trations of certain salts. Turbidity can usually be removed by ether extraction. If hemolysis is present, a correction can be applied if the hemoglobin concentration is known. Interferences produced by ammonium, sulfate, and sulfite ions apparently vary with the particular biuret technique employed, presumably because of different final concentrations of copper and alkali. LITERATURE CITED
(1) Bing, F. C., Baker, R. K., J . Biol. Chem. 92,589 (1931). 12) Fine, J.. Biochem. J . 29. 799 119351. (3) Goa,' J:, Scand. J . &in. & Lab. Inaest. 5 , 218 (1953). (4) Ibid., 7,Suppl. 22 (1955).
( 5 ) Gornall, 9.G., Bardawill, C. J., David, PVI. bI., J . Biol. Chem. 177,
751 (1949). (6) Henry, R. J., Golub, 0 J., Sobel, C., Clin. Chem., 3,49 (1957). (7) Keyser, J. W., Vaughn, J., Biochem. J . 44, xxii (1949). (8) Kingsley, G. R., J . Biol. Chem. 131, 197 (1939). 19) Ibid.. 140. lxix 11941). (10) Kingsley,'G. R:, J . Lab. Clin. X e d . 27,840 (1942). (11) Kingsley, G. R., Behrend, A . A , , Zbid., 34, 11178 (1949). 112) Kinaslev, G. R.. Machella.' T. E., 1&d.,"34, 1183 '( 1949). (13) Kingsley, G. R., Terzian, L. A,, Zbid., 34, 1175 (1949). (14) Levin, R., Brauer, R. W.,Ibid., 38,474 (1951). (15) Narver, I-L., S c a d J . Clin. & Lab. Invest. 7,Suppl. 21 (1955).
(16) Mehl, J. W.,J . Bid. Chem. 157, 173 (1945). (17) Llehl, J. R., Pacovska, E., Winzler, R. J., Zbid., 177, 13 (1949). (18) Reinhold. J. G.. "Standard hlethods of' Clinicil Chemistry," 5'01. I, p. 88, rlcademic Press, New 1-ork, 1953.
(19) Reinhold, J. G., Bluemle, L. W., Jr., Campoy, F., Gilman, L., Gould, E. F., Martens, V. L., Shuman, R., Federation Proc. 8, 242 (1949): (20) Robinson, H. W,,Hogden, C. G., J . Bid. Chem. 135,707 (1940). (21) Ibid., p. 727. (22) Rosenthal, H. I,., Kawakami, T., Am. J . Clin. Pathol. 26. 1169 (1956). (23) Weichselbaum, T. E., Zbid., 16, 40 (1946). RECEIVEDfor review October 29, 1956. Accepted 3Iay 9, 1957.
Determination of Sulfoxides R. R. LEGAULT and KERMIT GROVES Department of Agricultural Chemisfry, State College of Washington, Pullman, Wash.
b A modified Barnard and Hargrave method has been developed for determination of sulfoxides that yield water-soluble sulfides upon reduction with the titanium trichloride reagent. The interfering sulfides are removed b y extraction with 1 -butanol after partial saturation of the aqueous phase with ammonium sulfate. Final titration with potassium dichromate is carried out as in the original method.
B
Hargrave ( 1 , 2) have developed a method for the determination of sulfoxides based on the reduction of the sulfoxide to sulfide by titanium trichloride. The method involves heating a mixture of the sulfoxide, acetic acid, and a standard solution of titanium trichloride under nitrogen, adding a measured amount of ferric alum to oxidize the excess titanium trichloride, and titrating the ferrous ion with potassium dichromate. Carbon tetrachloride is added before the titration to remove the formed sulfide from the aqueous layer and thus prevent its reoxidation to sulfoxide. This method gives good results with many sulfoxides, but failed when applied to 2-hydroxydiethyl sulfoxide (3) and dimethyl sulfoxide. These sulfoxides gave low and erratic results, and seemed to interfere with the indicator, diphenylaminesulfonic acid. The carbon tetrachloride did not remove the sulfide completely from the aqueous phase before the titration with dichromate. Several extraction procedures for the removal of the sulfide were tried. The
method was modified by eliminating the acetic acid from the reduction step, as acetic acid tended to make the sulfides more water-miscible. Partial saturation of the mixture with ammonium sulfate and extraction with 1-butanol, followed by carbon tetrachloride, successfully removed the sulfides. The modified method gave good results with 2-hydroxydiethyl sulfoxide and dimethyl sulfoxide. REAGENTS
A R ~ A R Dand
Titanium trichloride solution, 0.1N. Mix 100 ml. of 15% titanium trichloride solution with a previously boiled mixture of 50 ml. of concentrated hydrochloric acid and 850 ml. of water. The solution is stored in a bottle protected by a chromous acid solution in a washing tower, and connected to dispense directly to a buret. The solution is standardized by the procedure used for sulfoxide analysis. Ferric alum solution. Dissolve 200
Table 1.
