ANALYTICAL CHEMISTRY
1632 reaction rates are desirable is well known. I n recent years these advantages have been recognized and used for catalase studies (4161.
Another factor in determining catalase activity is concerned with the concentration of hydrogen peroxide t,o be used. Early in our work oncatalase it wasobserved that different enzyme preparations react differently toward the concentration of hydrogen peroxide. Figure 9 shows a study of the effect of hydrogen peroxide on the activity of green and etiolated barley seedlings of the same age. It is evident that in order to obtain the maximum activity it is necessary t o use a much higher concentration of hydrogen peroxide for the etiolated than for the green plants. In preparations of avocado fruit tissue the maximum activity is reached a t a hydrogen peroxide concentration of 10 to 12 A’. On the other hand, animal tissues, such as rat liver, kidney, or erythrocytes, require an approxinately 1 N concentration of hydrogen peroxide to give a maximum rate. As they have no determinations on isolated or purified catalase from these sources, the authors cannot say whether these different responses to hydrogen peroxide concentration are due to a difference in the catalase or in the accompanying substances. However, a commercial preparation of beef liver catalase gave a masimuni activity a t approximately 1 N . A preliminary determination of the rat,e of oxygen evolution aa a function of hydrogen peroxide should be made on each new
material to be studied. Then a concentration of hydrogen peroxide close to that which gives the maximum rate should be chosen, such that the activity factor remains constant when the amount of catalase preparation used is half and double the amount used for the maximum rate determination-i,e., the reaction should remain f i s t order with respect to catalase. The apparatus described may be used for studying other reactions that involve the measurement of the rate of evolution or absorption of a gas a t constant pressure. The apparatus is very flexible and can be readily adapted for either very fast or very slow rates by changing the size of the manometer, the speed of the synchronous motor, or the size of the pulley over which the ribbon passes. The size and shape of reaction vessel may also tie changed to suit any particular study. LITERATURE CITED
Balls, A. K., and Hale, W. S., J. Assoc. Ofic.A n . Chemists, 15, 483-90 (1932). Chance, B., Rev. Sci. Instruments, 18, 601 (1947). Green, A. A., J . Am. Chem. Soc., 55, 2331-6 (1933). Greenstein, J. P., Jeurette, W. V., and White, Julius, J . Natl. Cancer Inst., 2,283-91 (1941). Shardakov, V. S., Compt. Tend. acad. sci. U.S.S.R., 24, 66-13 (1939). Slier, I. W., J . Biol. Chem., 154, 461-73 (1944). RECEIVED Marcli 5 , 1951
Determination of Nitrogen in Shale Oil and Petroleum APPLICATION OF ESTABLISHED METHODS JOHN S. BALL
AND
ROBIN VAN METER, U. S . Bureau of Mines, Laramie, Wyo.
An adequate method for the determination of nitrogen is highly important in the investigation of shale oils because of the large quantities of nitrogen present and the effect of nitrogen compounds on the properties of the oils. The nitrogen contents of three samples, a shale oil and two fractions therefrom, as determined by seventeen different laboratories using their own methods, showed that there
N
ITROGEN waq recognized as a constituent of oil shales as early as 1845, when Selligue (1)developed the recovery of by-product ammonium sulfate in connection with the French shale oil industry. In 1854, Williams (2) reported the isolation and identification of pyrrole, pyridine, and substituted pyridines from the oil retorted from Dorsetshire English shale. Robinson (2)reported the isolation of quinoline bases from shale oil in 1879. Difficulty has been experienced (3) in nitrogen determinations on petroleum, and special methods were developed. The refractory nature of pyridines and quinolines is well known. The nitrogen content of shale oil materials may range from as high as 10% for low boiling tar bases, down to 0% for highly refined fuel and by-product fractions. Some difficulty had previously been experienced in analyzing such materials a t the U. S. Bureau of Mines a t Laramie, Wyo., and others working with shale oils reported similar difficulties with nitrogen analyses. EXCHANGE PROGRAM
I n order to investigate whether the determination of shale oil nitrogen presents a real problem, an exchange program &asundertaken involving seventeen laboratories. Many of the laboratories were those of major oil companies interested in shale oil
was no consistency of results among laboratories. Methods used included both Dumas and Kjeldahl, and micro, semimicro, and macroprocedures. The need for an accurate, reproducible method for the determination of nitrogen in shale oil was demonstrated. No clear superiority for any method or procedure was shown, but the macro-Kjeldahl procedure appeared the most promising.
