(8) MacSevin, W. hl., Kriege, 0. H., Zbid., 28, 16 (1956). (9) hlacSevin, W . M., Kriege, 0. H., J . Am. Chem. SOC. 77, 6149 (1955).
(10) Meyer, J., Kawczyk, $1. Z . anorg. u. allgem. Chem. 226,295 (1936). (11) Stevenson, P. C . , Franke, A. A., Borg, R., Nervik, W.,J . Am. Chem. SOC.75,4876 (1953).
(12) Tuthill, S., Ph.D. dissertation, Ohio State University, 1958.
RECEIVED for review December 10, 1956. Accepted February 11, 1957.
Determination of Calcium or Zinc Additives in Lubricating Oils and concentrates By an (Ethylenedinitri1o)tetraacetic Acid Titration Method P.
B. GERHARDT and E. R. HARTMANN
Products Research Division, ESSO Research and Engineering Co., linden, N. 1.
b A method has been developed for determining calcium or zinc directly in oils without prior ashing of the sample. The sample is mixed in acetone and after the metal has been chelated with EDTA, excess EDTA is titrated with standard magnesium chloride.
I
ORDER to control certain processing or blending operations, petroleum testing laboratories are frequently required to make rapid determinations of calcium or zinc in petroleum products. Although emission spectrographic or flame photometric methods are available, this costly equipment cannot be justified in some operations. Hence, a rapid method of chemical determination of calcium and zinc is often required. A method has been developed which permits determination of calcium or zinc directly in oils without prior ashing of the sample. Essentially, it consists of mixing the sample in acetone and after chelating the metal with (ethylene dinitri1o)tetraacetic acid (EDTA), titrating the excess EDTA with standard magnesium chloride. Although solution is not always complete, the analysis is quantitative. The reactions involved are based essentially on the chelating properties of EDTA (1-3). Because the method requires neither ashing nor precipitation steps, it is extremely rapid. An analysis can be completed in about 20 minutes.
x
REAGENTS
(Ethylene dinitri1o)tetraacetic acid (EDTA), approximately 0.W. This solution does not require standardization. Magnesium chloride, 0.1N. Stand-
ardize by titrating a weighed portion of reagent grade barium chloride in water as described in the procedure, First dry the barium chloride for 2 hours a t 125" t o 130" C. Indicator, Eriochrome Black T. Triturate 0.2 gram of the dye with 100 grams of ammonium chloride and store the mixture in a tightly stoppered bottle. (This mixture is not stable and should be discarded after about 3 weeks.) Buffer solution. Dissolve 67.5 grams of ammonium chloride in about 200 ml. of distilled water, add 570 ml. of concentrated ammonium hydroxide, and dilute t o 1liter with distilled water. PROCEDURE
Weigh an amount of the sample sufficient to contain 20 mg. of metal into a 300-ml. Erlenmeyer flask, and add about 130 ml. of acetone. Swirl the flask until the sample is completely dissolved or well dispersed, When the product under test is an oil blend, the size of sample should be about 10 grams weighed to the nearest 0.1 gram. When it is an additive concentrate, the size should be 0.2 to 0.4 gram, weighed to the nearest milligram. I n some cases a slight cloudiness may persist. This has no effect upon the final result. Into a second flask put the same amount of acetone, but no sample. By means of pipet, add 25 ml. of the 0.1N EDTA solution to each flask. To ensure complete mixing, swirl and warm both flasks at steam bath temDerature for 5 minutes. Cool the flasks slightly and add to each, 2 ml. of concentrated ammonium hydroxide, 10 ml.of the buffer solution, and about 0.3gram of the indicator mixture. Titrate both solutions with the standard magnesium chloride solution to a wine-red end point, Calculate the metal content of the sample by the equation: M = ( B - S) X N X e X 100 W-
where B = volume in milliliters of magnesium chloride solution needed for titration of blank S = volume in milliliters of magnesium chloride solution needed for titration of sample N = exact normality of magnesium chloride solution e = milliequivalent weight for metal insam le W = weight ofsample, in grams M = weight per cent of metal in sample REMARKS
The estimated method is:
precision
yo Level Calcium Zinc
0.5-1.5 0.5 9.0
of
the
Precision
0.020 0.012 0.11
The method has the following limitations: Samples must contain only one bivalent metal; and, it cannot be used for the analysis of used lubricating oils because of interference from iron, lead, copper, etc. When the reagents are added, certain einc products cause the mixture to assume a bluish green color. This does not affect the final result. LITERATURE CITED
(1) Banewics, J. J., Kenner, C. T., ANAL. CHEM. 24 1186 1952). (2) Martell, A. E., alvln, M., "Chemistry of the Metal Chelate Com-
d
pounds," 5th ed., Vol. 1, Van Nostrand, New York, 1952. (3) Schwarzenbach, G., Biedermann, W., Helv. Chim. Acta 31, 456 (1948).
REC~IVED for review June 11, 1956. Accepted March 5, 1957. VOL. 29, NO. 8, AUGUST 1957
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