acid reaction, with the polar dye molecule serving BS the reference soft baw.
lytic Conductance,” p. 228, Interscience, N. Y., 1959. (4) Fuoss, R., Onsaaer, L., J . Phus. Chem. 67, 621 (1963). (5) Grunwald, E.,Winstein, S., J. Am. Chem. Soe. 70, 846 (1948).
UTERATURE CITED
(6) Kirkwood, J. G., J . Chem. Phys. 2 , (I) Brooker,L.G.S.,etd.,J.Am.Chem. 351 (1934). Soc. 87, 2443 (1965). (7) Kolling, 0. W., Tmm. Ram. A d . (2) Dsvq M. M., Hetzer, H., ANAL. Sei. 68,575(1965). CHEM.38, 451 (1966). (8)Kosower, E. M., J . Am. Chem. Soe. (3) Fuos, R., Accascins, F., “Electro80, 3253 (1958).
(9) McRse, E. G.,J . Phys. Chem. 61, 562 (1957). (10) Peanon. R. G..J . Am. Chem. SO^. 85,3533 (1963). ‘ (11)Voigt, E.M.,J . Phys. Chem. 70, 598 (1966). ORLANDW.KOLLINQ
Chemistry Department Southwestern College Winfield, Kan. 67156
Effects of Varying Tin(ll) and Bromide Concentration in the Spectrophotometric Determination of Irid ium SIR:The yellow color formed by the reaction between tin(I1) and iridium salts in a bromide medium has been suggested for the spectrophotometric determination of iridium. Berman and McBryde (1) report a molar absorptivity of 4.96 X lo4at 402 mfi but Pantmi and Piccardi (2) report 2.5 X lo4 at 403 mp. Our results support a value in the range of (4.5 to 5.5) X 10‘. Tertip tis and Beamish (5) satisfactorily described the optimum conditions for the determination of iridium by this method after extraction of rhodium by isopentyl alcohol. Because both the concentration of bromide and of tin(I1) should exert considerable influence, we have examined the effect of these two variables in detail. EXPERIMENTAL
Reagents. Bromine - free hydrobromic acid was prepared by distillation over red phosphorous. Stannous bromide was prepared by dissolution of tin in hydrobromic acid. Chloroiridic acid was supplied by the J. Bishop & Co. Platinum Works, Malvern, Pa. Stannous fluoroborate, 29 to 31% solution w./v. Sn, was obtained from Hopkins and Williams Ltd., Chadwell Heath, Essex, England. Perchloric acid was reagent grade
4
2 0.30 0
0.10
0.00
1
I
0.50
1.00 1.50 [R -1
I
I
9.00
9.50
Figure 2. Effect of Br- on the absorbance at 403 mp of a solution 1.30 X 1 0-DMin HzlrCls and 1.3 X 10-’M in Sn(BF4)z held at constant acidity and ionic strength of 2.7M 1.00-an. path length
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ANALYTICAL CHEMISTRY
0.60
c \
0.40
-
0.10
1
350
375
1 400 Wml.n&,
I
I
I
495
450
475
DW
Figure 1. Spectral curves showing the effect of Br- on a solution 1.30 X 10-6M in H K l s and 1.3 X 1 0 W in Sn(BFdt 1 .OO-an. path length
and free of extraneous acidifying agents. Procedure. To determine the effect of total bromide concentration, appropriate quantities of H11rCl6, HC104, and HBr solutions were reacted together for 10 minutes in a tube placed in b o i i water. A solution of Sn(BF4)r was then added, and hating continued for exactly 2 minutes. The tube was then removed and cooled quickly to mom temperature with the help of an ice bath. The solution was then diluted to 50.0 ml. After dilution all solutions were 1.30 X 10-6M with respect to H*IrClO and 1.30 X 1O-’M with respect to Sn(BF&. The concentration of HBr was allowed to vary from 0 to 2.70M. Ionic strength and acidity were maintained constsnt at 2.70M by the addition of an appropriate quantity of HC104. To determine the effect of total tin(I1) concentration, the technique for heating and addition of reagents was the same
as above. However, SnBrz was used as the source of tin(I1) rather than Sn(BF4)n. After the h a l dilution all solutions were 1.2M with respect to acidity, bromide ion concentration, and ionic strength. The H21rCL concentration was 1.3 X 10-6M. The tin(I1) 0.80 0.70
I
L
0.00
I:’ 0
1
9
tsnl x 10’
3
4
Figure 3. Effect of tin(11) on the tiniridium-bromide system where Ir = 1.30 X 10-6M and the Br = 1.16M 1 .OO-an. path long*
concentration was varied from 5.00 X 10-3 to 5.00 x 10+M by the addition of SnBr2. DISCUSSION
Typical spectra illustrating the effect of bromide concentration are shown in Figure 1 and a plot of absorbance at 403 mp us. bromide concentration is shown in Figure 2. The spectra obtained in studying the effect of tin(I1) concentration were identical in nature with that by Pantani and Piccardi ( I ) . The absorption maximum was at 403 mp and did not change with respect to wavelength over the region of tin(I1) concentration studied. Absorbance at 403 mp us. tin(I1) concentration is shown in Figure 3.