work, but several laboratories working on coal tar chemicals were represented. Samples of a crude shale oil, a naphtha-boiling range fraction from shale oil, and a Diesel fuel-boiling range fraction from shale oil were submitted to each laboratory. Each laboratory was asked to make nitrogen determinations by those procedures currently used in that laboratory. Results of analyses made by Kjeldahl and Dumas methods on macro, semimicro, and micro scales were reported. Figure 1 shows average values obtained by each of the laboratories for each of the six variations used. Table I presents these data in a different manner to give the minimum, maximum, and average values. The number of laboratories contributing data in each instance also is shown. The nitrogen values in Table I and Figure 1 show that the Kjeldahl methods tend to yield lower values than the Dumas methods. Certain types of errors, such as those made in obtaining sample weight, reading of volumes, etc., may be common to both general methods and are as likely to be positive in sign as they are to be negative. More than 60 individual Kjeldahl determinations and 30 individual Dumas determinations are represented, and so errors of this type may be considered to compensate. However, there are possibilities of errors inherent in the Kjeldah1 methods that could not occur in Dumas methods, and vice
V O L U M E 23, NO. 1 1 , N O V E M B E R 1 9 5 1
1633
CRUDE SHALE OIL LSOA-48-119)
9
micro a i d semi-mi'cro I
2 a
Q -1
.I
f
4
.
micra and semi-micro
1
-
.
1
a "
macro e
a
&
b
.
a.
versa. The most protxtble eirois ot this t \ y e in the Kjeldahl method are incomplete conversion of the organic nitrogen to aninlonia, loss of ammonia from the digestion step, or incomplete absorption of the ammonia. ,411 of these would tend to make the Kjeldahl value low. In the Dumas method, the errors of this type are incompleteness in the burning of sample, in sweeping nitrogen from the combustion tube, in reduction of nitrogen, and in absorption of carbon dioxide. Normal attention to procedure detail precludes the first two occurrences that ~vouldlead to obtaining low results. However, if nitric oxide enters the nitrometer, or if cracking preceding combustion causes methane or other hydrocarbon gases or carbon monoxide to enter the nitrometer, or if absorption of the carbon dioxide is incomplete, the results will be high.
Table I.
These considerations would suggest that the higher values of a group of Kjeldahl determinations and the lower values of a group of Dumas determinations should be closer to the true value. Examination of Figure 1 shows a distribution of results as expected. A concentration of close-checking results for the macro-Kjeldahl 'procedure is apparent for each sample, and most of the other values are somewhat lower. The microDumas resuks on the crude oil similarly shon a concentration of results, but the scatt,ered values are mostly on the high side. The coincidence of the two concentrations in the case of the crude oil is remarkable and is taken as indicating the best, value of the nitrogen content. For the other two sanlples, no such support was found between the two methods. However, the Dumas results agreed as well with the concentration of Kjeldahl results as with any other value. A selection of a best value was made on the basis of the largest group of Kjeldahl results. These values are: for the crude oil, 1.94% nitrogen; for the naphtha, 0.9570; and for the Diesel fraction, 1.61%. In Table I1 are shown the percentages of submitted results that are within acceptable limits, defined arbitrarily as within 2YOof the best value. Doubling the magnitudr of the limits includes very few additional values; therefore, the acceptable limits adopted do not appear to be unreasonably restrictive. .a
Table 11.
