Rapid Extraction of Manganese(l1) with 2-Thenoyltrifluoroacetone Spectrophotometric Determination in the Organic Phase ANlL K. DE and MD. SYEDUR RAHAMAN Department o f Chemistry, Jadavpur University, Calcutta-32, India
b A new method is proposed for simultaneous extraction and spectrophotometric determination of manganese(l1) a t the milligram level with 2-thenoyltrifluoroacetone. The method is based on the formation of a yellow chelale which i s extractable b y acetone-benzene. The yellow solution follows Beer's law a t 420 mb over the range of 4 to 80 pg. of manganese(l1) per ml. Quantitative extraction occurs in the pH range 6.7 to 8.0. The system i s stable for 48 hours. Silver, lead, mercury(ll), calcium, strontium, zinc, bismuth, aluminum, thorium, zirconium, chloride, sulfate, phosphate, borate, tartrate, and also small amounts of copper, nickel, chromium, and uranium do not interfere. Cobalt(l1) and EDTA interfere seriously. Manganese(l1) can be determined in an iron(ll1)-manganese mixture. The method i s accurate and reproducible to within &2% and compares well with the standard method. The sensitivity i s 0.1 pg. of manganese(I1) per ml.
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T H I S LABORATORY, 2-thenoyltrifluoroacetone (TTA) has been used for extraction and spectrophotometric determination of uranium, iron, copper, cerium, chromium, and cobalt (6, 7 ) . Further studies have been extended t o manganese(I1). With TTA, manganese forms a yellow chelate which is sparingly soluble in benzene but soluble in acetone with the resulting solution extractable by benzene. This is the basis of a new method for rapid extraction and determination of manganese a t the milligram level which is reported in the present paper. Williams and Andes ( l a ) reported the eytraction of manganese a t p H 9 with 8-quinolinol-chloroform. Gentry and Sherrington ( 4 ) and also Bode ( I ) developed this method for extraction a t pH T.5 t o 12.5, providing separation from nickel and aluminum. Diethyldithiocarbamate (2, 3, 9) was employed for the evtraction of manganese from weakly acidic solution. Pyridine (5) and tetraphenylarsonium chloride ( I f ) were used as extractants for permanganate ion in alkaline medium.
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EXPERIMENTAL
Apparatus and Reagents. A Unicam SP-600 spectrophotometer with 1-em. glass cells was used for t h e abiorbance measurements. All t h e pH measurements were done n-ith a Cambridge p H meter. T h e chemicals used were either chemically pure or reagent grade materials unless otherwise mentioned. TTX (Columbia Organic Chemicals, Columbia, S. C.) solutions in acetone (-0.15M) were used. A stock solution of manganese sulfate was prepared b y dissolving about 7.7 grams of the sulfate in 500 ml. of water, ~ 0 . 1 , Vin sulfuric acid. The solution was standardized by the bismuthate method; it contained 4.52 mg. of manganese per ml. Test solutions (180 pg. of manganese per ml.) were prepared b y appropriate dilution of the stock solution. Buffer solutions (1-11) of different p H were prepared b y standard procedures : potassium chloride-hydrochloric acid (pH 1.7 t o 2.8), acetic acidammonium acetate (pH 4 t o 6), and ammonia-ammonium chloride (pH 8.0). General Procedure. A suitable aliquot ( 2 . 5 to 5 ml.) of the manganese
WAVELENGTH
sulfate solution containing 180 pg. of manganese per ml. was mixed with 10 ml. of buffer solution of pH 6.0 in a 250-nil. separatory funnel. For pH studies, the suitable buffer solution of desired pH was used. For the study of diverse ions, the solution containing the foreign ion under investigation was introduced prior to the buffer solution. The aqueous phase was shaken for 2 minutes n i t h 10 ml. of acetone solution (0.15X) of T T A and then for 5 minutes with a mixture of 5 ml. of acetone and 5 ml. of benzene. The layers were allowed t o settle. The aqueous phase was drained into a beaker and the organic phase !vas collected in a 25-ml. volumetric flask. The lattcr \\as diluted to 25 nil. with acetone, a i d the absorbance vas measured a t 420 mp against a reagent blank. The corresponding manganese concentration IT as read directly from the calibration curve described below. The p H of the aqueous layer was measured immrdiately after cxtraction. RESULTS AND DISCUSSION
T h e absorption solution of manchelate (man-
Absorption Curve.
spectrum of a ganese(I1)-TTA
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Figure 1. A Absorption spectrum of manganese(l1)-TTA chelate in acetone-benzene (Mn = 6.6 X 10-4M; TTA = 1.5 X 10-1M; pH = 6.7) vs. reagent blank B Reagent hlank vs. acetone-benzene (TTA = 1.5 X 1 O-'Mj pH = 6.7) VOL. 35, NO. 2, FEBRUARY 1963
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ganese = 6.6 X 10-4M), extracted as above at p H 6.7, is shown in Figure 1 against a reagent blank. The curve shows a peak at 410 my, and after that the absorbance gradually decreases and becomes insignificant beyond 600 mp. The reagent blank shows strong absorption below 410 mp; i t shows appreciable absorption a t 410 mp which becomes relatively negligible from 420 mp onward. For absorbance measurements the region of maximum absorption (410 mp) is avoided because of reagent absorption, and 420 mp is used throughout. The absorptivity at 420 mp is 610.7 h 9.7 and at 410 mp (maximum absorption) is 723.2 i 10.5. Ratio of Acetone to Benzene. As in t h e case of cobalt(II), manganese(11)-TTA chelate is sparingly soluble in benzene b u t highly soluble in acetone. Since acetone is miscible with water, benzene is added t o extract the chelate from the aqueous phase. The optimum acetone to benzene ratio is 16 t o 5 (by volume) for a manganese content 2 1mg. and 15 to 7 for
