Ib capillary
I
la
h
l\f
100
40
60
80
20
0
20
40
HZ
Figure 1. ( a ) Comparison of effects of DPPH on HA-100 and HR-220 spectra of TMS in CHC13relative to corresponding spectra of undoped solution contained in a capillary. Temperature: 33 OC. (b) Comparison of HA-100 and HR-220 spectra of TMS in CHCI, relative to neat TMS sealed in a capillary Note Added in Proof. Subsequent to the submission of this communication, Becconsall et a[. [J. K. Becconsall, G. D. Davies, and W. R. Anderson, Jr., J. Amer. Chem. SOC.,92, 430 (1970)l have presented, without explicit experimental proof, equations equivalent to Equations 1’ and 4‘ in this paper. ACKNOWLEDGMENT
One of us (DHL) acknowledges several discussions with R. C. Rosenberg of this laboratory, who has independently
noted the discrepancy between A-60 and HR-220 results of a factor of 2 in the paramagnetic susceptibilities determined using Evan’s method (Reference 4) and when Evan’s formula was used to interpret the bulk susceptibility shifts. RECEIVED for review January 2, 1970. Accepted March 16, 1970. Research supported in part by USPHS Grant No. G M 14523-03 from the Division of General Medical Sciences and Grant No. GP-8540 from the National Science Foundation.
Polystyrene Sulfonates as Stable Polarographic Maxima Suppressors in the Determination of Periodate and Cobalt(l1) R. D. Corlett, W. G . Breck, and G. W. Hay Queen’s University, Kingston, Ontario, Canada POLAROGRAPHIC MEASUREMENT of excess periodate in a kinetic study of the oxidation of certain carbohydrates was hampered by the unwanted oxidation of the conventionally used maxima suppressors (e.g.,Triton X-100, gelatin) or by wave-splitting of the two-electron process, IO4- 2H 2e +.1 0 3 HzO or by severe reduction of the maximum diffusion current (id)at low concentrations. As part of a program to develop an
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ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, J U N E 1970
automated polarographic analysis, it became necessary to find a suppressor which was stable to periodate ion over an extended period of time, and which did not reduce the id value appreciably. The completely sulfonated polystyrene sulfonic acids (provided as the sodium salt) of narrow molecular weight ranges recently developed by The Dow Chemical Company (Available from Technical Service and Development 2020 Building, Abbott Road Centre, Midland, Mich. 48640) were
Table I.
Maximum Suppression Points (M,) Expressed as 10-4 % of Suppressor Ion NC SA Supporting electrolyte studied 1557 NC 1585 1291-1 0.8 1.6 0.8 020 . 2 M HOAc :O. 1M LiOAc 1.0 1.o 0.8 IO3-, 0 . 2 M HOAc :O. 1M LiOAc 1 .o 0.8 0.2M H0Ac:O. 1M LiOAc IO4- 1 . 0 12.0 2.0 0.2MHOAc:O.lMLiOAc Pb2+ 0.6 20.0 Co2+ 4.0 Not 0.5MPyridine:l.OMKCl effective
found to be particularly useful for the purpose owing to their structure,
100
-M 0
E80
’
d
2ol&s&ErL 5
10
15
20
25
30
35
Time in ceH minutes Figure 1. Decomposition rate for periodate in cell. Originally 0.5 pmoles/2.5 ml ; 0.05 pmoles/2.5 m l o
Thus these solutes were found to eliminate maxima, increase viscosity, cause no foaming, and can be adsorbed at the surface of the drop without forming a nonionic (and hence nonconducting) bridge between the surface and the solution. The effects of polymers of three different molecular weight ranges on various polarographic waves are to be described. EXPERIMENTAL
The three polymers used were: Dow N C 1557, mol wt 40,000; N C 1585, mol wt 500,000; and SA 1291-1, mol wt 2-4,000,000. Each was dissolved in water in an amount to make a 0.05 (w/v) solution, subsequently diluted to 0.005 %. Maximum suppression points (M,) were obtained by plotting i, - id (where i, is the value of the current at the maximum peak) against concentration of suppressor (as %), following the method of Heyrovsky and Zuman ( I ) , and are given for several ions in Table I. For example, a volume of 2.5 ml of a buffer solution, 0.2M HOAc:O.lM LiOAc, was introduced into a 5-ml cell, temperature controlled, and stirred in contact with air. The oxygen waves were measured with a Metrohm Polarecord using a dropping mercury cathode and both mercurous sulfate and mercurous acetate reference electrodes. Then 0.01-ml increments of suppressor solution (0.005 %) were made, stirred in, and the oxygen wave was recorded in each case. Values of i, - id and id of the plateau beyond the maximum were plotted, respectively, against the concentration of suppressor. These showed a rapid diminution of maxima with suppressor added and a relatively small reduction in values of id beyond the suppression point for a fivefold increase in suppressor concentration. To ascertain that the suppressors were inert to periodate over an extended period, solutions were prepared all with the same periodate content, some blank and the others made up to give concentrations of the various suppressors 0.008 (1) J. Heyrovsky and P. Zuman, “Practical Polarography,” p 162,
Academic Press, London, 1968.
(corresponding to 100 X Me). At 24-hour intervals, 2.5-ml aliquots were analyzed, as also were 2.0-ml aliquots of the blanks to which were added aliquots of the various suppressor solutions to equal the other corresponding concentrations, No increase in decomposition of periodate over the blanks was observed. Further, to each of a set of solutions of different periodate concentrations, a volume of suppressor solution corresponding to 10 X M , was added to determine the id of the periodate wave as a function of concentration, The relation between wave height and concentration was linear, indicating no appreciable reaction between the periodate and suppressor. One of the difficulties encountered in the polarography of periodate is its decomposition in the cell (which can be associated with the oxidation of mercury salts). The polystyrene sulfonates do not eliminate this problem (see Figure l), but do permit the prior mixing of suppressor and reaction solution, the preparation of solutions in the reaction vessel, and, on anaerobic transfer of aliquots, the immediate analysis of the sample, thus minimizing the effect of any decomposition. Possibly these polystyrene sulfonates or similar substances may prove to be suitable in cases where conventional suppressors have been ineffective. For example Lingane and Kerlinger (2) observed that the Co(I1) maximum was difficult to suppress with gelatin; in 0.5Mpyridine: 1.OMKCI we have found complete suppression using the sulfonate polymers N C 1557 and SA 1291-1, but not N C 1585. Furthermore, the Pb(I1) maximum was suppressed by all three polymers, and there was no evidence of any precipitation of lead by sulfonate ion. The polymers can suppress both positive and negative maxima.
RECEIVED for review February 11, 1970. Accepted March 27, 1970. Work supported in part by a grant from the National Research Council of Canada. (2) J. J. Lingane and H. Kerlinger, IND.ENG.CHEM., ANAL.ED. 13,77 (1941).
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