inhibited. Traces of CO result in partial inhibition. There is no reaction between the CO and Oz. Above 175" C. 0 2 and CO combine on the catalyst to form COz, but the reaction is not stoichiometric; a t various mixtures from approximately 1:99 to 99: 1 of CO to Oz, the products of the reaction include both CO and 0 2 as well as COS. Although we have found no reference specifically regarding the inhibition of the conversion of 0, to H 2 0 by CO when using a platinum catalyst in an excess of Hz, this behavior is consistent with known characteristics of catalytic Carbon reaction retardation (9). monoxide is a poison for platinum a t temperatures below 180' C. (6), and as a result, the series or parallel column (preceeded by the catalyst and CaCJ method of analysis cannot be used when both O2and CO are present. Oxygen and argon can be analyzed in the presence of carbon monoxide when COz is not of interest. It is necessary that CO and oxygen be separated prior to their passage through the catalyst-CaCz chamber. To accomplish this, the arrangement shown in Figure 3 has been utilized. A molecular sieve column is used to retard CO. The argon-oxygen mixture then passes into the catalyst chamber where the oxygen is converted to H20 and subsequently to acetylene in the CaC2
&NJ.
R4
Figure 3. Arrangement for analysis of samples containing CO and 0 2 but not COY
chamber. A short length of silica gel then separates the acetylene from the remaining gases under analysis. Since a molecular sieve column is utilized to effect the CO-osygen separation, carbon dioxide cannot be analyzed in this system a t room temperature. The order of elution in this system is helium, argon, nitrogen, methane, carbon monoxide, and oxygen (as C2H2). Assuming that the atmosphere in the laboratory contains the normal 0.94% argon, it was determined from calibration with pure argon, oxygen, and nitrogen that up to 2 ml. of O2 can be injected (at a hydrogen carrier flow of 35 ml. per minute) and conversion of 0 2 to HzO will be complete (within the limits of detection) in the absence of CO. Progressively larger injections sometimes result in incomplete con-
version to HZO, although normally the oxygen-hydrogen mixture will flash back into the carrier if insufficient H2 is present in the catalyst. With the glass catalyst chamber used, combustion of the 0 2 can be seen visually and always occurred within the first millimeter of the catalyst dispersion. Accordingly, very little catalyst need be used and this amount can be discarded when the CaCz is replaced. LITERATURE CITED
(1) Abel, K., ANAL. CHEM. 36, 954 11964). (2) Abel, K., deschmertzing, H., Ibid., 35, 1754 (1963). (3) Brenner, W., Cieplinski, E., Ann. N . Y . Acad. of Sci. 72, 705 (1959). (4) Duswalt. A. A.. Brandt. W. W.. ANAL. I - -
- - I
( 5 ) Greene,'S. A.,'Ibid.; 31, 480 (1959). (6) Griffith, R. H.,.Marsh, $1. D. F., "Contact Catalysis, p. 207, Oxford University Press, London, 1957. (7) Krejci, M., Tesarik,,,K., Janak, J.,
"Gas Chromatography, H. J. Noebels, R. F. Wall, N. Brenner, ed., Academic Press, New York 1961. (8) Lard, E. W., Horn, R. C., ANAL. CHEM.32, 878 (1960). (9) Psrlin, R. B., Wallenstein, M. D., Zwolinski, B. J., Eyring, H., in "Catalysis," P. H. Emmett, ed., Vol. 11, pp. 272-273. Reinhold. New York. 1955. (10) sundberg, 0. E., Maresh, C . , ANAL. CHEM.32, 274 (1960). (11) Vizard, G. S., Wynne, A., Chem. and Ind. 1959. 196.
An Improved Gas-Tight Micro Cross-Section Ionization Detector Kenneth Abel, Laboratory of Technical Development, National Heart Institute, Bethesda, Md.
Lovelock, Shoemake, and Zlatkis (3) have shown that the sensitivity of the cross-section ionization detector can be increased significantly by decreasing its internal volume. The micro volume detectors reported in the literature to the present time have design features which make them inconvenient to use because they do not allow for direct connection to metal columns, are not gas-tight, or do not provide satisfactory electrical connections. A dual-chamber micro crosssection detector was reported previously (1) for the analysis of gases produced by bacteria which did allow for direct column attachment but did not, have the simplicity, ease of modification, nor as satisfactory electrical connections as the detector described here; furthermore, it did require electrical shielding. The detector described below eliminates the problem of leakage at the detector, provides positive column connections (either solder or detachable metal connectors), provides an excellent, easily-detached electrical connection, is readily constructed of available materials and components, and does not require external shielding. All comECENTLY,
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ANALYTICAL CHEMISTRY
ponents are of Teflon, silicone rubber, and stainless steel, enabling the detector to be operated a t temperatures up to the tritium foil decomposition temperature of approximately 220' C. (The following sources'for specific components are listed for convenience and do not imply indorsement of these specific products by this laboratory: bulkhead coaxial mounts and coaxial cables, Microdot, Inc., Pasadena, Calif. ; conductive silicone rubber, Union Carbide Corp., New York 17, N.Y.; tritium titanate-coated foils, 100 to 150 mc. per sq. cm., Radiation Research Corp., Westbury, N. Y.; Teflon, Pennsylvania Fluorocarbon Co., Clifton Heights, Pa.) The sample chamber volume of one detector was 12 pl., thereby making the detector suitable for use with capillary columns without the necessity of utilizing a scavenger flow. Even smaller volumes appear to be feasible. The basic design of this detector is shown in Figure 1 in which one side of a dual-chamber version is shown in exploded view. The second chamber is identical. Column connections are brought in through the side with a
connecting hole drilled at right angles (as shown by the dotted lines) into the ionization chamber. A coaxial mount makes electrical connection by means of
