CONCLUSIONS
The GLC oxidation technique offers a means of conveniently oxidizing asphalt? for further study by inverse GLC without physically disturbing the sample. Close control over a wide range of oxidation temperatures is possible with reproducible results. Comparison of the oxidation-inverse GLC data with results of accelerated weathering tests on a limited number of asphalts shows that the GLC technique may be useful in predicting asphalt durability.
The technique, although developed for asphalt. should find general application by analysts for a wide variety of high molecular weight organic materials where changes upon oxidation are important. LITERATURE CITED
(1) Davis, T. C., Petersen, J. C., Highway Res. Record No. 134 (1966). (2) Davis, T. C., Petersen, J. C., Haines, IT7. E., AN.4L. CHEM. 38, 241 (1966). (3) Greenfeld, S. H., Wright, J. R., Mater. Res. Std. 2 (9) 738-45 (1962).
(4).Greenfeld, S.H., Private communication, i'iational Bureau of Standards, Washington, D. C., January 1965. T. C. Davis J. C. PETERSEX
Laramie Petroleum Research Center Bureau of Mines, U. S. Dept. of Interior Laramie, Wyo. THEwork upon which this report is based was done under a cooperative agreement betmeen the Bureau of Mines, U. ,S. Dept. of the Interior, and the University of Wyoming. Reference to specific brand names is made for identification only and does not imply endorsement by the Bureau of Mines.
apid Determination of otal Nitrogen Plus Oxygen Cornpounds in Heavy Petroseu Distillates by Adsorption Chromatography SIR: Compounds containing nitrogen and/or oxygen can account for as niuch as 20% of virgin or cracked petroleum samples boiling between 400' and 1000' F. The compositional analysis of such samples by mass spectrometry (1) or other means generally ignores the presence of these heterocompounds, and directly-determined compound typese+, hydrocarbons and sulfur compounds-are simply normalized to lOOyo. A rapid procedure for determining the sum of these oxygen and nitrogen heterocompounds in petroleum distillates would be of general value in the compositional analysis of heavy petroleum samples, and might have specific application to certain aspects of petroleum processing and use where this group of compounds plays a unique role. The present method was developed primarily for use in conjunction with a recently reported ( 2 ) direct mass spectrometric method for the analysis of various compound types in heavy petroleum distillates. -
,
n
MAXIMUM %W H E T E R O COMPOUND§
Figure 1 . Nitrogen plus oxygen heterocompounds by routine procedure vs. maximum possible heterocompound eontents
0 Cracked
samples Virgin sampler Blends of cracked and virgin streams
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ANALYTICAL CHEMISTRY
9 5 % BOILING T E M P E R A T U R E *
Figure 2. Estimation of average heterocompounds molecular weight from sample distillation data *e.g., Am. SOC. Testing Materials, ASTM Standards on Petroleum Products and Lubricants, "Distillation of Gas Oils and Similar Distillate Fuel Oils D-158," (1 9 6 0 ) p. 87
The basis of the present procedure is the adsorption chromatographic separation over alumina of the heterocompounds from other sample components. The method is quite similar to the separation of heterocompounds in a recently described ( 3 ) method for more detailed petroleum separations, but is simpler and more rapid (about man hour per sample, us. 16 man hours per sample by the previous method). As described previously ( 3 ) ,the accuracy of the present procedure can be evaluated either from the comparison of "maximum total heterocompounds" (calculated from elemental analysis and molecular weight data) with experimental values for total heterocompounds, or from recoveries of oxygen and nitrogen in the separated heteroconipound fraction. The present experimental procedure was applied t o 19 widely different petroleum fractions in the 400' t o 1050' F. boiling range, including both cracked and virgin streams, and narrow as well as wide boiling fractions. These results are plotted
