roughness factors obtained for the platinum gauze and glass tubing, show the reliability of the dynamic method. A value of 0.38 sq. meter per gram is reported in the literature (4) for the specific surface area of pumice. Since the glass sample tube (3-mm. i.d.) had appreciable surface area compared to the platinum gauze, it was necessary to correct for the contribution made by the glass sample tube when measuring the surface area of the platinum gauze; the value given in Table I represents the corrected value. The geometrical surface area for the 3-mil platinum wire used in the gauze was 25.5 sq. em. per gram. The roughness factor obtained for the platinum gauze is consistent with the value of 2.1, which has been reported for smooth platinum metal ( 3 ) . A linear relationship vias obtained between the calculated geometrical surfaces and the adsorbed krypton volumes for various depths of immersion of the glass sample tube. Incremental surface areas of 6 sq. cm. were easily detected. The calculated roughness factor for the glass sample tube given in Table I agrees reasonably well with the value of 1.7 which mas determined from Rosenberg’s data ( I S ) . I n the krypton measurements for low surface area materials. it was necessary to purify the grade A h(,lium carrier gas further. An activatzd carbon trap immersed in liquid nitrogen eliminated most of the interference due to trace
impurities in the helium. Hydrogen caused the most interference; it could easily be detected because it sorbed at a different time and its peak \vas in the opposite direction. At most, the interference due t o hydrogen was estimated to be less than 5y0 of the measured surface area. The use of the dynamic method for krypton measurements eliminates the necessity for making the thermomolecular flow corrections as described by Rosenberg ( I S ) . This simplification of the dynamic over the static method is a distinct advantage, in both time and instrument complexity. CHEMISORPTION MEASUREMENTS
The dynamic method was found useful for high temperature sorption studies on solid catalysts-for example, sorption of hjdrogen by iron oxide a t 300’ C. The iron oxide sample was outgassed by passing helium through the system overnight at 300’ C. The sample was then bypassed through use of three-way valves and hydrogen added to the helium stream. When the gas stream vias rcdirectrd over the sample, a sharp adsorption peak occurred, indicating a fast chemisorption of hydrogen. Thc area under the adsorption peak, after the dead space correction, gave the volume of hydrogen adsorbed. The dead space in the sample tube was determined from a blank run with an empty tube, with a correction for the volume of catalyst sample. Catalysts
R-hich wcre less stable toward reduction with hydrogen than iron oxide showed extensive tailing of the adsorption peak. Alternate methods involving frontal analysis have been used by other workers (6, 6) t o obtain similar data. From such data Cremer and Huber (5) calculated heats of adsorption of various gases on catalysts a t elevated temperatures. LITERATURE CITED
(1).Barr, W. E., Anhorn, V. J., “Scien-
tific and Industrial Glass Blowing and Laboratory Techniques,” pp. 257-83, Instruments Publishing Co., Pittsburgh, Pa., 1949. (2) Brunauer, Stephftp, “Adsorption of Gases and Vapors, Vol. I, “Physical Adsorption,” p. 151, Princeton Universitv Press. Princeton. N. J.. 1943. (3) Ibid:, p. 284. (4) Ibid., p. 298. (5) Cremer, E., Huber, H., Angew. Chem. 73, 461 (1961). (6) Eberlg, P. E., Jr., J . Phys. Chem. 65, 1261 (1961). ( 7 ) Emmett, P. H., Brunauer, Stephen, J . Am. Chem. SOC.59, 1553 (1937). (8) Lange, N. A., “Handbook of Chemistry,” 5th ed., p. 1416, Handbook Publishers, Pandusky, Ohio, 1944. (9) Loebenstein, W. V., Deitz, V. R., J . Research -Vatl. Bur. Standards 46, 51
(1951). (10) Meihuizen, J. J., Crommelin, C. A., Phusica Physica 4. 4 , 1 (1937). (11) Gelsen; Nelsen, F. AI., Eggertsen, F. T., A N ~ LCHEII. . 30, 1387 (1958). (12) Perkin-Elmer Corp., Xorwalk, Conn., “Instructions, Perkin -,,Elmer - Shell Model 212 Sorptometer, 1961. (13) Rosenberg, A A. J., J . A m . Chem. SOC. 7 8 , 2929 (1956) (1956).
Beilstein Flame Method of Detection of Organohalogen Compounds Emerging from a Gas Chromatograph
F.
A. Gunther, R. C. Blinn, and D. E. Ott, University of California Citrus Research Center and Agricultural Experiment Station, Riverside, Calif.
