the procedures, aliquots of standard iron, lead, and arsenic solutions were added to one of the samples previously analyzed and the synthetic mixtures carried through the procedures. Recoveries were good (Table 11). ACKNOWLEDGMENT
The authors thank Samuel Sitelman for his suggestions, and Leonard Markowitz for his preliminary experimental
work on the colorimetric method for iron. LITERATURE CITED
(1) Am. SOC. Testing Materials, Philadelphia, Pa., “1956 Book of ASTM Methods for Chemical Analysis of Metals,” p. 486. (2) Bartlet, J. C., Wood, X., Chapman, R. A., ANAL. CHEM.24, 1821 (1952). (3) \ , Cushman. A. S.. J . I n d . Eno. C h a . 10, 376 (19i8). ’ (4)McNabb, W. hl., Wagner, E. C.,
ESG.CHEM., A N A L . ED. 2, 261 (1930). (5) Mjlitary Specification NILA-l59B, Antimony Sulfide. (6) Rodden, C. J., J. Research Natl. Bur. Standards 24, 7 (19:O). (7) Sandell, E. B., Colorimetric Determination of Traces of Metals,” pp. 141, 282, 555, Interscience, Sew York, 1959, (8) Scott, W.W., “Standard Methods ot Chemical Analysis,” Vol. 1, p. 505, Van Nostrand, New York, 1939. RECEIVEDfor review February 2, 1960. Accepted May 23, 1960. IND.
Sensitive Spot Test for Nitrogen Compounds in Petroleum Fractions PAUL V. PEURIFOY and MAXWELL NAGER Houston Research Laboratory, Shell Oil Co., P. 0.Box 2527, Houston I , Tex.
The nitrogen content of petroleum fractions may b e rapidly estimated by visual comparison of colored spots produced by the reaction of nitrogencontaining compounds and tetracyanoethylene on filter paper.
Two pounds air pressure. Filter paper, Whatman No. 120, drop reaction paper. Weisz ring oven, National Appliance Co., H. Reeve Angel &- Co., Inc., agent. EXPERIMENTAL PROCEDURES
T
USE of tetracyanoethylene (TCNE) as a spot test reagent for aromatic hydrocarbons on filter paper has been described (3, 4). This reagent can also be used for the detection of other substances. Hydrocarbon-TCNE colors which persist a t room temperature are unstable upon heating. I n contrast, however, many organic compounds containing hetero atoms, especially nitrogen compounds, leave a color on the paper after heating. Two semiquantitative techniques for the determination of total nitrogen in petroleum fractions have been developed. One method employs simple spraying and the other involves the Weisz ring oven (5). HE
REAGENTS A N D APPARATUS
TCNE was prepared in this laboratory by the dibromomalononitrilepotassium bromide complex method (1) or obtained from Eastman Organic Chemicals on special order. The compound is best purified by sublimation, but may be recrystallized from chlorobenzene (10 to 1). Because TCNE s l o d y evolves hydrogen cyanide on exposure to moist air, the reagent should be stored in a dark bottle under a blanket of inert gas. Pipets, 0.1 ml., Kahn-type. Spray bottle, 50-ml. glass reagent spray, Type R (Microchemical Specialties Co.. Berkeley, Calif.).
Detection of Nitrogen Compounds in Presence of Aromatic Hydrocarbons. Apply 0.05 ml. of sample to a square of filter paper ( = 23/4 inches square) supported on a 100-ml. beaker. When the sample has completely soaked into the paper, place in a vertical position and spray with a saturated solution of T C S E in benzene for 2 seconds from about 31/2inches. Place test paper in an oven a t 110’ C. for 5 minutes. Observe color and compare with colors of knolms. Ring Oven-Acetic Acid Method for Detection of Nitrogen Compounds in Presence of Aromatic Hydrocarbons. Place three pencil dots 11 mm. apart in line on a square of filter paper. Apply 0.05 ml. of sample to paper at the center dot. Center the sample paper on ring oven and with a capillary pipet, wash the sample spot with 60% acetic a d until the acid-wet area reaches the outer pencil dots. Place the test paper in an oven a t 110’ C. for 5 minutes. Remove the paper from the oven and allow to cool to room temperature. Spray as above with TCNE solution for 4 seconds. Heat the paper a t 110” C. for 5 minutes and compare colors. Color comparisons can be made with
a series of samples of known nitrogen content treated by the same procedure or with a series prepared by dilution of a single known with nitrogen-free solvents-e.g., benzene, paraffin oil, iso-
octane-of about the same viscosity as the sample. Solvents used for dilution should have about the same viscosity, so that the spots will have the same area. An unknown sample may be diluted to obtain comparison with a known. Petroleum oils from different sources with the same nitrogen content may have slightly different colors, but a t low concentrations most samples appear to have about the same color. This is true below 100 p.p.m. for the simple spray method and below 10 p.p.m. for the ring oven method. I t is preferable to make estimates using knowns similar in composition to the unknowns; however, if knowns of different types must be used, comparisons are best made by dilution to the ranges specified above. Spots produced using the ring oven method have a narrow outer ring and a lighter inner spot. Comparisons should be made using the inner spot. RESULTS AND DISCUSSION
The nitrogen compounds tested include pyrroles, pyridines, indoles, pyrazoles, imidazoles, acridines, carbazoles, quinolines, and aliphatic and aromatic amines. The limit of detection appears to be in the range of lo-’ gram. Among the other hetero compounds tested, only the hydroxyl compounds and aromatic thiols seem to give colors sufficiently intense to interfere. Thiophenes leave no color; other sulfur compounds leave colors of very low intensity. Peroxides and hydroperoxides give only light or no colors. The colors produced by the VOL. 32, NO. 9, AUGUST 1960
1135
Table 1.
