salting-out agent on extraction of zirconium(1V) with lOOyo mesityl oxide was studied in the acid range of 2.54J1. Their presence in t h e aqueous phase increased t h e extraction of zirconium(IV), because less mesityl oxide is combined with acid and hence more of it is available for the extraction. The optimum concentration of saltingout agent is 4M sodium nitrate in 4M nitric acid. A higher concentration of nitric acid was avoided because of the slight dissolution of the mesityl oxide layer. The extraction of Zr(1V) with 1 0 0 ~ mesityl o oxide was also studied in the acid range of 2.5-4M to determine the effect of varying concentrations (14M)of NH,NOa and NaN03 as the salting-out agent. Mesityl Oxide Concentration. T h e concentration of mesityl oxide was varied from 19 t o rooyo with methyl isobutyl ketone as the diluent. T h e effect of the extraction was noted a t different acidities (Table I) in t h e presence of 4 J I sodium nitrate. Dilution of mesityl oxide lowers the extraction. A plot of log D us. log C
mesityl oxide (Figure 1) a t 3 and 5 M nitric acid indicates slopes of 2.4 and 1.6, showing the extractable species to be Zr(N0-J4 2 M e 0 and H[Zr(h’Os)4(MeO)z], respectively. The system conforms to the limiting square law (1) in the case of zirconium(1V). The optimum reagent concentration is 100%. Diverse Ions. A number of representative ions were tested for interference (Table 11). Lead, thallium, cadmium, bismuth, iron, aluminum, zinc, manganese, cobalt, nickel, uranium, thorium, chloride, and sulfate do not interfere, even if present in the ratio of 1: 5. Ions which can easily form anionic complexes with zirconium(1V) -e.g., oxalate, citrate, ascorbate, E D T A strongly interfere. The tolerance limit ( 2 ) of ions such as copper, cerium, chromium, and palladium can be increased by preliminary extraction of these ions with 2-thenoyltrifluoroacetone ( 4 ) . Interferences due to anions can be eliminated by anion exchange; whereas those due to certain cations can be removed by masking with suitable sequestering agents. The
tolerance limits of the ions are listed in Table IT. From 10 runs with 130 pg., of zirconium(IV), using a general procedure, the average recovery was 96.4 f 1.2% with a standard deviation of 2.0%. LITERATURE CITED
( 1 ) Alcock. K.. Bedford. F. C.. Hardwick. W. H., &lcKay, H. A.’C., J . Inorg. Nucl: Chem. 4, 100 (1957). ( 2 ) Dhara, S. C., Khopkar, S. ST.,Mikrochim. Acta (in press). (3) Dragulescu, C., Simonescu, T., Policec, S., Talanta 11, 747 (1964). ( 4 ) Khopkar, S. hI., De, A. K., J . Scz. Ind. Res. ( I n d i a ) , 21A, 131 (1962). ( 5 ) Morrison, G. H., Freiser, H., ANAL. CHEM.36, 106R, (1964). ( 6 ) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., p. 970, Interscience, New York, 1959.
S. 31.KHOPKAR S. C. DHARA
Department of Chemistry Indian Institute of Technology Bombay 76, India WORKsupported by a financial grant from the Council of Scientific and Industrial Research, India.
Modification of Flask Method of Sulfur Determination Determination of Sulfates with Sulfonazo 111
SIR: The flask method ( 2 ) is the most convenient method for determination of organic sulfur. The modification of this method by Wagner (S), who used titration with barium perchlorate and visual indication with thorin, is considered the best. Airecent investigation ( I ) of the color reaction of sulfonazo I11 [2, 7-bis(0-sulfopheny1azo)chromotropic acid] with barium ions resulted in excellent sensitivity and selectivity. Sulfonazo I11 can also be used for visual indication in the barium perchlorate titration of sulfate ions. Compared to the use of thorin, the end point is much sharper and is unaffected by pH changes. The
Table 1.
Determination of Sulfur in Various Samples
%S
Std. dev., %
Sample Calcd. Founda Chromotropic acid (dihy18 00 17 84 f O 16 drate) 1-Cysteine 26 47 26 41 3ZO 17 Potassium sulfate 18 40 18 40b fO 08 Sulfanilic acid 18 52 18 48 f0 16 Taurine 25 62 25 46 f O 18 Thiosemicarbazide 3 5 . 1 9 35,22 f0,20 Thiourea 4 2 . 1 3 4 1 . 9 7 3ZO.24 Average value from 5 determinations. b Average value from 10 determinations.
reaction should be carried out in a homogeneous aqeuous-nonaqueous solution, because a n aqueous medium permits formation of the sulfonazo 111-barium complex. Water and acetone appear to be the best medium. The aprotic solvent acetone decreases the dissociation of sulfonazo 111, and in this way the formation of the sulfonazo 111-barium complex is hindered. Organic sulfur can also be determined by using the flask method and sulfonazo I11 indicator. EXPERIMENTAL
For combustion and titration, 250-ml. or 300-ml. Schoniger flasks were used. Barium perchlorate (0.01M) was prepared by dissolving 2.37 grams of reagent grade barium perchlorate in distilled water and making up to 1 liter. The solution was standardized by titration with reagent grade potassium sulfate, previously dried a t 110’ C. Sulfonazo I11 (0.1%) was prepared by dissolving 0.1 gram of sulfonazo I11 in 100 ml. of distilled water. This solution is stable for many months. Medical grade oxygen wv~bsused directly from the cylinder, and all other chemicals used were reagent grade. Procedure. A 0.15-ml. sample of 30% hydrogen peroxide and 4 ml. of distilled water are placed in a Schoniger flask. The flask is filled with oxygen, and a 4- to 7-mg. sample is combusted and then absorbed by shaking in the absorption solution for 15 minutes.
The flask is opened, 3 ml. of acetone and 3 drops of sulfonazo I11 solution are added, and the solution is titrated with barium perchlorate solution. The red color of the solution changes sharply to blue a t the end point. A blank solution is unnecessary if Schleicher-Schuel filter paper No. 58g2 is used for the combustion step. For calculations, 1 ml. of barium perchlorate solution is the equivalent of 0.32066 mg. of sulfur. Other salts, such as potassium chloride and sodium perchlorate, interfere when present in excess of 0.1 mmole. Primary potassium phosphate interferes in excess of 0.01 mmole. RESULTS
Typical results from the determinations are given in Table I. Work in this laboratory indicates that the titration can be used for the determination of inorganic sulfur if a quartz combustion tube and a spiral absorber are used in place of the Schoniger flask. LITERATURE CITED
( 1 ) BudBBinsk9, B., Yrzalovit, D., Z. Anal. Chem., 210, 161 (1965). ( 2 ) Schoniger, W., Zbid., 181, 28 (1961). (3) Wagner, H., Mikrochim. Acta ( W i e n ) 1957, p. 19.
BRETTSLAV BCDESINSKY Department of Analytical Chemistry Xuclear .Research Institute Czechoslovak Academy of Sciences Rzhezh near Prague, Czechoslovakia VOL. 37, NO. 9, AUGUST 1965
1 1 59
