RESULTS A N D D I S C U S S I O N
The data in Table I show the results obtained, and the rate plot obtained for the mixture of potas#jium bromate and sium dichromate is shown in Figure ince chlorate does not react with iodide, it does not, interfere in the differential analysis of the iodate and bromate contents of ternary mixtures of these compounds. Determining the total halogen content of such mixtures and obtaining the chlorate by difference tem of analysis for all three components. The purpose of this communication is to demonstrate the applicability of flow methods to the analysis of mixtures. I t should be pointed out that measurement techniques other than those used here most probably ‘can be applied to differential kinetic a.nalysis using flow systems. Blaedel and Olson ( 2 ) recently described an amperometric meassurement technique in a flowing system which they applied t o the analysis of glucose based on an enzymatic oxidation reaction. These workers measured the amount of reaction occurring between two tubular platinum electrodes in the flowing stream and, by comparison with the amount of reaction in solutions of known concentration, determined t’he concentration of glucose in unknown samples. Other techniques which have been applied to measure reaction velocities are conductance and electro-
Table I.
A Potassium iodate Potassium iodate Potassium periodate Potassium dichromate
~-
Analytical Results for Mixtures
5 Faster Reacting
Mixture R Potassium bromate Potassium bromate Pot assiuni bromate Potassium bromate
Component, A Found Present 24 3 24 8 56 8,57 3 56 2 13 8 14 2
C
Potassium chlorate
motive force measurements ( 1 1 ) , temperature rise in exothermic reactions ( I , 8, 9 ) , polarographic measurements (3, 4),and si)ectrophotometri(, measurements (5, I S ) . Most of these techniques are 1-ery rapid since the measurements can be made a t many points along the observation tube and therefore require only one run. They do require specialized instrumental arrangements.
9 5
9 6
29.2
30.6
( 7 ) Hartridge, H., Roughton, F. J. W., Proc. Roy. Soc. A104, 376 (1923). ( 8 ) La Mer, V. K., Read, C. L., J . A V I . Chem. Soc. 52, 3098 (1930). ( 9 ) Pinsent, B. R. R.,Pearson, L., Roughton, F. J. W.,Truns. Faraday soc. 52, 1512, 1594 (1956). (10) Roughton, F. J. W.,Chance, B., “Techniques of Organic Chewistry,” Vol. VIII, 2nd ed., Chap. XIV, S. L. Fries, E. S. Lewis, A . \Veissberger, eds.. Interscience. Sew York. 1963. (11) Saal, R. ?;. J.)’Rec. ‘I’rav. C‘hzm. 47, 7 3 . 264 (1928). - -, (12) ’Siggia, S., Hanna, J. G., Serencha, ?;. AI., h . 4 L . C H E M . 35, 575 (1963). (13) Theorell, H., Chance, B., Acta Chem. Scand. 5, 112i (1951). \
LITERATURE CITED
(1) Baternan, J. B., Roughton, F. J. IT,, Biochem. J . 29, 2622, 2630 (1955). ( 2 ) Blaedel, W. J., Olson, C., ANAL. CHEM.36, 343 (1964). (3) Bonnichsen, R., Chance, B., Theorell, H.. Acta Chem. Scand. 1. 685 (19471. ( 4) Chance, B., Bwchem: J . ‘46, ’387 (1950). ( 5) Chance, B., Seilands, J. B., J . B i d . Chern. 199, 383 (1952). (6) Haggett, 11. L., Jones, P., Oldharn, K. B., J . Chern. Educ. 40, 367 (1963).
J. GORDON Hama SIDNEY SIGGIA Olin Research Center Olin Mathieson Chemical Corp. 275 Winchester Ave. Sew Haven 4,Conn. RECEIVEDfor review April 13, 1964. Accepted June 24, 1964.
Electroc hemicaI Studies Using Cond ucti ng Glass Indicator Electrodes SIR: The n-type, broad band (6) semiconductor property of tin oxide has been utilized for seveiral years to make semiconduct,ing glass surfaces. These tin oxide-coated glasses have been used for a potentiometric electrode by Cooper ( 3 ) and for p1ai;ing and deplating of ailver on glass by X t n t e l l and Zaromb (?). 1Te wish to report the use of such a conducting glass electrode (CGE) as a working indicator electrode for the oxidation and reduction of inorganic ions as lvell as organic molecules in both acidic and basic solutions. The advantage of C G E is i,ts optical t,ransparency in the 3050- to 7000-A. r of the spectrum which makes po the spectral monitoring of certain absorbing electroactivr species, intermediates, or products concurrently during an electrolysis. The application of C G E to the spectral monitoring of an electrode process is herein demonstrated.