As may be seen, the change in absorb ance per unit change in concentration of bromide and tin(II), respectively, is quite severe at lower concentrations even though both bromide and tin(I1) concentrations may be several-fold in excess of the iridium concentration. Minimal concentrations of 2.OM bromide and 0.05M tin(I1)are suggested. In the early part of this research Sn(ClO& prepared by the displace ment of Cu(C104)2with tin was used as a source of stannous ions in studying the effect of bromide concentration on the absorbance. Besides inconvenience of preparation and lack of stability of the stannous perchlorate solution, we experienced a serious explosion when the excess tin and finelydivided copper wetted with
stannous perchlorate solution dried in a filtering crucible. For this reason we sought another source of stannous ions which would also be free of a compleldng anion. Stannous fluoroborate seems ideal for this purpose. LITERATURE CITED
(1) Berman, S. S., McBryde, W. A. E., Analyst 81 566 (1956). (2) pantmi, P., Piccardi, c.,~ d chihim. . A d o 22, 233 (1960). (3) Tertiptis, G. G., Beamish, F. E., ANAL.C m . 34, 623 (1962).
EUGENE C. CERCEO J ~ m J.s MARKHAM Chemistry Department Villanova University Villanova, Pa. 19085
Device and Method for Determining Extraction pValues with Unequilibrated Solvents or Unequal Phase Volumes Malcolm C. Bowman and Morton Beroza, Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture, Tifton, Go., and Beltsville, Md.
VALUES (fractional E amount of a solute partitioning into the nonpolar phase of an equal-volume XTRACION
two-phase solvent system) have been shown to be useful in confirming the identity of gas chromatographic peaks at the nanogram level ( 1 ) and in determining the distribution properties of pesticides and other chemicals in binary solvent systems (3,4). In these determinations the phases were equilibrated prior to use to avoid the error that would result from changes in phase volumes. In determining pvalues it would be advantageous as well as timesaving to be able to employ a solution of the solute in a pure solvent and apply appropriate correction factors. p Values could then be determined by analysis of a nonpolar solution of the solute before and after extraction with several different polar solvents (each pair of solvents providing a different characteristic pvalue) without the need to equilibrate each pair of solvents in advance. At present the unequilibrated solvent is usually evaporated and the solute taken up in one of the previously equilibrated phases (not possible if solute happens to be too volatile), or the volume of the phases is adjusted after equilibration. A device described herein facilitates such analyses by providing the proper correction factors. It is convenient to use and speeds up analyses.
EXPERIMENTAL
Apparatus. The device, shown in Figure 1, was made by sealing shut a 10-ml. Mohr pipet (graduated in 0.1-ml. units) a t the point of zero volume and attaching the open end to a 10-ml. glass-stoppered Erlenmeyer flask fitted with two glass-rod legs that hold the flask upright so that the graduated tube is a t an angle of about 7 O with the horizontal. The capacity of the Erlenmeyer flask becomes somewhat larger after the flat bottom is blown out. In order to avoid leakage the g h stopper was ground to fit the flask with a glycerine slurry of 1 W m e s h carborundum dust. Procedure. The procedure is illustrated with pesticides in the hexane-acetonitrile system a t 25' C . A hexane solution of the pesticide(s) was p l d in the 5 s k of the apparatus and a 5pl. aliquot analyzed by electronm t y gas chromatography to give the analysis of the solute in the pure solvent, As. The stoppered apparatus was then clamped with the measuring tube in a vertical position or stood u p right in a test tube rack (diam. of tube is 1 cm.) so that the contents of the flask drained into the tube. After about 2 minutes the volume of the solution, V,, was read to 0.01 ml. (If a known volume of solution is added, as with a volumetric pipet, the volume need not be determined.) The second solvent (acetonitrile) was added (total volume of both solvents should not exceed 10 ml.) and the mixture equiliberated by shaking it in the flask portion and running it into the tube
and out again several times. This manipulation required about 2 minutes. The liquid in the apparatus was then allowed to drain into the tube and the volume of the nonpolar (V,) and polar (V,) phases read after about 2 minutes. A 5pl. aliquot of the hexane (upper) phase was analyzed in exactly the same manner as the first 5pl. aliquot to give the analysis of the nonpolar phase, An. Calculations. The pvalue was calculated from the following equation :
Equation 1 is the same as the one reported previously for determining pvalues with unequal phase volumes @), but is modified for use with the preaent apparatus. The component terms of E,,-i.e. analyses A,, and Asare rendered comparable by multiplying them by the volumes of the solutions analyzed ( V , and V , , respectively). The above equations may be combined to 've the following single equation whictmay be more convenient to use:
Only relative mounts of the solute need be determined since pvalues and VOL 38, NO. 10, SEPTEMBER 1966
0
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