that solutions of OPT in aqueous HC1 or in ethanol give colored products with papverine. Similarly, Curzon and Giltrow ( 3 ) lia77e reported that aromatic 1,2-disldehydes yield colored or fluorescent uroducts with niany amino acids while aromatic I ,4-dialdehydes are inactiva. Xore recently, Amos and Gillis (1) have isolated rhe product of the reaction of OPT with o-phenylenedianiiiie and characterized it as a polycyclic compound: The reaction described by Curzon and Giltrow (3) occurs with a number of amino acids such a b glycine and histidine as well as with tryptophan. These authors have suggested the possibility of a Strecker degradation (6) as a possible mechanism. However, under the reaction conditions described above, a
number of amino acids including glycine, phenylalanine, histidine, ?-aminobutyric acid and 3,4-dihydroxypheny!alanine fail to yield any significant fluorescence. The mechanism of our reaction and the possible structure of the fluorescent product(s) are undergoing lurtlier study at the present time. The utility of OPT as a reagent for substituted indoles must be considered because the sensitivity of the reaction is such that as little as 5 x 10-9 gram of 5-methyoxylryptamine gives a fluorescent reading approximately four times that of reagent blank. LITERATURE CITED
( 2 ) Amos, D., Gillis, R. G., Australian J . Chem. 17, 1440 (1964).
(2) Bogdanski, D. R.,Pletscher, A., Brodie, B. B., Udenfriend, S., J . Pharmacol. Exptl. Therap. 117, 82
(1956). (3) Curzon, G., Giltrow, J., Xature 173, 314 (1954). (4) Snyder, S.H., Axelrod, J., Zweig, AI., Bzochem. Pharmacol. 14, 831 (1965). ( 5 ) Strecker, A., Ann. 123, 363 (1962). (6) Vanable, J. W., Anal. Biochem. 6 , 393 (1963). ( 7 ) Wachsmuth, H., Denissen, It., Van Koeckhoven, L., J . Pharm. Belg. 14, 386 (1959). R. P. MAICKEL F. P. MILLER Departments of Pharmacology and Psychology Indiana University Bloomington, Ind. 47401 WORK supported by USPHS grant AlH 06997. Presented in part at the ACS Southeastern Regional hIeeting, LOU~Sville, Ky., October 1966.
tatisn of Inverse Gas-Liquid Chromatography to SIR: Inverse gas-liquid chromatography (GLC) was recently described (2) a b a new technique for characterizing asphalts. Inverse GLC characterizes a nonvolatile stationary phase (asphalt, in this case) by observation of the retention behavior of known volatile test conipounds as they interact with the stationary phase. Most applications of asphalt make use of Its unique combination of physical and chemical properties. Oxidation of an asphalt in use often leads to premature failure of the product. Studies of the oxidation characteristics of asphalbs are therefore highly desirable. In the present correspondence, an extension of the technique is described by which the oxidation characteristics of an asphalt can be studied by oxidation of the asphalt in the GLC instrunaent, followed by examination with inverse GLC. Oxidation of an asphalt within the GLC column offers a number of advantages over conventional methods. EXPERIMENTAL
Apparatus. GLC data were obtained on a Beckman GC-2 gas chromatograph. Compressed air was substituted for the carrier gas during oxidation, and the instrument was modified to allow bypassing the column detector during the oxidation step. Procedure. A lir-inch by 13-foot C L C column was packed with one part of asphalt on 10 parts by weight of Fluoropak 80 (56 grams total). The column was then conditioned for a minimum of 6 hours using a helium inlet gage pressure of 15 p.s.i. and a n instrument operating teinperature of 130' C. (normal testing 1938
e
ANALYTICAL CHEMISTRY
conditions). Following conditioning, the test compounds were introduced individually and retention times determined as previously described ( 2 ) . The asphalt was then oxidized at 130' C. within the column by replacing the helium carrier gas with filtered air a t a flow rate of approximately 30 ml./ minute (15-p.s.i. inlet gage pressure). This rate was chosen to minimize nonuniformity of oxygen exposure along the column (I).. Except for rate studies, an oxidation period of 24 hours was used. Following oxidation, normal testing conditions were re-established and the oxidized column was again conditioned prior to obtaining test compound retention data. The interaction coefficient (I,) is a term devised for expressing inverse GLC data ( 2 ) . It is obtained by first determining the corrected retention volunies (Tin") on the asphalt column for a series of n-paraffins covering the molecular weight range of the test compounds used. The logarithms of the n-paraffin V R O ' S are plotted as a function of the molecular weight. The I , for a given test compound on the asphalt, column is then defined as 100 times the difference between the logarithm of the V R O of the test compound and the logarithm of the V R o of a hypothetical n-paraffin (obtained from the above plot) of the same molecular weight as the test compound ( 2 ) . The interaction coefficient i s thus a measure of the interaction of chemical functicnality in the test compound with chemical functionality in the asphalt. RESULTS AND DISCUSSION
