Reference Standard for Mass Spectrometric Analysis of Nitrogen SIDNEY SOLOWAY Division of Nutrition and Physiology, Public Health Research Institute of the Cityuof New York,Inc.,’New York,N. Y.
N T H E course of routine mass spectronietric analyses of nitrogen variously enriched with XIS, it was necessary to
system of magnetic scanning. The analytical values Here reproducible with a probable error of 0.001 atom %, as shown in Table I. The difference of approximately 5% between the natural abundance of S’6 reported herein and that recently reported by Nier ( 2 ) may be attributed to differences in the scanning technique and in the arrangement of the slits in the ion gun. From Table I it can be seen that normal nitrogen samples prepared by three methods contain, within the precision of the author’s instrument, identical abundances of S1s. Samples prepared by the method described herein contain no detectable oxygen, which is a constant contaminant in samples of tank nitrogen as well as in samples prepared from ammonium sulfate ( 3 ) . The method has proved much more rapid and convenient in this laboratory than either of the other two methods, both for sweeping and as a standard. I n addition, the simple rernoval of oxygen from normal air ensures the absence of any fractionation of the nitrogen isotopes. Whereas no evidence of such fractionation in either tank nitrogen or ammonium sulfate has been encountered thus far, the occurrence of such fractionation in the preparation of these materials may becnine detectable as t tip precision of mass spectrometers increases.
have available a t all times a sample of standard nitrogen both for reference purposes and for sweeping after the analysis of highly enriched samples. Desirable features of such a standard would be: ( 1 ) constancy of isotopic composition, (2) ease of preparation, and (3) freedom from oxygen, because it has been found that oxygen disturbs the emission characteristics of tungsten filaments.
Table I.
Comparison of Composition of Samples of Nitrogen Prepared by Various M e a n s
Source s o . of N ‘6 of Nz Samples Atom’% Air Fieser’s soln. 4 0.382 * 0.001 5 0.382 t0.001 Commercial Nz (KHdrSO4 NaOBr 6 0 382 i:0,001
+
+
Oxygen,
Vol. % otw ineffective an addition agent. EXPERIMENTAL
Various amounts of pure metallic antimony were dissolved in 15 ml. of sulfuric acid (97%) by heating on the hot plate, and the solutions were cooled and diluted t o 125 ml. with water. Ten milliliters of hydrochloric acid (38%) and 10 ml. of hydrogen peroxide (3%) were added alld the so~utionswere boiled for 10 minutes to destroy the hydrogen peroxide. The solutions w r e
386
V O L U M E 23, NO. 2, F E B R U A R Y 1 9 5 1
387
diluted to 190 ml. and 5 grams of hydrouylamine hydrochloride were added. The solutions were then electrolyzed for 1 hour, using platinum gauze cathodes and platinum spiral anodes Two amperes (per sq. dm.) were used during the first 15 minutes and 1 ampere (per sq. dm.) for the last 45 minutes. The electroly-tes u erc stirred by air circulation. After the electrolysis tlir cathodes were immersed in water and alcohol, dried a t 105’ C. for 3 minutes, cooled, and weighed. The current used b j the author had an impressed voltage of 9 volts. The voltage across the electrodes was 2.8 volts. The results obtained for antimony are shown in Table I.
chlorine, hydrogen, and oxygen. However, tlic fact that excellent results were obtained indicates that the deposits were very pure. More than 0.4 gram of antimony should not be determined by the method; otherwise high results will be obtained. For instance, the result obtained by the author in electrolyzing 0.5000 gram of antimony was 0.5024 gram. In the sulfide method 0.2 gram of antimony is the masimum amount that can be handled (6). Copper, cadmium, tin, arsenic, le:id, bismuth, and silver interfere with the method, and when they are present, preliminary separations are necessary.
