hydrogen permeates from a high (1) M. Beroza, and M. N. Inscoe, in “Ancillary Techniques of Gas Chromatography,” L, S. Ettre and W. H. McFadden, Ed., Wiley-Interscience, New York, N.Y., 1969, Chap. 4, p 89. ( 2 ) M. Beroza, and R. Sarmiento, ANAL.CHEM., 38,1042 (1966). (3) R. Rowan, Jr., ibid., 33,658 (1961). (4) J. H. Dutton andT. L. Mounts, J. Cutul., 3,363 (1964). 37,641 (1965). (5) T. L. Mounts and J. H. Dutton, ANAL.CHEM., (6) H. J. Dutton, in “Advances in Tracer Methodology,” Vol. 2, S. Rothchild, Ed., Plenum Press, New York, N.Y., 1965, pp 123-34. (7) P. G. Simmonds, G. R. Shoemake, and J. E. Lovelock, ANAL. CHEM., 42,881 (1970).
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ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
pressure source into the interior of a heated palladium alloy tube containing unsaturated compounds, we have observed that quantitative reduction of both conjugated and unconjugated olefins can take place. Wahlin (8, 9) has previously described the hydrogenation of cyclohexene in a palladiumsilver tube in which the hydrogen was generated from the electrolysis of water by making the tube cathodic in a n electrochemical cell. The present paper describes the investigation of a palladium-silver tube as a catalytic reactor for the vapor phase hydrogenation of unsaturated carbon-carbon bonds in a variety of organic compounds. The device is simple to construct from a n appropriate length of palladium-silver tubing and may be used for both continuous and batch hydrogenations. As a batch hydrogenator, it may also be used as a component of the gas chromatographic system and in this respect its performance is similar to that of the packed catalyst reactor. However, it is not necessary to change the carrier gas to hydrogen, since in practice hydrogen diffuses from a n external supply into the interior of the catalytic tube where it rapidly mixes with any convenient carrier gas. Furthermore, in contrast to the packed catalyst hydrogenator, the palladium tube device does not cause hydrogenolysis of sensitive aldehyde groups. Unfortunately with the present palladiumsilver alloy, there is some reaction with both halogen- and sulfur-containing compounds; presumably due to the formation of silver halides and sulfides. However, it is possible that this difficulty may be overcome by the use of other palladium alloys which d o not react so readily with these compounds (IO). (8) H. B. Wahlin and V. 0. Naumann, J. Appl. Phys., 24,42 (1953). (9) H. B. Wahlin, U.S. Patent 2,749,293 (1956). (10) D. L. McKinley, U.S. Patent 3,359,845 (1967).
