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
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