V O L U M E 25, NO. 12, D E C E M B E R 1 9 5 3 By isolation of the silver-silver chloride electrode in a separate compartment, which makes electrical contact with the solution being titrated by means of a liquid-liquid junction through a ground-glass sleeve (see Figure 3), the reversal in the e.m.f. curve is eliminated and a normal titration curve is obtained (see curve B, Figure 2). The silver-silver chloride electrode used is one that is readily available commercially. The liquid in the isolation compartment is the same solvent as used for the sample-i.e., glacial acetic acid--but it is saturated with potassium chloride to increase its conductivity. So far approximately 100 continuous automatic titrations have been made without difficulty using the silver-silver chloride electrode isolated in the separate compartment. The observed e.m.f.’s are essentially reproducible and thus permit the shuttingoff of the automatic titration apparatus by means of a relay operated by the Brown recorder-controller.
1917 ACKNOWLEDGMENT
The writer wishes to thank Joy S. Wolfarth for making the titration with the Macbeth titration-pH meter. LITERATURE C I T E D
(1) Fritz, J. S., “Acid-Base Titrations in Non-Aqueous Solvents,”
Columbus, Ohio, G. F. Smith Chemical Co., 1952. (2) Fritz, J. S.,ANAL.CHEM.,22, 1028-9 (1950). (3) Ibid., 24, 306-8 (1952). (4) Fritz, J. S.,and Keen, R. T., Ibid., 24, 308-10 (1952). (5) Katz, M., and Glenn, R. A,, Ibid., 24, 1157-63 (1952). (6) Narkunaa, P. C., and Riddick, J. A , , Ibid., 23, 337-9 (1961). (7) Moore, R. T., et al., Ibid., 23, 1639 (1951). (8) Pifer, C. W., and Wollish, E. G., Ibid., 24, 300-6 (1952). (9) Seaman, I+‘., and illlen, E., Ibid., 23, 5 9 2 4 (1951). (10) TS’ittman, G., Angew. Chem., A60, 330-3 (1948). RECEIVED for review hlay 26, 1953.
Accepted July 29, 1983.
Photometric Determination of Copper in Gasoline J. K. LIVINGSTONE AND N. D. LAWSON Petroleum Laboratory, E. I . d u Pont de Nemours & Co., Inc., Wilmington, Del. appears in gasoline in very minute quantities, usC ually less than 0.5 mg. per liter and, because of its pro-oxidant effect, is detrimental to gasoline stability. In order to handle the OPPER
problem of copper contamination of gasolines intelligently, it is necessary to be able to measure accurately the amount of copper present. A revien of the literature reveals that only a few methods deal with the determination of copper in gasoline. A qualitative test was described several years ago ( 4 ) . Another method ( 5 ) , designed for the estimation of copper in gasoline by visual matching of yellow copper diethyldithiocarbamate solutions, was adapted later ( 2 ) for use with a photoelectric colorimeter but is not sufficiently sensitive or accurate for many purposes. This appears to be due principally to incomplete extraction of the copper from the gasoline and the high transmittancy range a t R hich measurements are made. A rapid photometric method for the quantitative determination of copper in gasoline has been developed that is applicable to concentrations of 0.025 to 5 mg. of copper per liter of gasoline with an accuracy within 10% when using a 200-ml. sample of gasoline. I t was found during the development of this method that the normality of the hydrochloric acid solution had a considerable effect on the completeness of the extraction of the copper from the gasoline. I t was found that 0.1A‘ acid removed the copper much more readily than the 4.V acid recommended in earlier methods The use of multiple extractions also improved the recovery of the copper. Furthermore, if the transmittance measurements were made on solutions of the copper complex in an organic solvent such as carbon tetrachloride, as suggested by Sandell ( S ) , more consistent re.sults were obtained. The use of chloroform to remove residual color from the alkaline solution of copper is an improvement over the use of the previously recommended tert-amyl alcohol, as chloroform does a more effective job. Throughout the method the transferring of the solutions containing the copper from one container to another is minimized in order to reduce the possibility of the loss of copper. APPARATUS
The tranmnittarice measurements were made with a Lumetron Model 402-E photoelectric colorimeter equipped as follows: Picture projection lamp, G.E. T-8, 100-watt. Filter, monochromatic, narrow band, No. 440 (transmittance peak = 440 mp). Absorption cell, 50 mm., 70-ml. capacity. (Any change in
light path from the 50 mm. used here will result in changes in precision and accuracy.) REAGENTS
Hydrochloric acid, 0.1N. Dilute 8.3 ml. of concentrated hydrochloric acid (37%) to 1000 ml. with copper-free water, double-distilled from glass distillation apparatus. Sodium diethyldithiocarbamate solution. Dissolve 1 gram of sodium diethyldithiocarbamate in copper-free water, doubledistilled from glass distillation apparatus, and dilute to 1000 ml . Standard copper solution for preparing the standard curve (1 ml. = 0.005 mg. of copper). Dissolve 1.9645 grams of C.P. copper sulfate pentahydrate ( C U S O ~ ~ ~ Hwhich ~ O ) ,contains 0.50 gram of copper, in copper-free water, double-distilled from glass distillation apparatus, and dilute to 1000 ml. Dilute a 10-ml. aliquot of this solution to 1000 ml. Ammonium hydroxide, concentrated, C.P. (28% minimum). Chloroform, C.P. Carbon tetrachloride, C.P. C.P.