TCNE-Nonhydrocarbon Colors
Compound
Initial Color
Color after Heating
Aldehydes Benzaldehyde n-Heptaldehyde
Kone None
None None
Light yellow Red Blue None Blue Yellow
Light yellow Light yellow-green Light yellow None Light brown Yellow
Table II. Estimation of Nitrogen Content by TCNE Spot Test
Sample (Time Taken, Hours) 0830 0840 0845 0850
Hydroxyl eompounds Benzyl alcohol p-Cresol 2,6-Di-tert-butyl-p-cresol
Inositol 1-Xaphthol 2-0ct an01 Sitrogen compounds Amines %-Butylamine N,N-Diethyl-o-toluidine N.N-Dimethvl-D-ahenvlazoaniline Di-2-naphth&&ne Diphenylamine n-Octadecylamine Piperidine Heterocyclics Acridine Benzimidazole Carbazole 3,5-Dimethylpyrazole 8-Quinolinol Indole 2,4-Lutidine Porphyrin Pyridine Benxothiazole Pyrrole 1,2,3,4-Tetrahydrocarbazole Quinoline
None Green Green Violet Aqua None None
Brown Red-brown Yellow Light yellow Lavender Brown Light yellow
Green Yellow Blue Gold Blue Blue Yellow-green Light green Yellow Gold Gold Purple Yellow-green
Yellow-green Yellow Light yellow Gold Gold Orange Green Tan Yellow Tan Gold Light brown Yellow-green
None Kone Yellow
Very light yellow Very light yellow None
Rust Red Red Purvle Green
Very light yellow None Very light yellow Very light yellow Very light yellow
Purple Pink Gold
Sone None e None
Blue Rose Purple
Very light green Very light yellow Very light yellow
Sone Yellow Sone None
None None Light brown Light brown
Peroxides Benzoyl peroxide tert-Butyl peroxide Cumene hydroperoxide Sulfur compounds Disulfides Benzyl disulfide tert-Butyl disulfide Phenyl disulfide p-Tolyl disulfide Thianthrene Heterocyclics Dibenzothiophene 2-tert-Butylthiophene Thiophene Sulfides p-Cresyl ethyl sulfide %-Hexyl sulfide Phenyl sulfide Thiols T'henylmethanethiol 1-Tetradecanethiol 2-Naphthalenethiol p-Toluenethiol
1 136
ANALYTICAL CHEMISTRY
0855 0905 0915 0920 0925 0940 1000
1010 1030 1130 1140 1145 1150 1155 1200 1215 1230 1300 1330 Hydrogenated white oil product
Xitrogen ContentTCNE IbIodified method Kjeldahl TOO
75
6i4
...
69
...
33
50 25 15
10 15 15
23
i5
150 200 300 500 550 600 600 0"
13
a -4ssumed to be free of nitrogen compounds; although some color was observed, it was less than that of lowest sample.