EXPERIMENTAL
Apparatus. Tin oxide-coated glass surfaces were obtained commercially from Libbey Owens Ford Glass Co. Pret,reatment prior to use consisted of washing t h e surface with reagent grade benzene to remove adherent organic adhesive materials followed by light rubbing of the surface with wetted, 1000-mesh silicon carbide powder, and t,lien thoroughly washing with distilled water. S o special precautions or pretreatments were necessary hetween runs either in acidic or alkaline medium. When not in use, t.he electrodes were stored d r For chrono1)otentiometry ammetry studies. cells were constructed with the conducting mrface in a narrow ring configuration to maximize the ratio of surface area to surface resistance. For spectral studies during electrolysis, cells were made from cither one or two flat Illates of conducting glass. Further details of cell construction and con-
figuration will be discusse in a future paper. The circuits for the construction of triangular wave generator and potentiostat were identical to those described by .Ilden, Chambers, and .‘idams ( 2 ) . The chronopotentiometric circuit and equipment were conventional in all respects. An Electro-Instruments Model lOOT13 X-I.’ recorder and Leeds 8: Sorthrup Model H strip chart recorder were wed. XI1 potentials are reported with respect to a saturated calomel reference electrode (S.C.E.) Reagents. Xnthraquinone was purified according to published procedure ( 5 ) . Eastman Iiodak TThite Label Grade o-tolidine was used without further purification. Standard ferrous ammonium wlfate (99.85Oj,) obtained from Thorn Smith Co., Royal Oak, lIich., was used for the source of ferrous ion. All other chemicals were of reagent, grade. Distilled water was redistilled from alkaline permanganate solution. V O L . 36, NO. 10, SEPTEMBER 1964
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1
I
2
2.0
1.5
I 1.0
I
I
05
080
I
I
-0.5
-1.0
J
RESULTS A N D DISCUSSION
A typical resistance value of 60 ohms
Traces il and B in Figure 1 show the background scans of C G E in degassed solutions of 1F H2SOaand IF Na2C03, respectively. The usable potential limits of C G E were slightly greater than those attained a t a platinum electrode in the same media. Trace C in the same figure shoas a current-voltage (CV) curve for a cyclic scan of 1.25 X 10-3F ferrocyanide in 0.1F KC1 solution. Because CGE possesses an inherent surface resistance, the peaks of the CV curves were depressed ab a consequence of the nonlinearity of potential as a function of time a t the electrode surface during the scan. Of the variety of methods available for measuring resistance, a simple and satisfactory procedure adopted in the present case was to plot the half-peak potential, E , as a function of the halfpeak current for varying concentrations of ferrocyanide. The plot was linear, and assuming a reversible redox reaction, the resistance was the slope of the line.
was obtained for one of the voltammetric cells. Correction to the peak current, I,, which deviated because of the nonlinearity of scan, was accomplished by application of a method similar to that used by Delahay and Stiehl ( 4 ) . For scan rates below 4 volt-minute-', the plot of corrected I , us. concentration was linear and extrapolated to the origin. The proportionality of corrected I , with square root of scan rate established the dependence of I , on mass transfer by diffusion. Since correction of resistance polarization is much simpler when a constant current mode is employed, chronopotentiometry was extensively used for evaluation of CGE. Table I summarizes chronopotentiometric data for some electro-oxidations and reductions. The corrected values for the reduction of ferricyanide and anthraquinone, and the oxidation of ferrous ion are in good agreement with those ob-
Chronopotentiometric Data Obtained Using CGE
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ANALYTICAL CHEMISTRY
Eiir
I
I
Traces A to D taken with constant currents of 297, 203, 105, a n d 60 pa., respectively
scan rote, 4 volt-minute-'
iT1l2/C Compound or ion (pa.-eecond1jamole-1 liter) Fe(1I) in 0.1F HzSO~ 0.736 f 0,010 Ferricyanide in 0.16F 0.745 f 0.007 KC1 Anthraquinone-l,5-~ul1.445 f 0.029 fonic acid ( N a salt) 0.1F NaZCOa o-Tolidine in 1F HC1 1.030 f 0.044
1
Figure 2. Spectral monitoring at 4370-A. wavelength during electro-oxidation of o-tolidine at CGE
-15
Figure 1. Traces A and B are background cyclic scans of CGE in 1 F H2S04'and 1 F Na2C03, respectively. Trace C is scan in 1.25 X 1 0-3F ferricyanide in 0.1 F KCI solution
Table I.
I
TIME, SEC.
E v s S.C.E.
Geometric a r e a of electrode, ca. 2 sq. cm.;
I
US.
S.C.E.
0 . 8 2 f 0.02 (corr.)
0.203 =k 0.004 (corr.) - 0 . 8 2 f 0.01 (corr.)
1.00 f 0 . 0 2 (uncorr.)
tained a t other electrodes ( I , 6). The constancy of Z'T112/Cis certainly within expected limits for a purely diffusioncontrolled electrode process at a planar electrode. Adsorption effects, if any, were not observed for the ions studied. Spectral background of C G E possessed interference fringe patterns with amplitude of ea. 0.05 absorbance units. Interference probably arises from internal reflectance between the ti0 oxide and glass surfaces. Correction to a spectrum for this background was simply made. However, reproducible placement of cell in light path of spectrometer was necessary. Curves A to D in Figure 2 are recordings of spectral absorbance us. time for the chronopotentiometric oxidation of otolidine a t CGE. The concentration of the product of the o-tolidine oxidation is being followed by monitoring at a wavelength of 4370 A. The spectral absorbance is related to the product concentration by the usual Beer's law. The concentration during electrolysis is given by C = it/nFV, where i iq the current in amperes, t is time of electrolysis in seconds, V is volume in liters, and n and F have their usual significance. If n, F , and V are constants, C is proportional to either absorbance or time for a constant current process if there are no complications to the electrode process. Beyond the chronopotentiometric transition time, T , the rate of o-tolidine oxidation is now governed by the rate of diffusion for the condition where the concentration of o-tolidine is zero a t the surface. The usual relationship for linear diffusion a t planar electrodes for such a condition applies, and the portion of the current consumed by o-tolidine is proportional to the square root of time.