Determination of Sulfoxides
Sulfoxide. R Barnard PVTdm method method I
Compound 2-Hydroxy-
I
Y
diethyl sulfoxide 88zk6 100.4zk0.7 Dimethyl sulfoxide S8zk6 99.7f0.5 Diethyl sulfoxide 99.8&0.7 Dipropyl sulfoxide 94.910.6 92.110.7 Dibutyl sulfoxide 9S.OzkO.7 9 7 . 7 d 0 . 7
grams in 1 liter of water containing 60 ml. of concentrated sulfuric acid. Potassium dichromatesolution, 0.05A'. Dissolve 2.4518 grams of the reagent grade salt in water and make to 1 liter. Phosphoric acid solution. Dissolve 75 ml. of orthophosphoric acid (85%) in 350 ml. of water and 75 ml. of concentrated sulfuric acid. Diphenylaminesulfonic acid indicator, 0.25% aqueous solution. Nitrogen. Pass through a solution of chromous acid (4). Ammonium sulfate solution, saturated a t room temperature. PROCEDURE
Weigh a sample of 0.7 t o 1.0 meq. into a 250-ml. flask equipped with a standard ground joint and a stopper fitted with a three-way stopcock assembly which permits evacuation and filling with nitrogen. Evacuate the flask to about 20-mm. pressure and then fill with nitrogen t h a t has been washed with chromous acid solution to remove tracesof oxygen. Add 15 nil. of 0.1N titanium trichloride solution to the nitrogen-filled flask under a stream of nitrogen. Then evacuate the flask and fill with nitrogen three times in the manner described above. Heat the flask and contents in a bath a t 80" C. for 1 hour. At the end of the hour, add to the flask a boiling mixture of ferric alum and ammonium sulfate solutions, prepared by adding 5 ml. of ferric alum solution to 40 ml. of saturated ammonium sulfate and heating the mixture to boiling. Allcw the solution to stand 30 seconds; then cool rapidly. Add 10 ml. of phosphoric acid solution to the flask. Then transfer the contents of t h e flask to a separatory funnel, extract t h e VOL. 29, NO. 10, OCTOBER 1957
1495
mixture twice with 15-ml. portions of 1-butanol, and follow with three extractions with 15-ml. portions cf carbon tetrachloride, discarding the organic solvent layer. The last portion of carbon tetrachloride need not be separated. Transfer the aqueous phase to the original Erlenmeyer flask, dilute with 55 ml. of water (use portions of the water to complete the transfer), and titrate with 0.05X potassium dichromate solution, using diphenylaminesulfonic acid indicator. Carry out a blank determination in the same manner, omitting the sample.
yo sulfoxide = (blank - titer) X A; dichromate X M . R . sulfoxide X 100 2000 X grams of sample RESULTS
The results of the determination of 2-hydroxydiethyl sulfoxide and some other sulfoxides ( 3 ) by Barnard’s method for saturated sulfoxides, and by the modification of this method, are shown in Table I. LITERATURE CITED
(1) Barnard, D., Hargrave, K. R., Anal. Chim.Acta 5 , 476 (1951).
(2) Ibid., p. 536. (3) Groves, Kermit, Legault, R. R., unpublished manuscript. (4) Treadwell. F. P.. Hall. W.T.. “Analytical Chemistry,” kol. 11, p. 699, Wley, Yew York, 1947. RECEIVED for review February 5, 1957. Accepted May 27, 1957. Portion of a paper delivered before Analytical Chemistry Section, ACS, Seattle, Wash., June 11, 1956. Investigation supported in part by funds provided for biological and medical research by the State of Washington Initiative Measure No. 171. Scientific Paper No. 1575, Washington Agricultural Experiment Stations. Work conducted under Project No. 1229.