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Figure 1. Exploded view of dual chamber micro cross-section detector
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a piece of compressilile conductive silicone rubber to a metal disk backing a tritium titanate-coated metal foil. Only one electrode is isolated, the second electrode being the grourtded base with the coaxial cable shielcl completing the circuit. This is arranged by utilizing the polarizing and base line current compensation circu t illustrated in Figure 2. It is this circuit which allows a simple gas-tight design with direct column connections to the base. The resistors and batterim comprising this circuit are shielded from extraneous electrical pickup by tieing enclosed in a metal box grounded to the coaxial shield. After being assembled, the detector is tightened, heated 1 o approximately 130" C. and then retightened causing the Teflon to flow into any irregularities. This results in a gas-tight cell and also decreases the chamb:r volume significantly (50y0 or more). Recycling the detector from 25' to 130" C. three times did not result ir gas leakage a t 1#5 p.s.i: Figure 3A illustrates a version with interchangeable tubing unions used as connectors to provide for direct attachment of '/16-inCh o.d., 1/8-inch o.d., or 1/4-inch 0.d. columns. Figure 3B utilizes a larger sample cham3er volume and a
scavenger flow inlet enabling the basic detector to be utilized in the electron capture mode. The dual chamber design can be utilized as a differential detector for dual column operation by utilizing two oppositely polarized circuits (for example, one +30 volts respective to ground and the other -30 volts), as was done by Boer (2)in his original dual chamber detector. We have, however, found it to be more useful for series column operation as is required in determinations of samples containing 02, Nz, and CO,. Although the detector has been operated a t temperatures to 220' C., detectors of much greater sensitivity are available for the higher boiling organic compound which requires these temperatures. The greater sensitivity of this detector for atmospheric gases has made it more suitable for room temperature operation in applications including blood gas analysis and microbiological gas evolution studies. For room temperature application no thermostating is required and the detector can be used without shielding of any nature.
B
A
Figure 3. Two versions of basic micro cross-section ionization detector A.
B.
Single chamber detector with interchangeable column connectors l a r g e chamber detector with scavenger inlet for electron capture mode
Because of the extremely small sample chamber, columns cannot be conditioned while attached to the detector, otherwise, an essentially direct electrical short invariably occurs across the Teflon spacer which provides an insulated path of only 0.2 to 0.4 mm. between the collector electrode and the base. The sensitivity and response characteristics of this detector make it suitable for Golay column operation. LITERATURE CITED
(1) Abel, K., deSchmertzing, H., Ari.4~. CHEM.35, 1754-6 (1963). ( 2 ) Boer, H., "Vapor Phase Chromatography, D. H. Desty, ed., p. 169, Academic Press, S e w York, 1957.
(3) Lovelock, J. E., Shoemake, G. R., Zlatkis, A,, ASAL. CHEM. 35, 460 (1963).
Densitometer for Quantitation of Stained Protein Fractions Separated Electrophoretically on Acrylamide Gel Slab Thomas G. Ferris, Robert E. Easterling, and Richard E. Budd, RADM Calver's Physical Chemistry Research Laboratory, Room 322, U. S. Naval Medical School, National Naval Medical Center, Bethesda, Md. EVELOPMENT of ac rylamide gel elecDtrophoresis by Raj,mond (5) greatly expanded the applictttion of electrophoresis as a research and clinical tool. It also created the need for a densitometer possessing gimeater versatility and sensitivity than those designed for scanning other media, such as paper strips. The design, fabrication, and method of operation of a recording densitometer for scanning and quantitation of serum protein fractions separated in acrylamide gel ,&reevaluated and discussed. EXPERIMEhTAL
Apparatus. The recording densitometer consists of three components. Amplifier-a Model 220 Optical Density Converter manufactured by
the Gilford Instrument Laboratories, Inc., of Oberlin, Ohio. Recorder-a Speedomax G with a 5.0-mv. sensitivity and a chart speed of 6 inches per minute, manufactured by the Leeds & Korthrup Co. of Philadelphia, Pa.; the recorder trace is integrated automatically by a ball and disk type of integrator. Scanner-component was built to our specifications. A three dimensional view is shown in Figure 1. The lamp housing contains a 15-candlepower tungsten lamp, a translucent light diffuser, a 606-mp interference filter, and a light slit 3/16 inch wide by '/2 inch long. The light slit is situated so that it lies directly above the scanning slit, d, during operation. The lamp housing is supported by parallel arms which permit i t t o be raised or lowered as necessary. The heavy black arrows indicate
the freedom of motion. The height of the lamp housing above the gel during scanning is controlled by an adjusting screw, c . Clearance between the housing and the surface of the gel is normally approximately inch. The scanning slit, d, is 0.005 inch wide by 0.25 inch long. The photocell is mounted in the cabinet directly below the scanning slit. During scanning the gel is supported in the gel holder, h, which consists of a dural metal frame l/s inch thick with inside dimensions 51/2 inches by 7 I i 2 inches. A sheet of thin optical glass is glued to the bottom of the frame to form a glass bottomed tray. The carriage, i, is made of l/r-inch dural and has inside dimensions 81/2 inches by 1l1/* inches. It is designed t o support the gel holder during scanning and is constructed so that the gel holder can be VOL. 36, NO. 4, APRIL 1964
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