compounds studied are given in Table
I. It was possible to detect concentrations as low as 0.5 p.p.m. of nitrogen as solutions of indole and quinoline in paraffin oil. In using carbazole the detection limit was in the range of 1 to 5 p.p.m. even though carbazole gives one of the lowest color intensities of the nitrogen compounds tested. Sensitivity can be increased at' low concentrations by using the Weisz ring oven technique, which lowers the detection limit 5- to 10-fold. Color comparisons made rvith known concentrations of pure compounds indicat'e that the average deviat'ion from t'he t'rue value is =t20 p.p.m, in the 100p p . m . range and & l o % in the 100to 1000-p.p.m. range. This was confirmed on practical samples dubricating oil distillate, hydrotreated catalytically cracked light gas oil, and finished transformer oil) for which nitrogen determinations are independently available. The color bodies present in relatively dark oils do not interfere with the test. Although the chemistry of the reaction of TCKE with nitrogen compounds (amines) has been studied in some detail, we are uncertain as to how much of the chemistry in solution applies to paper spot tests. Thus hlcKusick et al. ( 2 ) report that TCKE does not react with tertiary aliphatic amines. However, both triethylamine
and tri-n-butylamine give intense colors with TCNE on filter paper. This spot test can be useful as a quick quality control test for hydrotreating units wherein the extent of nitrogen removal is of significance. The T C K E spot test method for nitrogen has been applied to a series of nitrogen-containing (range: 10 to 700 p.p.m.) samples obtained from a hydrotreating pilot plant study of crossover from a high-nitrogen to a low-nitrogen feed. Xtrogen contents were estimated by comparison with samples of known nitrogen content from other sources. Results for this series of tests and nitrogen values obtained by a modified Kjeldahl method are given in Table 11. The 22 spot tests were completed in 3 hours, while the Kjeldahl method on only six samples required about 1 day. A comparison of T C N E values with Kjeldahl values for a number of other petroleum oils such as West Texas and California lubricating oils and catalytically cracked gas oils is shown in Table 111. Thus, the T C N E spot test offers a means of locating aromatic hydrocarbons separated on paper and a rapid semiquantitative determination of total nitrogen in hydrocarbon samples.
Comparison of Nitrogen Content by TCNE Spot Test and Kjeldahl Methods
Table 111.
Sample
1
2
California high viscosity lube oil, 85-90 SSU/2lO 1 2 3 4 5 6 7 8 9 10 11
12
Kjeldahl
1080 1240
1080 1200 RIacro 344 357
350 350 550 550 300 300 260 200 125 75 100 150
Semimacro 330 363
...
...
580 594
310 291 265 205 139
... ...
...
...
116
96 140
Furnace oil 75 50 50
72 56 44
Light sour gas oil 1 2
30 30
26 24
Transformer oil, 60 SSU/lOO 1 2
40 40
38 35
1
2 3
ACKNOWLEDGMENT
The authors express their appreciation to Shell Oil Co. for permission to publish this work, to S. C. Slaymaker for the preparation of tetracyanoethylene, and to E. W. Roe for some of the analyses.
TCNE
West Texas high viscosity lube oil, 950 SSU/lOO
LITERATURE CITED
(1) Cairns, T. L., et al. J . A m . Chem. SOC. 80,2775 (1958). (2) McKusick, B. C., et al., Zbid., 80, 2806 (1958). (3)TPeurifoy, P. V., Slaymaker, S. C., hager, M., ANAL. CHEM. 31, 1740 (1959).
(4) Tarbell, D. S., Huang, T., J. Org. Chem. 24, 887 (1959). ( 5 ) Weisz, H., Chem. Age (London), 1955, 131Y
RECEIVED for review January 28, 1960. Accepted May 23, 1960. Division of Analytical Chemisfry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
Quantitative Determination of Traces of Vanadium, Iron, and Nickel in Oils by X-Ray Spectrography C. W. DWIGGINS, Jr., and H. N. DUNNING Bureau o f Mines, Petroleum Research Center,
b An accurate x-ray internal standard method has been developed for the determination of vanadium, iron, and nickel in oils. Only the addition of a b l e n d e d c o b a It-c h romi um internal standard is required, and the three metals may b e determined without removal of the sample from the x-ray spectrograph. An emission-absorption method has been developed for special cases in which an internal standard may not b e used. Several x-ray methods of trace metal determination are compared.
U. S. Department o f the
X
Inferior, Bartlesville, Okla.
methods have been used frequently for the determination of trace metals in oils (2, 3, 7 ) . Such methods permit the direct determination of the metals in petroleum much more rapidly than the usual ashing methods (5, 6, 9) and eliminate possible losses of volatile metal complexes ( 3 ) . Corrections must be made for the variation of the mass absorption coefficients of various samples to ensure accuracy. These corrections are necessary in petroleum analyses mainly because of the wide range in sulfur con-RAP
centration. If the sulfur content is known, the contribution of sulfur to absorption may be calculated (7’). However, petroleums are found occasionally that contain several per cent of brine, which greatly increases the mass absorption coefficients. In many such oils, the brine forms a stable, very viscous, emulsion with the oil which may be broken quantitatively orily with a n ultracentrifuge. Because such oils may appear normal on usual observation, it is desirable to have methods that give results independent of the brine content. VOL. 32, NO. 9, AUGUST 1960
1137