Advantages of Oxidation within the GLC Column. The study of the oxidation characteristics of asphalts by direct oxidation within the GLC
column fol!owed by inverse GLC analysis offers a number of advantages ( 1 , 2 ) . Thin films of asphalt having reproducible thicknesses are easily prepared for testing on an inert column packing using conventional coating techniques. Easy and precise control over the temperature and air flow rate are possible during the oxidation period, making possible highly reproducible oxidation conditions. Oxidation of the asphalt within the GLC instrument eliminates the separate handling necessary when oxidation is carried out external to the GLC column; inverse GLC data can therefore be obtained on the asphalt before and after oxidation without disturbing the system. The oxidation-inverse GLC technique thus provides a means of obtaining highly reproducible data. Oxidation of asphalt while on the GLC column packing has the further advantage of providing a large ratio of surface area to volume. This is desirable both for reducing the time required tQreach a desired level of oxidation and to provide more uniform oxidation through the bulk of the asphalt, 'rhese advantages are particularly apparent when the method is compared to the batch-blowing technique in which it is extremely difficult to disperse the air uniformly in the viscous asphalt mixture. Viscosity considerations alone niay rule out the use of the batch-blowing technique for investigation of many asphalts in the lower temperature ranges. Behavior of the Interaction Coefficient on Oxidation and Correlation with Durability. The ability of inverse GLC to indicate chemical changes in a n asphalt on oxidation
200
I
I
I
1
i
I80
I
60
I40
_-30
40 50 60 70 80 90 ACCELERATED WEATHERIMG D U R A B I L I T Y , d a y s t o f a i l u r e
100
Figure 2. Relationship between interaction coefficients and durability of nine asphalts
20
0
Asphalt durability data and numerals associated with data points are taken from references (3, 4)
1 6
12
I8 24 30 36 OXiDATiON TIME, haur6(l3OoC 1
42
48
Figure 1. Change in the interaction coefficient on oxidation of an asphalt 0 1 -Methylpyrrolidine Formamide I Phenol A Pyrrole @ Propionic acid 0 Butanol
grade asphalts. Durability data are also shown in Table I. It can be noted that a good correlation exists between the phenol I , values and the accelerated weathering durability of the asphalts. These data are plotted in Figure 2. Correlative trends are also evident for the test compounds triethylamine and propionic acid. The asphalts, which were chosen to cover a wide range of durabilities, were previously studied by Greenfeld and Wrieht (3. L) who obtained the durability data. These data were obtained in a carbon-arc accelerated weathering device, and are a measure of the susceptibility of the asphalts to oxidative degradation in the presence of ultraviolet light. u
and also differentiate among asphalts on the basis of these changes has been demonstrated ( I ) . The behavior of the interaction coefficient, I,, on oxidation of an asphalt [asphalt No. 4 ( 2 ) ] is shown in Figure 1. In the figure the I,'s of six different test compounds are shown for oxidation periods in the GLC column of 6, 12.24, and 48 hours a t 130' C. Characteristic features of this plot include the different behavior patterns of the test compounds, the high initial rate of increase in I,. and the leveling off of the rate oi increase in I , after the first 12 hours of oxidation (except 24 hours for 1-niethylpyrrclidine) . Examination of the high initial rate of increase in I , on oxidation in Figure 1 indicates that I , would be most sensitive t o any oxidation that might occur in the asphalt before testing; thus prior oxidation would reduce the magnitude of the change in I p obtained during the rolunin oxidation procedure. After 24 hours of oxidation, the I , for all test compounds has leveled off a t a near-maximum value with little change on further oxidation. The value of I , after 24 hours oxida-
tion appears to be unique for each asphalt and may haye practical significance. For example, the data in Table I show the I , values, obtained after 24 hours oxidation, for four selected test compounds with a group of nine coating-
Table 1.
Inverse GLC and Durability Data on Greenfeld and Wright Asphalts
Test comDound -1, after oxidations Propionic Durability, Asphalt n0.c Triethylamine acid Phenol Formamide daysb GW-2 100 81 141 146 69 GW-3 135 105 153 162 53 GW-5 43 73 122 151 95 32 GW-9 i13 168 >l50 177 GW-19 126 38 71 141 95 GW-22 114 91 151 60 15; GW-89 51 76 142 147 65 GW-239 130 93 154 105 77 GW-248 53 >150 76 156 150 a 24 hours, 130" C., 15-p.s.i. air inlet pressure. b Data from Greenfeld and Wright (3, 4). Csing a carbon-arc accelerated weathering machine in accordance with daily cycle A in Recommended Practice for AcceleratedWeathering Test of Bituminous >laterials (D529-59T), 1961 Book of ASThI Standards, Part 4, p. 1233. Sample designations are Greenfeld and Wright numbers prefixed with GW.
VOL. 38, NO. 13, DECEMBER 1966
1939
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
0Virgin sampler V
1940
Blends of cracked and virgin streams
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