'The absorbance of curves to D is initially linear with time and t,hen follows a square root dependence of time, excel)t a t longer times when convection contributes significantly to mass transfer. The transition time may be determined from the linear portion of the absorbancy curves. The ease with wh,ich spectral studies can be made using C'GE should aid the elucidation of mechanism and kinetics of wrtain electrode processes, in particular those cases where a chemical reaction may follow the charge transfer step. Other applications of CGE, such
as cells for electron spin resonance work or process stream analyzers may prove advantageouq. The scope and limitations of C G E are under further investigation and will be reported in the near future.
(4) Delahay, P., Stiehl, G. L., J . Phys. Chem. 55, 570 (1951). (5) Kuwana, T., ANAL.CHEM.35, 1398 (1963). (6) Loch, L. ll.,, J . Electrochem. SOC.110, 1081 (1963). (7) Mantell, J., Zaromb, S., Zbid., 109, 992 (1962).
LITERATURE CITED
THEODORE KCWANA R . KEITHDARLINGTON DONALD W. LEEDY
(1) Adams, R. X., in,,"Treatise on An-
algtical Chemistry, I. M. Kolthoff and P. J. Elving, eds. Part 1, Vol. 4, Chap. 47, Interscience, Kew York,
1963. ( 2 ) Alden, J. R., Chambers, J. Q., Adams, It. N., J . Electroanal. Chenz. 5, 152 (1963). (3) Cooper, W., .Vatwe 194, 560 (1962).
Department of Chemistry Cniversity of California Riverside, Calif. RECEIVEDfor review May 25, 1964. Accepted June 26, 1964.
Gas Chr(3 ma tog ra phic Determina ti o n of Isomers of Phenylenediamine SIR. A recently reported method for the quantitative de1,ermination of the isomers of phenylenediamine depends upon measurement by an electrometric (polarographic) method ( 2 ) . To date the most satisfactorj, qualitative determination is based upon reduction of phoiphomolybdic acid ( I ) . A rapid gas chromatographic method is presented here which permits accurate qualitative
and quantitative determination of mixtures of o-, m- and p-phenylenediamines. EXPERIMENTAL
Apparatus. The i m t r u m e n t used to obtain the chromatograms was a Model 500 linear programmed temperature gas chromatograph (F Bi h3 Scientific Corp.) equipped with a 1mv. Drown Electronik Recorder (JIinneapolis-Honeywell Co.) wit,h a chart speed of 15 inches per hour. Operating Conditions. Detector cell temperature, 310" C.; detector cell current,, 180 ma.; injection port temperature, 320" C. ; helium flow a t exit, 125 ml. per minute; starting column temperature, 150" C . ; final column temperature, 250" C . ; programmed temperature rate, 5.6" C. per minute. Column Preparation. A 2-foot length of 1/4-inch 0.d. stainless steel tubing was packed with 25% by weight Triton X-305 on 60- to SO-mesh Chromosorb W. Reagents. The isomeric phenyle n d i a m i n e s were purified by distillation in a nitrogen atmosphere. T h e known mistures were prepared and diluted just prior to analysis to minimize errors due t o air osidation.
Table I.
--
w
v)
z
X
00
0
w
a
l-
a
0
a
0
3 Y u a
4
I
.
.
.
.
.
0
2
4
6
(1
. 10
12
14
I6
18
-r
20
T I M E , HIHUTES
Figure 2. Chromatogram from analysis of p-phenylenediamine containing 1 .Oyoortho isomer
Analysis of Synthetic Mixtures
Deviation, Mixture I
T I M E , MlhIUTES
Figure 1 . Chromatogram from analysis of mixture of equal amounts of 0 - , m-, p-phenylenedisamine
II I11
added 33.3% o-Phenylenediamine 33 3% p-Phenylenediamine 33 3(,4 ?,1-Phenyleriediamine 10,05&o-Phenylenediamine OO.O(,", p-Phen.leiiediaiiiiiie 1.Oyoo-Phen\lenedinrnine 9 0 . 0 % p-Phen:vleiiediariiine
Found 34.253 o-Phenylenediamine 32 45i p-Phenylenedianline 3 3 . 3Yc m-PhenI.lenedianiine 0 . 5 5 o-Phenylenediariiine 00 5f,1 p-Phenylenediaflliiie O 87; o-Phenylenediarnine 09.27; p-Phenylenetliamine
VOL. 36, NO. 10, SEPTEMBER 1964
CY /C
+O. 9 - 0 $1 0.0 -0.5 10.5 -0 2 +O. 2
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