PROCEDURE
Extraction with Acid. Pipet 200 ml. of the gasoline to be tested into a 500-ml. separatory funnel and add 30 ml. of 0.1N hydrochloric acid. Shake the solution vigorously for 3 minutes,
Table I.
Recovery of Copper Added to Iso-octane Copppr”, Ilg.
Added t o 200 ml. of iso-octane b
Found in final 100 rnl. of of CCh solution
0,005 0,005
0.005 0.005
0.025
0.028
0.025 0.025
0.050 0,050
0.051
0.050
0.050
0.050
0.051
0.075 0.075
0.074 0.074
0.050
Copper-%ethyl hexoate (C~sHrno~Cu), assay 17.46% copper, dkeolved in acetone t o obtain gasoline-soluble copper standard. b Iso-octane (2,2,4-trirnethyl pentane) treated with three 30-rnl. portions 0.1N HC1 before copper addition.
ANALYTICAL CHEMISTRY
1918 Table 11. Precision
Blank
95.8 95.8
Absorbance 0.019 0.019
Sample (gasoline contaminatedwithcopper by addition of copper2-ethyl hexoate t o 3 liters)
42.1 42.6 42.2 42.0 41.9 41.7
0.376 0,371 0.376 0.377 0.378 0,380
.4verage Repeatability
42.08 0 52
... ...
% T
Operator A Minus absorbance of blanh
Catalytically cracked, gssoline B Straight-run. gasoline C
0.203 0.199 0.202 0.204 0.204 0.205
42.4 41.9 42.5 82.2 42.5 42.3
0.373 0.378 0 372 0,375 0,372 0.374
0.362
0.0407 0.0411 0.0407 0.0409
0.203 0.357 0.0405 0.005 0.0007 0.W4 Grand average, mg. copper/liter Reproducibility, mg. copper/liter
42.3 0 4 0.204 0.005
... ...
0 362 0.004
0.0006
0.357 0.352 0.356 0.358 0.359 0.361
0.0405 0.0398 0.0403 0.0407 0.0408 0.0410
Copper Found, Mg./Liter 0.02 0.22
...
0.02 0.22
...
0.01 0.20
...
0.01 0.22
0.20 0.20
Aviation, gasoline D ~~
...
0.20
~
Table IV.
Effect of Various Substances Material Added
Copper Taken, MgJLiter
Description
m./ liter 700“ 1 2
13156 0.050 0.050
0.050 0.050 0,050 0.050 0.050 0.050
0,060 a
b c
Tetraethyllead N N’-disalicylidene-l,2-diaminopropane NLbutyl-paminophenol N,N’-di-8%-butyl-p-pbenylenediamine 2 6-di-tert-butyl-4-methylphenol D u Pont o i l Yellow N Du Pont Oil Orange Du Pont Oil Red Du Pont Oil Blue A
Mg.
copper/ 100 ml. CCli
... ...
... ...
cc1k ... ...
Copper Found. hZg./Liter 0,050 0.050 0.023
0.050
2191 c 140 70 70
0.051 0,050 0.051 0.051
350 70 70 70 70
0.050 0.050 0.050 0.050 0.050
covpei I liter
Operator B Minu absorbance of blank
7oT 97.2 97.2
Copper Added (as Hexoate), Mg./Liter 0.20
AIg.
Absorbance 0.012 0.012
Table 111. Analysis of Different Types of Conimercial Gasolines Sample Thermal reformed, gasoline A
-
Mg. copper/ 100 ml.
