for &he separation of hydrocarbon nlixtures. Samples froin 2 to 20 ml. were fractionated. The order of displacement was paraffins, inonocycloparaffins, and aromatics. Binary mixtures of paraffins and cycloparaffins were separated, and paraffin and cycloparaffin fractions of purity higher than 99% were recovered from naphtha. There was a definite tendency for the yeparation of mono- and dicyclopar:iffins, a fraction containing 76y0 dic,j.cloparaffins having been obtained frorn a California naphtha distillate. Thie technique should p r c n ~ useful
to coinpoiient analysis, and to the preparation of fractions for spectrometer calibration in hydrocarbon type analysis.
(5) Kurtz, S. S.,Jr., Mills, I. W., Martin, C. C., Harvey, W. T., Lipkin, M. R., ANAL.CHEM.19, 175 (1947 j. (6) Mair, B. J., Zbid.,28, 52 (1956). (7) Mair, B. J.. Glaseow. A. R.. Jr.. Rossini. F: D
LITERATURE CITED
Begeman, C. B., Cranier, P. L., firid. Eng. Chern. 47, 202 (1955). Brown, K. .4., ANAL. CHEX 23, 430 (1951). Doss, 31. I?., "Physical Coiistafits of the Principal Hydrocarbons, 3rd ed., The Texas Co., New York, 1942.
(4)Jones, A. I,., hlilberger, E. C., I n d . Eng. Chem. 45, 2689 (19531.
Sullivan, L. J., Rumel, T.C
I L u h n m kor review Oecember 18, 1956 Accepted April 19, 1957. Division of Petroleum Chemistry, 130th Meeting ACS, Atlantic City, N. J., Septembfv I950
Determination of Tetraethyllead in Gasoline JOHN J. RUSS and WENDELL REEDER Campbell Taggart Research Corp., Dallas 7, Tex
F A method for rapid and accurate determination of tetraethyllead in gasoline is presented. The separation of lead as lead sulfate followed by complexometric titration with standard disodium dihydrogen (ethylenedinitrilo) tetraacetate eliminates the interference due to iron or gasoline dye. A deviation of duplicates from their mean is 0.004 for the range 1.7 to 3 ml. of tetraethyllead per gallon.
T
accepttd mrtllods for the determination of tetravthyllead in gasoline are the -4STRZ lcad chromate method ( I ) , the ASThS polarographic method (a). and x-ray techniques (6, 11). The ASThI lead c4hromate method involves acid hydrolysis of the tetraethyllead with concentrated hydrochloric acid followed by gravimetric determination of lead as chromate. This method is accurate but both lengthy and tedious. The polarographic and x-ray techniques are suitable where proper instrumentation is available. The original investigations of Biederinann and Schwarzenbach (6) of the coniplex ionq of the alkaline-earth and other metals with disodium dihydrogen (ethylenedinitrilo) tetraacetate have been extended considerably by other workers (3, 4,7, S, 10, 19-14). Milner and Shipman (12) published a method for the determination of tetraethyllead in gasoline incorporating the technique devised by Flaschka (9). Lead is titrated a t p H 10 in ainmoniacal tartrate medium using Eriochrome Black T (F-241) as the indicator. The indisHE GENERALLY
tinct purple-to-blue end point obtained by Flaschka was improved considerably by adding a known amount of standard magnesium solution. This method was found to be generally applicable; however, in numerous instances serious interference with the end point was due to the presence of iron or to the dye used to identify the gasoline. Using the method of hlilner and Shipman ( I $ ) , iron a t a level of 0.24 p.p.m. in the final titrating solution gives some fading of color a t the end point. It is impossible to obtain an end point if iron exceeds 0.32 p.p.m. Analysis of filtered samples of three gasolines, by the well-known o-phenanthroline colorimetric method, shows the gasolines t o contain 0.8 to 0.9 p.p.m. of iron. A 50-ml. sample of gasoline containing 0.S p.p.m. of iron would produce interference in the Alilner and Shipnian method. Accordingly, the purpose of this investigation m s to provide an accurate, rapid method free of all possilde interferences. APPARATUS
Reflux n-.;embly, Allihn coiidenaer, 300 niin. in length, and flat-bottomed extraction flask, 500-ml. capacity with standard-taper neck 24/40 to fit condenser. Burner, Fisher, high temperature, 42mm. grid. Boiling stones, heavy porcelain c h i p , free of iron. Antispattering rod, glass, 6 inches long, 3 to 5 mm. in diameter, bent a t 30" angle 2 inches from one end. Glass fiber filter paper KO.x-934-AHJ distributed by H. Reeve Angel & Co., Inc.. 52 Duane St., New York 7, Tu'. Y.