0
of the greatest wcaknesws of gas chromatography is the nonspecific nature of the response. This weakness is not aln-ays realized or properly appreciated. A gas chromatogram is merely a sequence of more or less symmetrical peaks forwhich assumptions are too often made as to their identity. Since most of the currently available detectors cannot make specific identifications, i t is only reasonable that supporting use should be made of accepted chemical and physical analytical methods (9). One such method utilizes a simple device, based on the Beilstein test, to detect those compounds which contain organically bound chlorine or bromine. This device leads all or a portion of the effluent from a gas chromatographic column through a copper-screen thimble held in the outer cone of a cool Bunsen burner flameNE
302
ANALYTICAL CHEMISTRY
emergence of an organohalogen compound is signaled by the immediate appearance of an intense grecn flame. This idea is not new. The classic Beilstein test consists of a clean copper wire dipped into a compound and held in a hot flame as a color test for the presence or absence of halogen ( I ) . Numerous modifications of this test to achieve specificity and sensitivity have been described (3-5). Quantitative applications in the form of flame photometry have also been reported (6, 7 ) . Its qualitative and suggested quantitative application with gas chromatography was described in 1959 by Dubois and Monkman (9, 8 ) , with several hundred micrograms of chlorinated materials required for detection in their apparatus, in which the column effluent was mixed with natural gas in the barrel of the burner. With present
techniques, in which the column effluent is introduced through a copper screen thimble directly into a cool flame, sensitivity of the test by visual observation of the flame in a lighted room is less than 5 Mg. of organically bound chlorine from an elution peak lasting 30 seconds, or 0.167 pg. of chloride per second. Enhanced sensitivity may be achieved by observation of the flame through a n ultraviolet filter in a darkened environment, by simple spectrophotometric means, or by flame miniaturization against a dark gray or black background. The upper limit, which does not simultaneously overload this flame detector so as t o result in apparent flame ‘[tailing”, is about 1.5 mg. over a n elution period of 30 seconds, or 50 pg. per second. The test responds to organic compounds containing chlorine, bromine,
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Figure 1. Details of incorporation ofthe halide detector on an instrument to allow a 7 cell to b e constant portion of the effluent gas flow f tested. The copper screen is 30 mesh
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iodine, cyanide, thiocyanate, and certain other groups which degrade to cyanide in the flame (S,5,10). Figure 1 shows a detailed sketch of the Beilstein flame detector &s installed to respond to only a Bortion of the flow from the thermal-conductivity ccll. For greater sensitivity, all of the flow from the ccll may he used. Figure 2 represents a plot of boiling point us. elution time of various halogenated compounds from a six-foot Apiezon-J column at 150' C . t o illustrate use of this test. Peak maxima are represented by circles; the length of each lower bar represents the time between appearance and disappearance of the green flame; each middle bar represents the time abscissa of the thermal-conductivity peak by triangulation; and each upper bar represents
the width of the recorded peak a t base line inflections. To utilize the flame in a quantitative manner, reference can be made to that area, under a thermal-conductivity plot which coincides with the appearance and disappearance of the green flame. By using the flame as an indicator of emergence of organohalogen compound, and hy splitting the stream and trapping a portion of the eluent, the method affords a clean organohalogen fraction for more positive identification by infrared or other suitable means. LITERATURE CITED
(1) Beilstein, F. X., Ber. 5,620 (1872). (2) Duhois, L., Mykman, J. L., "Gas Chromatography, Noehels, Wall, Brenner, eds., p. 237, Academic Press, New York, 1961.
- ~ " -" ~ "." ~
Organic Analysia," Elsevier, Amsterdam, 1956. (4) Hayman, D. F., IND.ENG. CHEM., ANAL.ED. 11,470 (1939). (5) Jurany, E.,Mzkrochm. Acta 1, 134 ll l_ lr_l_5, _5 ~
(6) M m h , G. E., A19pl. Speet7oscopy 12, 113 (1958). (7) Maruguma, M., 5:,no, S., Bull. Chem. Soe. Japan 32,480I(1959). (8) Monkman, J. L.l.DphpisL.L:> 'Gas Chromatography," Noebels, Wall, menner, eds., p. 333, Academic Press, New York, 1961. (9) Monkman, J. L., Dept. of National
Health and Welfare. Ottawa. Canada. ~mmnnication, Novemner 1961.
(10) von Alph en,, J., Rec. traa. chim. 42,
567 (1933).
PAPERNo. 13&, V U Y Z I U ~ V I UULWUZ Citrus Research Center and Agricultural Experiment Station, Riverside, Calif. Presented before the Divis/on of Agricultural and Food Chemistry, 139th Meeting, ACS, St. Louis, Mo., March
Use o# Sample Rotators for Fluorescence Analysis of Light Elemeint s in Cement Raw Mix A. A. Tabikh, California Portland Cement Ca., Colton, Calif.
x-
RAY FLUORESCENCE is
being used . . by a n increasing number of laboratories for the analysis of Fe, Ca, Si, and AI in cement raw mix. However, high precision and accuracy oftcn have heen lacking unless there was some pretreab ment of the specimen. A few techniques of sample preparation have been proposed (1,S, 4 ) which would improve the results. Drawbacks to these for rapid control analysis are such factors as lengthy preparation require-
ments, necessity for rcpeated weighiugs, and loss in fluorescence intensity because of sample dilution. Generally, x-ray analysis of raw mix becomes a practical method only if it is possible to analyze specimens after a minimum of handling. In dry processing, raw mix is a powder, 85 to 90% of which passes through 200-mesh sieve. Since the material is a composite of a number of minerals varying in hardness and other physical propertics, it is
extremely difficult to produce a uniform particle size by grinding. When the surface of a raw mix sample pressed for analysis is examined under a microscope, the variations are evident in several respects. Particle size, crystallinity, orientation, and the mineralogical identity of large grains all make the surface entirely heteropolymorphic. A homogeneous surface is preferable if a fair degree of precision is to be attained, because for the analysis of light eleVOL. 34, NO. 2, FEBRUARY 1962
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