Determination of Sulfur in Titanium MAURICE CODELL, GEORGE NORWITZ, and CHARLES CLEMENCY Pitman-Dunn laboratories, Frankford Arsenal, Philadelphia, Pa. Sulfur in titanium and titanium alloys can b e determined by dissolving the sample in a mixture of hydrochloric and hydrofluoric acids. The evolved hydrogen sulfide i s absorbed in ammoniacal cadmium chloride, which is then acidified and titrated with standard potassium iodate solution.
investigations have recently shown that sulfur may become an important alloying element for titanium because it produces grain refinement and increases the tensile and yield strength of titanium (4). It is not known in what form sulfur is present in titanium, although the titanium-sulfur system has been studied (f2,16). I t is certain that the sulfur is not present as elemental sulfur. The following titanium sulfides are known to exist: Ti& Tis. Ti&, Ti&, and TIS, (16). ETALLURGICAL
POSSIBLE METHODS
The first approach to the problem was to attempt to develop a barium sulfate precipitation method, because such a method is usually considered to be the referee method. Experiments were conducted with a 2.5-gram sample of titanium. However, it was not possible to determine sulfur in titanium gravimetrically by barium sulfate precipitation for the following reasons. Titanium inhibited the precipitation of barium sulfate. No precipitate a t all could be obtained if less than 0.1% sulfur were present. The authors believe that the solvent action of the titanium is probably due to the formation of the complex titanium sulfate ion, [Ti(S04)3]-- (3.4). Titanium ap1496
ANALYTICAL CHEMISTRY
parently resembles chromate, which interferes by forming a complex chromium sulfate ion (22, 37). The experiments on the precipitation of the barium sulfate were carried out using the minimum amount of hydrochloric acid (20 ml. of acid per 200-ml. volume) that could hold 2.5 grams of titanium in solution. The solutions were allowed to stand overnight a t room temperature. They could not be heated without causing hydrolysis of titanium. It is probable that the amount of hydrochloric acid used also had a solvent action on the barium sulfate. Recoveries were no better with solutions containing a smaller amount of acid and fluoride, tartrate, or citrate to complex the titanium. The addition of hydrogen peroxide seemed to help the precipitation of barium sulfate slightly. There were no satisfactory separations of the titanium from the sulfur that would permit the subsequent application of the barium sulfate method. The Meineke method by which steels (.2?5>29) and copper-base alloys (11) are dissolved in a 5% hydrochloric acid solution containing cupric ammonium chloride and the precipitated copper sulfide filtered off, is not applicable to titanium because the cupric ion in dilute hydrochloric acid exerts a passivating action on titanium and prevents its solution (7). The separation of 2.5 grams of titanium from sulfate by the use of cupferron did not seem feasible. Precipitation of titanium by hydrolysis -for instance, by fuming with perchloric acid-has, according to experience in this laboratory, proved valueless when applied to the separation of large amounts of titanium from any element. An ammonium hydroxide or
sodium hydroxide precipitation might be satisfactory for the separation of only small amounts of titanium. Ullrich (36) used an ammoniacal separation in the determination of sulfur in titaniferous coals containing about 4% titanium. The best separation of titanium from sulfate is no doubt the ion exchange method (28, $1). However, it too did not seem too feasible for the separation of 2.5 grams of titanium. The titanium metal could not be dissolved in a satisfactory oxidizing medium for the gravimetric determination of sulfur. Konoxidizing solvents could not, of course, be used because sulfur would be lost as hydrogen sulfide. The following oxidizing media n 111 not dissolve titanium: nitric acid, bromine, a mixture of nitric acid and bromine, a mixture of nitric and hydrochloric acids, and a mixture of hydrochloric acid and hydrogen peroxide. Fuming nitric acid attacks titanium but the reaction may be explosive. The only oxidizing medium that could be used was 3 mixture of hydrofluoric and nitric acids, or a mixture of hydrofluoric acid and hydrogen peroxide. Both the hydrofluoric acid and nitric acid 1%ould be objectionable because the fluoride and nitrate could contaminate the barium sulfate precipitate. Decomposition of a 2.5-gram sample by fusion with sodium peroxide or mixture of sodium carbonate and potassium nitrate did not seem practical. Because the barium sulfate precipitation method showed no promise, efforts were turned toward other procedures. Luke (23) has proposed a method for the determination of sulfur in many alloys whereby the sulfur is converted to sulfate, which is then reduced t o