in Figure 1 as experiniental t'otal heterocompounds us. maximum possible lieterocompounds. The resulting correlation is theoretically rea,sonable, showing the experimental values lying about 2% below t,he maximum values. Some petroleum compound types are known to contain two hetero atoms per moleculee.g., carboxylic acids, hydroxyquinolines, et,c.-but the correla,tion of Figure 1 suggests that these amount t o a minor part of the total heterocompounds, a t least for samples boiling above 600' F. (the lower het'erocompound contents of Figure 1 refer primarily to samples with midboiling points below 550" I?.). This observation agrees with other unpublished studies carried out in this laboratory. Oxygen and nitrogen recovery figures were obtained for several of the samples of Figure 1, and these showed an average of 80% of t'otal nitrogen and 90% of total oxygen recovered in the heteroconipound chromatographic fraction. As previously discussed ( 3 , 4),
O/*W
NITROGEN
Figure 3. Estimation of heterocompounds by nomograph
contamination of the heterocompound fraction by hydrocarbons and sulfur compounds is negligible for samples boiling below 850" F., and minor for samples boiling below 1000" F. On the basis of these various checks of the accuracy of the method, the experimental determination of total heterocompounds is be1--2% weight. lieved accurate within For a fuller discussion of method accuracy and scope, see reference ( 3 ) . It was also observed for the samples of Figure 1 that there is an approximate relationship between sample oxygen and nitrogen contents. This fact permits the direct estimation of total heterocompounds when the sample boiling range and nitrogen content are known, as is frequently the case in our Laboratory for samples which are submitted for detailed compositional analysis. The molecular weight of the heterocompounds is first estimated as in Figure 2, and the per cent heterocompounds then obtained
*
from Figure 3. Comparison of experimental and estimated heterocompound values for the samples of Figure 1 shows a standard deviation of =t170 weight. Further comparison of experimental and estimated heterocompound contents with maximum heterocompound d u e s suggests that the accuracy of either estimated or measured heterocompound values is about the same, as long as total heterocompounds do not exceed 20%. Analysis of several shale oil samples (containing 30-45y0 heterocompounds) indicated that estimation is not reliable for such samples. Full size drawings of Figures 2 and 3 are available on request. EXPERIMENTAL
Determination of Total Heterocompounds. A 400-mm. X 12-mm. glass-Teflon column is packed with 4% H20-Al2O3 [see (d)], and 1 gram of sample (any petroleum related distillate) is charged. Elution is begun with 25%
volume benzene-pentane; 50 ml. are collected and discarded. A second 50ml. fraction is collected, eluting with 50yo volume methanol-benzene. The latter fraction is stripped of solvent under nitrogen on a steam bath and weighed. The weight of recovered fraction is assumed equal to the weight of heterocompounds in the original sample charged to the separation. Precision is =k0.37, weight. LITERATURE CITED
(1) Hastings, S. H., Johnson, B. H., Lumpkin, H. E., ANAL. CHEM. 28 1243 (1956). (2) HoM-ard, H. E., Ferguson, W. E., Snyder, L. R., $m. Sac. Testing M a leriabs, E-14 Meeting, St. Louis, 1965. ( 3 k Snyder, L. R., ANAL. CHEW 37, (13 (1965). (4) Snyder, L. R., Zbid., 36, 774 (1964).
Union Research Center Union Oil Co. of California Brea, Calif.
L. R. SNYDER
An Improved Mass Spectrometer Photoionization Source SIR: The use of a windowless photoionization source to produce ions for analysis in the 4EI 1Yf.S.9. Mass Spectrometer has been the subject of a recent studv ( 1 ) . DesDite its usefulness this source "is considered to be limited in its application. First the light beam enters the mass spectrometer through the vacuum lock port in the ion source housing. This prevents siniultaneous
use of a solid sample probe and thus places a serious limitation on the types of compound which may be studied. I n addition the possibility that a contribution from Dhotoelectrons was Dresent in the total ionization could n i t be discounted. Apart from electrons produced in the microwave discharge, it seemed possible that the quartz capillary used for transmitting the light from the
discharge to the ion chamber might be acting as a capillary multiplier of unknown gain. EXPERIMENTAL
The photoionization shown in ~i~~~~ has been designed and constructed with & view to eliminating the problems outlined abo.cre. I n general operating principle and basic construc-
I
I
2450 M/cs
Pumps gas inlet
Figure 1 .
Photoionization source VOL. 38, NO. 13, DECEMBER 1966
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