DISCUSSION
When metallic antiinony is dissolved in sulfuric acid, the antimony is in the antimonious state and must be oxidized with hydrogen peroxide. There is little danger of losing antimony by volatilization when the solution is boiled to destroy the hydrogen peroxide ( 4 ) . The amount of sulfuric acid and hydrochloric acid used in the method is not critic:tl. Good results were obtained using 10 t o 20 ml. of sulfuric x i d and 5 to 20 ml. of hydrochloric acid. The exact temperature used during tlie electrolysis is not important. Equally good results wrt, obtained using temperatures varying from room temper:tturc t o 80” C. Tests made with hydrogen sulfide after the electrolyses showed that no detectable amounts of antimony were left undeposited. It was not fwsible to test the deposits for possible occlusion of
LITERATURE CITED
(1) Classen, A., “Quantitative Analysis by Electrolysis,” p. 132, New York, John Wiley & Sons, 1913. (2) Diehl, H., “Electrochemical Analysis with Graded Cathode Potential Control,” p. 45. Columbus, Ohio. G. Frederick Smith Chemical Co., 1948. (3) Henz, F., Z.anorg. Chem., 37,31 (1903). (4) Hillebrand, W. F., and Lundell, G. E. F.,“Applied Inorganic Analysis,” p. 222, S e w York, John Wilcy & Sons, 1929. (5) Schoch, E. P., and Brown, D. 0...I. A m . Chum. Soc,. 38, 1660 (1916). (6) Treadwell, F. P., and Hall, W. T., “Analytical Chemistry,” Vol. TI, p. 213, Scw York, D. Van Nostrand Co., 1930. (7) Willard, H. H., and Diehl, H., “Advanced Quant,itative Analysis,” p. 348, New York, D. Van Sostrand Co., 1943. RECEIVED April 21, 19,513.
Versatile Paper Partition Chromatographic Apparatus ARNOLD J. SINGEK
AND
LEONAKII KENNER
Amni-i-dent, I n c . , Jersey City 6, iV. J .
’HE past few years have seen the increased use of -paper partition chromatography as both a qualitative and a quantitative analytiral micromethod. Coincident with increasing use of this method has been improvement of the apparatus in which the chromatogram is developed. Methods previously introduced
\
FIGURE
I
have embodied the principle of capillary descent (1, 4, 5, 8, 10) and capillary ascent ( 4 , 7 , 9, 11). Sumerous devices for the phase of solvent flow separation have been described, but these provide inadequate space (6, 7), have the paper strips inadequately supported (3, 9, 1 1 ) , or have both disadvantages ( 4 , 7). The authors have constructed a frame for rigid support of the paper a t both ends during the phase of solvent separation by capillary ascent. The frame has the following advantages in the use of paper partition chromatography as an analytical or separatory procedure: Up to 50 one-dimensional chromatographs can be developed a t one time; contamination of the strips by contact with each other or the walls of the apparatus is prevented; there is sufficient vapor space in the apparatus to reduce the effect of slight fluctuations in room temperature on the rate of flow of the developing liquid; the depth of the nick end of the paper in the liquid remains constant; the sample is a t a constant distance on the paper from the solvent; and the paper is supported tightly and vertirally, which eliminates variations in rate of flow due to slope of the paper Ftrips, The frnnie is constructed of 1 x 4 mni. strips of cold-rolled steel. Two strips 73 em. long mere bent into circles having an internal diameter of 22.5 em. and the ends were brazed together. These circles were then brazed to the ends of four strips 50 em. long a t 90” intervals around the circles. Two 3-crn. lerigthsof 4-mm. rod were brazed horizontally on thca top ring a t 180” and two flat “ears” 3 cm. wide, 6.5 cni. long, and 2 mm. thick were blazed on a t 90”. Four 3-cm. lengths of rod w r e brazed horizontally a t 90” intervals on the bottom ring. Thc RJdSwere used as stabilizers to orient the frame in the tank; the ears were used as handles and hangers. Friction tape was wound around both rings and pierced by 2-inch (5-cm.) steel pins pointing toward the center of the frame. The use of tape is suggested for greater flexibility of the apparatus. Similar frames of smaller diameter can be made to telescope nithin the outer frame. These can be used for additional strips and the frames can be removed selectively a t different tinw intervals.