REAGENTS
Eriochrome Black T indicator. Triturate 1.0 gram of Eriochrome Black T with 50 grams of Mallinckrodt anslytical reagent anhydrous granular sodium sulfate in a mortar and pestle until all of the dye is evenly distributed on the surface of the sodium sulfate crystals. Standard magnesium chloride. Dissolve 2.03 grams of reagent grade magnesium chloride hexahydrate in a small volume of water and dilute to 1 liter. Standard lead nitrate. Dilute 3.312 grams of analytical reagent lead nitrate, dried 1 hour a t 110' C., to 1 liter. Standard disodium dihydrogen (ethylenedinitrilo) tetraacetate dihydrate. Dissolve 3.9 grams of the analytical reagent in distilled water and dilute to 1 liter. Standardize against the standard lead nitrate solution using Eriochrome Black T indicator. Buffer. Add 600 ml. of concentrated ammonium hydroxide to 20 grams of analytical reagent ammonium chloride and dilute to 1 liter. Potassium cyanide, reagent grade. Hydroxylamine hydrochloride, reagent grade. Ammonium tartrate, reagent grade. Alcohol, Baker's analytical reagent grade, formula 3-A. PROCEDURE
Pipet 100 nil. of gasoline into the 500ml. extraction flask, record the temperature to 0.5' F., and add a porcelain chip. Add 50 ml. of concentrated hydrochloric acid through the condenser. Adjust the antispattering rod in such a manner that condensate does not flow down it. Reflux for 30 minute5 a t a moderate rate and drain the water from the condenser. Add 100 ml. of VOL. 29, NO. 9, SEPTEMBER 1957
1331
priate corrected volume, V , as given in the ASTAI method section 6b ( 1 ) .
Table I. Tetraethyllead in Gasolinea
Diff. bettTeen Averages
Present Method Found Range AV. 2 479 0 001 2 479 2 478
ASTM Method Found Range
2 480 2 487
0 007
2 483
-0 004
2 833
0 004
2 831
2 828 2 824
0 004
2 826
+O 005
2 834 2 833
0 001
2.834
2 817 2 823
0 006
2 820
+o
1 755 I 751
0 004
1.753
1 766
0 017
1 757
-0 004
2 961 2 965
0 004
2,963
2 947 2 958
0 011
2 951
$0 012
2 951 2 944
0 007
2,947
2 958 2 937
0 021
2 947
0 000
2 817 2 821
0 004
2 819
2 790 2 809
0 019
2 .i 9 9
-0 020
2 384 2 385 2 385
0 001
2 385
2 385
0 004
2.383
+o
2 310 2 319
0 009
2 314
2 315
0 006
2 312
$0 002
1 995 2 000
0 005
1.997
1 992 1 997
0 005
1.995
$0 002
2 038 2 040
0 002
2.039
2 050
0 007
2 046
-0 007
2 829
a
I 748
2 381
2 309
2 043
AV
.
RESULTS
The tetraethyllead content of 11 commercial samples of gasoline was determined by the ASThl lead chromate method (1) and by the proposed method. Comparative results obtained using 100nil. samples are tabulated in Table I. The standard deviations calculated from the duplicate measurements for the ASTX lead chromate and proposed method are 0.006 and 0.002, respectively. for a range of 1.7 to 3.0 ml. of tetraethyllead per gallon. The expected deviation of duplicates from their mean, based on tvr-ice the standard deviation, is 0.012 for the ASTM lead chromate method and 0.004 for the proposed method.