Method and Scale of Analysis Iijeldahl, macro , Dumas, micro Dumas, semimicro Dumas, niacro Kjeldahl, mlcro Kieldahl semimicro
Nitrogen Values Reported for Exchange Samples Nitrogen, %
Method and Scale of Analysis Kjeldahl Macro Nin. Max. Av. S o . of labs reporting Semimicro Min. Ma&
Shale o i l Diesel fuel fraction ~~~~~~
2.10 1.82 14
1.31 1.67 1.54 14
2.18 2.18 2.18 1
1.41 1.41 1.41 1
1.79 1.79 1 79 1
2.15
1.43
0.55 1.14 0.90 7
1.00 1.75 1.43 7
reporting
1.80 1.82 1.81
2
0.85 0.92 0.89 2
1.59 1.79 1.69 2
1.20 1.20 1.20
reporting
2.34 2.34 2.34 1
1
1.60 1.97 1.79 2
1.74 2.41 2.03
0.94 2.17 1.36 9
1.45 2.04 1.77 9
AV.
AV.
.
Shale oil naphtha 0.64 1.02 0.89 13
S o . of labs reporting Micro hlin. Max.
KO.of labs Dumas Macro Min. hlax. Ar h-0. of labs Semimicro Nin. Max. Av h-0. of labs Mcro Nin. Max. Av. h-0, of labs
Crude shale oilI
reporting
reporting
1.15
1.79 7
10
Percentage of Submitted Results Acceptable Limits
~~
~-
Results Submitted 41 28 4 6 23 3
Results Acceptable 17 9 1 1 1 0
~~
within
Percenta e Acceptabf;e 41 32 25 17 4 0
~-
ANALYTICAL PROCEDURES USED
On the analytical report forms supplied to cooperating laboratories, a literature reference to the procedures used was requested, as was a statement as to nhether or not the procedure had been altered significantly. The range of responses makes correlations of procedures with results a difficult task; however, examination of the information supplied showed that no analytical procedures exhibited ndl-defined superiority. The results obtained from application of a given analytical method appear to have been influenced both by the procedure used for analysis and by the technique of the analyst carrying out the procedure. Thus, in more than one instance, a laboratory carrying out analyses by it Kjeldahl macromethod procedure obtained results within acceptable limits of accuracy, whereas another laboratory indicated to be using the same procedure failed to obtain results within acceptable limits. On the other hand, two quite different Kjeldah1 macromethod procedures yielded results within acceptable limits. -4 complete knowledge of all of the procedures usetl, in-
1634
ANALYTICAL CHEMISTRY
cludiiig details of modification, if any, would be necessary before valid comparisons of the merits of the procedures could be made. There is evidence that procedures are not commonly written to include all significant detail, as different results can be obtained when using the same method.
dicates the difficulty of the problem. This probably arises from the occurrence of nitrogen in ring compounds, which are more refractory than the compounds commonly analyzed by current procedures for nitrogen determination. ACKNOWLEDGMENT
COMPARISON OF METHODS
Although there has been some dispute as to whethei both Kjeldahl and Dumas methods were suitable for the deter niination of nitrogen in shale oil, the results, aa shoun in Table 11, indicate that either method can be made t o give satisfactory results. The Kjeldahl method on a macro scale gave the greatat percentage of satisfactory results. It also was used to the greatest a t e n t , and experience probably contributes to the amount of sttisfactmy data. The Dumas method, as practiced on a micio ale, waq used less and gave slightly fewer satiifactory data. Insufficient data were submitted to draw any conclusions regardiag Dumas analyses on macro and semimicro scales and Kjeldahl i'alvses on a semimicro scale. The lack of satisfactory results by the Iijeldahl method on a micro scale suggests that difficulties, probably of technique, arise when the scale of the method is reduced. Some difference may be noted in the efficacy of the method8 on the different samplra (see Figure 1 ) . The Kjeldahl maciomethod was consistent 011 all samples. The Dumas micromethod was much better with respect to the crude oil than with the other two samples. The low percentage of satisfactory results by all methods 111-
