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
1427
Figure 1.
Apparatus for p-value determination
En values are ratios. With a linear
response to the solute, the only gas chromato aphic datum needed is the ratio of t f e response in the two analyses (&/AI), which we may designate as R, Incorporating this value in Equation 2 we get: = V.
-
RaVp R.(V.
W
60-
u)
z
0
a
-
v)
- V,)
(3)
boo
# 0
RESULTS AND DISCUSSION
The data for six trials with seven pesticides in unequilibrated phases of Mering volume ratios are given in Table I. The pvalues in these trials, given in the last column on the right, agreed with those shown in parentheses, which were determined with equal volumes of equilibrated solvents. High, intermediate, and low pvalues are represented. The hexane-acetonitrile system was selected because, on mixing, equal volumes of these solvents produce
0
L 200-
I P
I
8
4 MINUTES
0
I
Figure 2. Chromatograms of 4 pesticides in hexane Before (solid line) and after (dotted line) extrac-
tion with acetonitrile (a I= 0.5)
Table 1. Determination of p-Values of Pesticides at 25' C. With unequilibrated solvents (hexane and acetonitrile) and solvent phases of different volume ratios in the apparatus of Figure 1 Solvent Nonpolar Polar Ratio of phsse analyses, Trid Vp,d. Pesticide A./A.or R. pVdue" 1 3.05 2.25 6.92 Lindane 0.061 0.13 (0.12) Heptachlor 0.381 0.55 (0.55) Dieldrin 0.194 0.34 (0.33)
t:%, $kss2i.
2
3
4
4.95
7.30
3.40
4.46
7.21
2.56
4.84
1.76
6.99
m$ET Heptachlor
Diefdrin ,p -DDT %ndane Heptachlor Dieldrin Vd'-pT
0.212 0.127 0.589 0.345 0.402 0.361 0.838 0.678 0.730
0.36 (0.37) 0.12 (0.12) 0.55 (0.55) 0.33 (0.33) 0.38 (0.37) 0.12 (0.12) 0.54 (0.55) 0.33 (0.33) 0.39 (0.37) 0.73 (0.72) 0.40 (0.39) 0.17 (0.17) 0.72 (0.72) 0.39 (0.39) 0.18 (0.17) 0.74 (0.72) 0.38 (0.39) 0.17 (0.17)
0.666 +2hlordane 0.259 TDE 0.095 5 5.05 4.65 4.49 Aldrin 0.792 ychlordane 0.429 TDE 0.201 6 7.42 7.29 1.91 Aldrin 0.933 ychlordane 0.715 TDE 0.442 ' pvalues determined experimen+ly from equal volumes of equilibrated solvents are given in parenthesee for cornpanson.
1428
ANALYTKAL
CHEMISTRY
unequal phase v6lumes (43% upper, 57% lower). The system is also very widely used in pesticide analysis and the solvents are readily available in pure form. Figure 2 shows a typical set of chromatograms in which the pvalues of four pesticides were determined by analyses before and after extraction. The results of Table I are satisfactory only because the apparatus makes it possible to measure the liquid volumes accurately (to 0.01 ml.). A small amount of liquid adheres to the inner wall of the flask during the measuring process. If about 2 minutes is allowed before the phase volumes are read, drainage appem to be sufliciently complete to make the potential error negligible. The use of very small volumes may lead to error owing to inability to determine their volumes with sufficient accuracy. In previous reports (1-4) the p value was defined as the fractional amount of solute partitioning into the upper phase of an equal-volume twophase system. We have since found it advantageous to redefine the value in terms of the nonpolar phase, as this makes possible a more meaningful comparison of pvalues obtained from different solvent systems, including those in which the nonpolar phase is the lower one. For advantages, experimental details, precautions, and background on the use of extraction pvalues, previous publications (1-4) should be consulted. LITERATURE CITED
(1) Beroza, M., Bowman, M. C., ANAL. CHEM.37,291 (1965). (2) zbid., 38, 837 (1966). (3) Berora M., Bowman, M. C., J . Assoc. bfi. Agr. Chemists 48, 358 (1965). (4) Bowman, M. C., Beroza, M., Zbid., p. 943.
F'IUJSENTEDat the joint meetin of the W(tshinpn and M land ACS hetione, Umversity of Mq%d, College Park, Md., May 6, 1968.
