ANALYTICAL CHEMISTRY
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from routine analyses of shale oil and petroleum products. Lower precision is to be expected when highly volatile aamplw are anslyaed. Accuracies attained with this procedure are indicated by values given in Table VI. LITERATURE CITED
(1) Ball, J. s..and Van hfeter, Robin, ANAL.C H m f . , 23,1632 (1951). (2) Bradstreet, R. B., Chern. Rez,6.,27,331-50 (1940).
Gunning, J. W., 2. anal. Chem., 28, 188 (1899). (4) Kirk, L., CHEM., 354-8 (1*50). (5) Ogg. C. L.,and Willits, C. O., J . dssoc. Ofi. Agr. Chemisk, 33, 100-3,179-88 (1950). (6) Osborn, R.A., and Krasnitr, A , Ibid., 17,339 (1934). (7) Osborii, R. A., and Wilkie, J. B., Ibid., 18, 604 (1935). ( 8 ) White, L.M., and Long, M. C., ANAL.CHEM.,23,363-5 (1951). (9) Wilfarth, H., Chem. Zentr., 56,17,113 (1885). (3)
22i
RFCFJVED March 5, 1951.
(Determination of Nitrogen in Shale Oil and Petroleum)
EVALUATION OF DUMAS PROCEDURES BY MASS SPECTROMETRY ROBIN VAN METER, C. W. BAILEY, AND E. C. BRODIE' CT. S . Bureau of Mines, Laramie, Wyo. Attempts to determine nitrogen in shale oil or its fractions by the Dumas micromethod generally resulted in high and variable results. The mass spectrometer was used to analyze the gases in the nitrometer. The presence of hydrocarbons and nitric oxide indicated that proper techniques were not being used in the combustion. The ability to detect
A
N EXCHANGE program to determine the nitrogen content of certain shale oils was discussed in a preceding paper ( 1 ) . The Dumas analysis results reported for a typical sample range from 1.45 to 2.04%. The scattered distribution of these values indicates that many of the laboratories urgently need a means of evaluating this analytical method. Mass spectrometer analyses of gases produced in the Dumas micromethod (3) have been helpful in diagnosing errors in technique and errors due to the use of insufficiently reactive copper oxide and metallic copper. The analyses have aided in the orderly elimination of the more serious errors by showing the effect of changes in technique and reagents. They have also permitted the salvage of otherwise valueless determinations when corrections for extraneous materials have been applied. .41though the Bureau of Mines laboratories have applied mass spectrometer corrections to Dumas microdeterminations only, they should be equally advantageous for verifying semimicroand macrodeterminations. The mass spectrometer has been used with the Dumas method by Hindin and Groase (g) in a different procedure that employs neon as an internal standard.
extraneous gases and to identify them provides a tool by which the effectiveness of the procedures may be tested. Revision of the procedure until only nitrogen is collected in the nitrometer results in good analyses. In some instances corrections may be applied to nitrometer readings containing extraneous gases, 80 that acceptable results are obtained.
moisture is present. Remove this by absorption in an anhydrous magnesium perchlorate drying tube during introduction into the inlet system. RESULTS
Table I shows the gases that have been found in the nitrometer and their range of concentrations. The hydrocarbon gas is
-t I
l
95mm
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1 I
T
50 m m
l
I
PROCEDURE
Standard Dumss micromethod nitrometers are equipped with a small funnel sealed above the stopcock. To facilitate the transfer of gas into the mass spectrometer, cut off this funnel just above the stopcock and seal a glass interjoint connection in its place. Figure 1 shows the result of this simple alteration. As the volume et nitrometer gas is 80 small (generally approximately 0.2 ml.), the usual method of introducing a gas to the mass spectrometer cannot be used. Figure 2 is a schematic drawing of the portion of the inlet system used in a Consolidated mas3 spectrometer (Model 21-102). Instead of measuring the preasure of the gas in the metering volume, introduce the gas through volume C into the large sample bottle, A , to a pressure of about 0.07 mm. as measured on the Pirani gage. This pressure gives the most satisfactory peak heights for calculations. As the gas is collected over a saturated solution of potassium hydroxide, considerable 1
Present address, University of Arizona. Tucson, Aria.
UNALTERED DUMAS BELOW SEAL
MICRONITROMETER
Figure 1. Modification of Dumas Micromethod Nitrometer for Introducing Collected Gas into the Mass Spectrometer Scale. One half actual size Material. Borosilicate glass throughout
Table I.
a b
Compounds Found in Dumas Nitrometer G a s and Their Range of Concentrations
Compound Max., % ' Min., % ' 0.0 81.3'' Hydrocarbons 18.6 100 Nitrogen 0.0 4.0 Nitric orideb 0.0 0.3 Carbon dioxide Methane content in this inetance was 80.8%. The presence of nitric oxide was confirmed by chemical means.
V O L U M E 23, NO. 11, N O V E M B E R 1 9 5 1
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mostly methane, and the relatively small number of components makes the calculations rather simple. Traces of air occasionally enter the inlet system of the spectrometer during transfer of the sample. The analysis is reported on an air-free basis, calculated from the oxygen content of the nitrometer gas.
Table 11.
Dumas Microanalyses of Shale Oil and Fractions Nitrogen, % Uncorrected Corrected 2.0 1.86 1,9