The following laboratories participated in the exchange program: The Barrett Division, Allied Chemical & Dye Corp.; California Research Corp.; Jackson Laboratory, E. I. du Pont de Nemours & Co., Inc.; Louisiana Division, Esso Standard Oil Co.; Gulf Research & Development Co. ; Huffman Microanalytical Laboiatories; Koppers Co., Inc.; Phillips Petroleum Co.; Shell Development Co.; Socony-Vacuum Laboratories; Process Division, Standard Oil Development Co.; Research Division, Standard Oil Development Co.; The Texas Co.; Union Oil Co. of California; Universal Oil Products Co. ; Oil-Shale Demonstration Plttnt, U. s. Bureau of Mines; and Petroleum and OilShale Experiment Station, U.S.Bureau of Mines. LITERATURE CITED
(1) Racon,
R. F.,and IIamor, W. .I.,"The American Petroleum
Industry," y. 808. Kea- Tork, AIcGraw-Hill Hook Co., Inc., 1916. (2) NcRee,
Ralph H., and co-authors, "Shale Oil." pp. 1 7 6 6 , S e w Tork, Chemical Catalog Co., 1925. (3) Poth, E. J., Armstrong, W. D., Cogburn, C . C'., :tiid Bailey, J. R., I d . Eng. Cheni., 20, 83-5 (1928). RI:CLI\.ED JIarcli 3. lCI31,
(Determination of 2Yitrogen in Shale Oil and Petroleum)
EFFECTS OF DIGESTION TEMPERATURE ON KJELDAHL ANALYSES G. H . L i K E 4 h D PHILIP MCCLTCII4Y, b-nion Oil Co. of Culifornia, Wilmington, calif., HOBI\ \ AY METER AND J. C. YEEL', C . S. Burenit of Wines, Larumie, Wyo. A survey had shown both that present methods for nitrogen determination were unsatisfactor) and that the Kjeldahl method used on a macro scale had promise. Investigation of the variables in the Kjeldahl procedure revealed that the temperature attained in digestion of the sample .was of prime importance. Too low a temperature either requires too long a digestion time or fails to give good results, while too high a temperature may result in loss of
M
ANY attempts have been made to improve t h e Kjeldalil method for nitrogen determination since 1883, when the procedure Mzas first published. Goals sought have included greater accuracy and precision, applicability to more refractor), types of compounds, reduction of digestion time, simplification of the procedure, and others. Bradstreet (2) and, more recently, Kirk ( 4 ) have extensively reviewed the principal published work on the Kjeldahl method. Two significant advances in the method had been made before the turn of the century. Kilfarth (9) has been credited with introducing the use of mercury in the digestion and Gunning ( 3 ) with introducing potassium sulfate. Both of these additions resulted in material improvement in the method by permitting shorter digestion times and by broadening the scope. Much of the later work is contradictory to a point where the confusion now existing in the practice of the Kjeldahl method is quite understandable. Many modifications have been proposed and 1
Piebent address, S.
W.Shattuck Chemical Co.. Denver. Cola.
9ND
nitrogen. Adjustment of the amount of potassium sulfate in the digestion mixture to give the proper temperatures resulted in a procedure which has giien satisfactorj results on a large number of samples. The concept of a narrow temperature range w-ithin which satisfactor) results may be obtained by the Kjeldahl procedure permits modification of the standard procedure on a logical basis to meet requirements of special samples or conditions.
have met with opposition. These include digestion mixtures using selenium oxychloride, selenized pellets, copper sulfate, perchloric acid, and hydrogen peroxide (30:; ), either singly with a form of mercury or in combinations. By a c.ritical study of the operating conditions, a procedure baaed on the Gunning and JVilfarth contributions has been developed which has proved to be satisfactory for analyzing petroleums and shale oils for nitrogen content. Such oils mag contain nitrogen in pyridine ring structures, and in this form the nitrogen is particularly refractory to Kjeldahl digestion. Digestion a t temperatures below 370' C. will not give quantitative recovery of pyridine wit,h 1-hour digestion; a t temperatures abdve 410" C. nitrogen may be lost by decomposition. Since the beginning of this research a somewhat similar concept has been proposed by Ogg and Willitts ( 5 ) rvorking in another field. .4lso, White and Long ( 8 ) , working with sealed digestion tubes on a micro scale, have sucmssfully employed a digestion temperature of -170" C. with still shorter digestion times. Because close attention to procedure is necessary to attain the satisfactory diges-
