Spectrophotometric Titration of Milligram Quantities of Barium KEITH ROWLEY, R. W. STOENNER, and LOUIS GORDON Departments of Chemistry, Brookhaven Nations/ Laboratory, Upton, Long Syracuse University, Syracuse 70, N. Y.
/sfand, N. Y., and
The detection of the end point is difficult in the complexometric titration of small amounts of barium with disodium dihydrogen ethylenediaminetetraacetic acid using Eriochrome Black T as indicator. A method is described for the determination of barium which utilizes a spectrophotometric detection of the end point. The method is capable of determining 0.1 to 5 mg. of barium by titration with 0.01 to 0.001N EDTA at a wave length of 650 nip.
ANNS, Reschovsky, and Certa (3) have published a titrimetric method for barium in which 500 mg. of barium acetate was titrated with 0.lX disodium dihydrogen ethylenediaminetetraacetic acid [disodium dihydrogen(ethy1enedinitri1o)tetraacetic acid, EDTA 1. The concentration of dye nsed by these investigators was such that under tungsten illumination a color change from wine-red to almost colorless was observed a t the end point. T h e application of this procedure by others (4,5 ) to smaller amounts of barium has indicated the use of more dilute titrant and additional dye in order t o detect the end point'. Under these conditions the color change is extremely difficult t o detect, as the solution is tit,rated until the last trace of wine-red color disappears leaving a clear blue color. The elimination of this visual difficulty by utilizing a spectrophotometric detection of the end point is described in the present paper. I n addition, this technique permits the determination of much smaller quantities of barium than is possible with the visual method.
0.I
I
0
1
2
Figure 1.
3
4 5 6 7 ML. EDTA SOLUTION
9
Spectrophotometric titration curves
Table I.
Determination of Barium
Ba-Taken,
Difference (Found Minus Taken),
hlg.
0 10 0 49 0 99 4 94=
8
blg.
o.oo,o.oo,0.00
+ 0 . 0 1 , 0 . 0 0 , 0.00, -0 02 -0.01, -0.01, -0.01, -0.01, -0.01 0 00, +0.04, + 0 . 0 6 , + 0 . 0 3 a Titrated n i t h 0 00913.V E D T A ; all other titrations with 0 00183N EDT.1.
MATERIALS USED
EDT.l solutions. A 0.01S solution was prepared according t,o the directions of hlanns, Reschovsky, and Certa ( 3 ) )except for appropriate reductions in the quantities of reagents required. This solution was standardized by the titrimetric procedure given below against a barium solution which had been previously standardized by a gravimetric procedure. --I0.002.l.i EDTA4solution was prepared from the 0.0LV solution by dilution. The buffer solution was also prepared according to directions of Manns ( 3 ) . Eriochrome Black T. Fifty milligrams of the dye (Hart,manLeddon Co., Philadelphia, Pa.) were dissolved in 50 ml. of triethanolamine ( 1 ) . Titrat,ion apparatus. A Coleman rniversal instrument, Model 14, was used with a rect,angular titration cell of 75-m1. capacity with a 5-cm. light path. -1small propeller-type glass stirrer and a bent glass tube which hooked on to the cell and could be used t o furnish a blanket of nitrogen t,o exclude carbon dioxide completed the cell assembly.
itself was found to occur at' 650 mp. This is in agreement with data by Harvey, Komarmy, and Wyatt ( 2 ) . Data obtained a t this wave length in the titration of milligram quantities of barium are shown in Table I. Typical titration curves are shown in Figure 1. The absorbancy readings were not corrected for volume changes in the solution. A reagent blank correction of 0.14 ml. was deducted when the 0.001835 EDTA solution Jvas used. The blank was negligible in the case of the 0.009135 solution. Several titrations with 50-mg. quantities of barium and 0.1-1-EDT.4 indicate the feasibility of determining larger amounts of barium; in four titrations the volumes of titrant were 6.98, 6.98, 7.03, and 7.OG ml. I n the titration of this large quantity of barium it is necessary to blanket the solution with nitrogen t o prevent the precipitation of barium carbonate.
PROCEDURE
Take for analysis a sample which contains from 0.1 to 5 mg. of barium in 15 to 20 ml. of solution which should be neutral or slightly acid and carbonate-free. -4dd in the follo~vingorder: 5 ml. of methanol, 10 ml. of buffer, and 5 drops of the indicator dye to the titration cell. Adjust the stirrer so that it is above the light path,and so that the solution is agitated without the appearance of air bubbles; make sure that the solution contents are thoroughly mixed before the titration is begun. Titrate with a solution measuring the absorbancy a t 650 mp. standard EDTA% Use 0.002.V EDTA solution for the titration of less than 1 mg. of barium; for larger amounts use 0.01S titrant. Obtain the end point from a graph of milliliters versus absorbancy. Determine a reagent blank correction from a similar titration in the absence of barium.
ACKNOWLEDGMENT
One of the authors (L. G.) gratefully acknowledges the support of the Atomic Energy Commission under Contract AT(30-1)-1213 with Syracuse University. LITERATURE CITED
(1) Diskant, E. M., ANAL.CHEM.24, 1857 (1952). ( 2 ) Harvey, A. E., Komarmy, J . 31.,and Wyatt, G. 31., Ibid.,25, 498 (1953). (3) llanns, T. J., Reschovsky, R I . U., and Certa, A. J., Ibid.,24, 909 (1952). (4) Reimer, C.. doctoral thesis, Syracuse University, 1953. (5) Sijderius, R., Anal. Chim. Acta 10,517 (1954).
RESULTS AND DISCUSSIOK
RECEIVED for review December
30, 1964. Accepted October 26, 19.55. Work carried o u t under the auspices of the C . S. Atomic Energy Commission.
The maximum difference between the absorbancy of the magnesium complex with Eriochrome Black T dye and the dye
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