... ... 0.361 0 366 0.360 0.363
0.360
0.0408 0 0414
0.204 0.207 0.204 0.206 0.204 0.205
0.0409
0.205 0 002
If a satisfactory reading is not obtained by this means, repeat the analysis using a smaller sample of gasoline. 4 blank should be run daily and with each new supply of reagents. Det’ermine the blank by starting with 90 ml. of 0.1-V hydrochloric acid and proceeding as outlined under “Development of Color.” Convert the per cent transmittances obtained to absorbance (log 100/T). Subtract the absorbance of the blank from the absorbance of the sample atid read the milligrams of copper equivalent to the corrected absorbance from the standard curve. Standard Curve. Prepare the standard curve by adding various volumes of the standard copper solution to 90 ml. of 0.lK hydrochloric acid and analyzing as outlined above. Then plot the absorbance against milligrams of copper in the final 100 ml. of carbon tetrachloride. Concentration Range and Accuracy. Inspection of a standard curve indicates that the system conforms to Beer’s law since the standard curve is a straight line. When per cent absorbtancy is plotted against logarithm of concentration ( I ) , the concentration range for best accuracy for the conditions and technique used is 0.027 to 0.074 mg. of copper in the final 100 ml. of carbon tetra’ abchloride; in this range the relative analysis error is 3 % per 1% solute error in transmittancy. The relative analysis error will not exceed 10% in the concentration range of 0.005 to 0.098 mg. of copper in the final 100 ml. of carbon tetrachloride. Precision. The expected limit of deviation of test results from their mean value based on data in Table I1 is:
0.10 weight %.
3 ml./gallon. 5 ml./gallon.
allow to settle, and drain the lower layer into a 500-ml. separatory funnel. Repeat the acid extraction for a total of three times Removal of Residual Color. Pipet 5 ml. of concentrated ammonium hydroxide into the second separatory funnel and swirl to mix. Remove any residual color in the alkaline solution by treating with successive 40-ml. ortions of chloroform until the the chloroform extractions aqueous layer is colorless; then ~ l l o w with one 40-ml. carbon tetrachloride wash. Discard the chloroform and carbon tetrachloride layers. Development of Color. Pipet 10 ml. of sodium diethyldithiocarbamate solution into the separatory funnel and swirl to mix. Add 40 ml. of carbon tetrachloride and shake the solution vigorously for 2 minutes. Allow the solution to settle and drain the lower layer into a 100-ml. volumetric flask. I d d another 40 ml.of carbon tetrachloride to the separatorg funnel and shake the solution vigorously for 1 minute. Allow the solution to settle and drain the lower layer into the 100-ml. flask, make up to volume (100 ml.) with carbon tetrachloride, and mix the solution well. Fill a 70-ml (50-mm.) absorption cell with solution from the flask and determine the per cent transmittance nithin 5 minutes (the solutions gradually became darker on standing in the open absorption cell, owing to evaporation of solvent) at a wave length of 440 mM, the Lumetron having been balanced a t 100yo transmittance against carbon tetrachloride. If the yellox\. carbon tetrachloride solution is too dark in color and does not give a reading on the standard curve, dilute an aliquot of not less than 10 ml. with chrbon tetrachloride and make up to 100 ml
lfg
coppel/ liter
Mg. copper in final 100 ml. CClr hlg. copper per liter (200-ml. sample) % transmittance
Repeatability 0.0008
Reproducibility 0.0012
0.004
...
0.8-0 6
0.006
St’atistical analysis of the data obtained in establishing precision shows the standard deviation to be 0.0025 nig. of copper per liter. This method is satisfactory for the analysis of different type? of fommercial gasolines as is illustrated in Table 111. Sulfur up to a t least 0.1 weight ’%as dibutyl disulfide and tetraethyllead up to at least 5 ml. per gallon do not interfere in this method. Iron naphthenate a t 1 mg. per liter of iron did not interfere in the method, but at 2 nig. per liter it gave high results. Gasoline additives (such as antioxidants, deactivators, and dyes) at normal dosages also do not interfere (Table IT-). LITERATURE CITED
..lyres, G. H., AXAL.CHEM.,21, 652 (1949). ( 3 Roebuck, -4.B.,“Storage Stability of .Aviation Gasoline in Copper Flashed Drums,” S a w 1 Reseal ch Laboratory, R e p t . P-2329 (July 12, 1944). ( : 3 ) Sandell, E. B., “Colorimetric Deterniination of Traces of I\letals,” p. 304, 2nd ed., Ken- York, Interscience Publishers, 1950. (4) Short, G. H., and Schulze, W. A , , Natl. Petroleum News, 31, 162-3 (1939). (5) Universal Oil Products Co., Chicago, “Laboratory Test Method. for Petroleum and Its Products,” 3rd ed., H-39,1947. i,l)
RECEIVED for review January 7, 19Z3.
.\ccepted
-illgust 6 , 1953
