V O L U M E 28, NO. 7, J U L Y 1 9 5 6 (3) Bolts, D. F., ”Selected Topics in Modern Instrumental Analysis,” pp. 105-60. Prentice-Hall, New York, 1952. (4) Gahler, A. R . . ANAL.CHEM.26, 577 (1954). (5) Gillam, A. E., St,ern. E. 9.. “Introduction to Electronic Absorption Spectroscopy in Organic Chemistry,” pp. 185-94, Edward Arnold Ltd., London, 1954. (6) Gubler, C. J..S c i e m e 123, 87 (1956). (7) Herriot, R. >I.. “Symposium on Nutrition. The Physiological Role of Certain Vitamins and Trace Elements,” pp. 229-61, Johns Hopkins Press. Baltimore, 1953. (8) Kitson, R. E.. r l x . 4 ~CHEY. . 22, 664 (1950). (9) Lemberg, R., Lefrae, J. IT.,“Hematin Compounds and Bile
Pigments, Their Constitution, Metabolism and Function,” pp. 617-19. Interrcience, Kew Tork. 1949. (10) Lingane, J. J., Collat. J. W., Ax.4~.CHEM.22, 166 (1950). (11) McElroy, W . D.. Glass, B.. “Copper >letabolism,” pp. 274-315, Johns Hopkiiis Press, Baltimore, 1950.
1161 (12) hlellon, &G., !I. “Analytical Absorption Spectroscopy,” chap. 7 Wiley, New York, 1950. (13) Peterson, R. E., ANAL.CHEW25, 1337 (1953). Metals & Alloys 15, 245 (1942). (14) Silverthorn, R. W., Curtis, J. -4., (15) Smith, G. F., McCurdy, W. H., ANAL.CHEM.24, 371 (1952). (16) Smith, G. F., McCurdy, W. H., Diehl, H., Analyst 77, 418 (1952). (17) Tunnicliff, D. D., Brattain, R. R., Zumwalt, L. R., ANAL. CHEM.21, 890 (1949). (18) Underwood, A. L., Ibid.,25, 1910 (1953). (19) 5 anotti, A., Delachoux, A., “Iron bIetabolism and Its Clinical Significance,” Grune and Stratton, New York, 1949. (20) Wilkins, D. H., Smith, G. F., A n a l . Chim. Acta 9,538 (1953). RECEIVED for review February 23, 1956. Accepted April 25, 1956. Supported in part by a Grant-in-Aid from the Receiving Hospital Research Corp.
Ter Meulen Micromethod for Direct Determination of Oxygen R. NELSON SMITH, JACK DUFFIELD, ROBERT A. PIEROTTI, and JOHN MOO1 Chemistry Department, Pomona College, Claremont, Calif.
The ter Meulen method has been adapted to the direct determination of oxygen in organic compounds (sample size ranging from 3 to 10 mg.) and on the surfaces of various carbons containing 0.01 to 4.0Yo of oxygen (sample size ranging from 50 to 800 mg.). In a series of consecutive determinations, the time required for one determination is 15 minutes.
A
NUMBER of papers published in recent years indicate that
carbon-oxygen surface complexes are of interest to people working in a variety of research fields. I n order t o correlate a given property n-ith the xmoiint of carbon-oxygen surface complex, it is necessary to have a microanalytical method for the determination of the complex. Several methods have been proposed, but each one has some drawback. Oxygen can be determined satisfactorily by difference only if the oxygen content is rclntively high (12) and if the carbon, hydrogen, and ash content is known. With carbons of high sulfur or nitrogen content or containing relatively small amounts of oxygen, one must also k n o ~the sulfur and nitrogen content. The Vnterzaucher method ( 1 1 ) has been used (10) for carbon blacks, but i t is unsatisi’attory because the oxygen is evolved in a reasonable length of time only from those blacks which have a relatively high hydrogen content, and the presence of ash introduces an error with furnace blacks. PIIcDermot and Arne11 ( 2 ) determined the oxygen content of charcoal surfaces by passing hydrogen over the samples ( 5 to 7 grams) heated to 1000” C. and determining water, carbon dioxide, and carbon monoxide in t,he effluent gases. Difficulty x a s encountered with the large amount of water produced and n i t h incomplete conversion of the carbon monoxide to carbon dioxide in analysis. This paper describes a ter Meulen micromethod (4)as it was developed for applica,tion to some carbons used in this laboratory. The method works eqiiallj- n-ell with piire organic compounds. I n the ter Meulen method the sample is heated in a stream of hydrogen and any oxides of tnrbon rrhich are produced are catalytically hydrogenated t o methane and Tvater: the water is a measure of the oxygen in the original sample. Russell and Fulton ( 6 ) greatly improved the original method by replacing the platinized asbestos with platinized quartz for a cracking surface and by replacing the nickelized asbestos with a highly active thoriapromoted nickel methanation catalyst. The main disadvantages of the Russell-Fulton modification are the time needed for each analysis ( a t least 1 hour), the care needed t o vaporize the organic
compound in the first half hour, and the frequency of catalyst regeneration (usually every 10 t o 15 analyses, but as often as every four t o five analyses for certain compounds which carbonize the platinized quartz). I n many cases the sample size, 100 to 300 mg., may be excessively large. I n the present work the sample size has been reduced to 4 to 15 mg. of organic compound and the hydrogen has been specially purified to minimize the size of the blank. These changes reduce the analysis time t o 15 minutes, reduce the care needed for sample vaporization, and make reactivation of the catalyst a very infrequent operation. I n the case of the carbon samples, hydrogen removes only the carbon-oxygen surface complexes and practically all of the carbon remains at the end of the analysis. Organic compounds are generally completely vaporized. EXPERIMENTAL
One black and two charcoals were used in this work. A partially graphitized carbon black (supplied through the courtesy of the Godfrey L. Cabot Co.) was made by heating Spheron Grade 6 ( a medium processing channel black) to approximately 3000’ in an electric furnace. The surface area is about 80 square meters per gram and its ash content is about Graphon.