014
002 DISCUSSION
Results in ml. of tetraethyllead/gallon
distilled water to the flask through the condenser and evaporate a t a moderate rate to a volume of 5 to 10 ml. Permit to cool slightly, adjust the antispattering rod to conduct the condensate to the surface of the liquid, and cautiously add 15 ml. of concentrated nitric acid through the condenser. Bfter the initial reaction has subsided, heat moderately until the volume is reduced to 5 to 10 ml. Permit to cool slightly and cautiously add 15 ml. of concentrated sulfuric acid through the condenser. Heat to fumes of sulfuric acid, and continue heating strongly until the flask is clear of fumes. If carbon is still present, add 5 ml. of concentrated nitric acid and repeat the fuming procedure. Cool to room temperature and slowly add 100 ml. of distilled water and 50 ml. of alcohol. Circulate water through the condenser and reflux for 10 minutes. Wash down the condenser with 30 ml. of dilute alcohol (1 2). Let stand until the contents of the flask attain room temperature, but not less than one hour, Decant through glass fiber filter paper. Add 30 ml. of alcohol to the precipitate in the flask, stopper, and shake thoroughly, and filter by decantation, Transfer the filter pad t o the flask, add 0.5 gram of ammonium tartrate, 100 ml. of water, and 10 ml. of buffer. Allow 1 to 2 minutes for the precipitate to dissolve; dilute to about 300 ml. Add approximately 100 mg. of potassium cyanide and an equal amount of hydroxylamine hydrochloride. Add 5.0 ml. of standard 0.02Y magnesium
chloride and 100 mg. of the prepared indicator. Titrate to the permanent blue end point with standard disodium dihydrogen (ethylenedinitrilo) tetraacetate. Stopper the flask, shake vigorously for 1 minute, and complete the titration if the wine red color reappears.
CALCULATIOX.The niilliliters of tetraethyllead per gallon of gasoline a t 60" F. a r t calculated by the follon-ing P q u Rt 1011: '
Tetraethyllead, ml. per gallon = 371(A - B)dV
v-
where
-1.
=
+
1332
ANALYTICAL CHEMISTRY
volume of standard 0.02,V disodium dihydrogen (ethylenedinitrilo) tetraacetate used in the titration
B = volume of disodium dihydrogen
y
=
(ethylenedinitrilo) tetraacetate equivalent to 5.0 ml. of 0 . 0 2 ~ magnesium ~ chloride solution normality of the disodium di'lydrogen
tetraacetate solution of sample, 60" F.
= volume
at
When samples are taken a t temperatures other than 60" F., use the appro-
Direct titration of lead resulting from acid hydrolysis is subject to interferences due to iron from storage containers and dye added to the gasoline for the purposes of identification. Interference due to iron cannot be overcome by addition of potassium cyanide and hydroxylamine hydrochloride when tartrate is present. Dye interferes serioudy with the end point making the wine red to blue color change broad and indistinct. These interferences are overcome by separation of the lead as sulfate in the manner proposed. Lead is separated as the sulfate from all common metals except barium and drontium. Barium sulfate does not interfere and strontium is not likely to be present. LITERATURE CITED
(1) ;im. Soc. Testing Materials, "ASTM Standards on Petroleum Products and Lubricants," Method D 52618T.1948. Ibid.,-b 269-53T, 1955. Banewicz, J. J., Kenner, C. T., ANAL. CHEM.24, 1186 (1952). Banks, J., Analyst 77, 484 (1952). Biedermann, W., Schwarzenbach, G., Chintia (Prague) 2, 56 (1948). Calingaert, George, Lamb, F. ITr., Miller, H. L., Noakes, G. E., -4NaL. CHEM. 22, 1238 (1950). Cheng, K. L., Kurtz, Toubp, Bray, R. H., Zbid., 24, 1640 (1952). Diehl, Harvey, Goeta, C. A., Hach, C. C., J . Am. W a t e r Works Assoc. 42, 40 (1950). Flaschka, H., Mikrochemie ver. Jlicrochim. A c t a 39, 315 (1952). Gehrke, C. W., Aftsprung, H., Lee, Y.. Aiv.4~.CHEW26. 1944 (1954). (11) Jennkss, Robert, Ihid., 2 5 , 966 (1953). (12) llilner, 0. I., Shipman, G. F., Ihid., 2 6 , 1222 (1954). (13) Patton, J., Reeder, W., Ibid., 28,1026 (1956). (14) Wilson, A. E., Ihid., 22, 1571 (1950). RECEIVED for review July 25, 1956. Accepted -4pril26, 1957.