0.0257@ Su-60. A sugar charcoal of extremely low ash content mas
prepared, starting with confectioner’s AA sugar furnished through the courtesy of the California and Hawaiian Sugar Refining Corp. This sugar was used because it had an ash content of 0.0008%. After activation (9) this charcoal had a B E T area of 1020 square meters per gram, using ethyl chloride, and its ash content was less than 0.005%. B. An activated commercial nut charcoal, de-ashed with hydrochloric acid in a Soxhlet extractor, dried and heated to 1000” in vacuo. The B E T surface area is 1050 square meters per gram and its ash content is about 0.2%. Analytical Apparatus and Procedure. The reduction apparatus for the carbon-oxygen complexes consists of a clear quartz tuhe with dimensions standard for combustion tubes used in ordinarv carbon-hydrogen microdetermination. For carbon samples whose size must be increased because of the small amount of oxygen present, the first 18 em. of the reduction tube is replaced Fith a piece of quartz of larger diameter. I n this work a piece 20 mm. in outside diameter was used. This tube is filled, starting a t the exit end, with about 3 em. of silver wool, about 8 em. of nickelthoria catalyst (about 6 grams), and finally about 13 cm. of platinized quartz (20 mesh). The nickel-thoria catalyst and platinized quartz are prepared as described by Russell and Fulton (6). A standard absorption tube filled with Anhydrone is connected t o the exit end of the reduction tube, and a flowmeter and guard tube are connected t o the exit end of the absorption tube. The nickel-thoria section of the reduction tube is fittet with an electric furnace and adjusted for running a t 350’ (400
1162
ANALYTICAL CHEMISTRY
for initial reduction or regeneration). The platinized quoart2 section is fitted with an electric furnace for running a t 1000 If a source of special high purity hydrogen is available this is connected to the side arm of the reduction tube, as in ordinary combustion analysis. In this work ordinary tank hydrogen was used and purified, as used, by passing it through a series of tubes arranged in the following order: Deoxo Purifier (Baker 8t Co. palladium catalyst) ; a 16-em. electrically heated (350') tube filled in the first half with platinized quartz and in the second half with nickel-thoria catalyst; a 16-em. tube filled in thirds with Anhydrone, Ascarite, and then with Anhydrone again: and finally a 50-em. tube filled in thirds with Anhydrone, Ascarite, and Anhydrone. The tubes used for this purpose were made from pieces of 11-mm. Corning 172 combustion tube. There appears to be no need for the nickel-thoria catalyst tube, but the tank hydrogen used in this work contained a trace of some hydrocarbon which, without prior removal, made the blanks much too high. The short Anhydrone-Ascarite tube needs relatively frequent replacement, and the long tube merely serves as an extra precaution. In order to create a nitrogen atmosphere around the mouth of the reduction tube, a 6.5-cm. funnel is placed beneath the mouth of the tube and a strong current of nitrogen is passed through it just before the sample is introduced to (or the boat removed from) the hydrogen stream. This procedure prevents "flashbacks," which otherwise occur rather easily. All samples are introduced from a weighing piggy filled with nitrogen. To facilitate the transference and to prevent the influx of air, the weighing piggy and reduction tube are of the same diameter, with ends ground square. With the end of the piggy butted against the reduction tube, the boat is pushed or pulled from one to the other with a suitable glass rod. Proper operation of the reduction train is checked nith pure benzoic acid (Parr calorific grade) before each day's rum.
.
The following preparative procedure was adopted for the oxygen determinations in the carbon samples, in order to remove physically adsorbed moisture and to prevent take-up of oxygen from the air. The carbon samples, in porcelain boats, were outgassed a t 110" in vacuo (with continuous pumping) for 12 hours, cooled to room temperature in vacuo, surrounded with nitrogen a t 1 atm., transferred to weighing piggies in a stream of nitrogen gas, stoppered, and then weighed. After analysis, the boat was again weighed in the same piggy with nitrogen; the sample weight was obtained by difference. The organic compounds (contained in platinum boats) were weighed in weighing piggies thoroughly flushed out with nitrogen. All weighings were done in the presence of polonium to eliminate error due to static charges. Even when not in use the nickel-thoria catalyst furnaces were kept a t 350', and a hydrogen flow of about 5 cc. per minute was maintained. About 15 minutes before making determinations, the platinized quartz section was raised to about IOOO", the Anhydrone absorption tube was put in place, and the hydrogen flow rate was adjusted to 75 cc. per minute. A sample, in a boat, was weighed in a weighing piggy in a nitrogen atmosphere (carbon samples were weighed as in the preceding paragraph). The absorption tube was removed, flushed with 250 cc. of dry air, \?
