The effect of uncharged, dipolar phloretin on anion and cation conductance through a black lipid membrane can be used to study its adsorption behavior. The adsorption of phloretin can be described by a Langmuir isotherm with weak dipole-dipole interaction.

the base line is considerably improved, and finally a differential pulse voltammogram synchronized to a DME in which the dc contribution is not important.Charging Current Due to Pulse Application. The current required to charge the double layer after the sudden rise in potential caused by the application of the pulse is given by ( 3 ) :where R is the cell resistance, C is the double layer capacitance, and t is the time after the pulse was applied. This current decays rapidly to zero, so that if the pulse period is sufficiently long, this component will be negligible. If we assume C = 4 MF, R = 1 K, AE = 25 mV, and t = 40 msec, then ic,pulse = 1 PA. Under normal conditions, the double layer capacitance current arising from the pulse application can be ignored.The need for sufficiently long pulses to minimize ic,pulse limits the scan rates used in this technique. A reasonable compromise between fast scan rates and sufficient points on the potential-current curve enabled us to use potential scan rates of up to 200 mVlsec. CONCLUSIONSFast sweep differential pulse voltammetry at a DME has much to recommend itself as an analytical technique by being able to combine the dual advantages of speed (

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2367higher detection limit, is probably due to surfactants still present in solution after cleanup. If lower limits are desired for a particular application the extended cleanup procedure can be used with the TEA via direct injection. The additional steps do not provide sufficient cleanup to increase detection limits via the D P P method.Thus an analyst has available a choice of methods depending on levels. In either case preparation times are short;for whole blood an average time is approximately 10 min. Challis, B. C.; Osborne, M. R. IARC Scl. Pub/. 1975, (7) Magee, P. N.; Montesano, R.; Preussmann, R. In "Chemical Carcinogens"; Searle, C. E., Ed.; American Chemical Society: Washington, DC, 1976; ACS Monograph Series, No. 173, Chapter 11. (8) Fan, T. Y.; Krull, I. S.; Ross, R. D.; Wolf, M. H.; Fine, D. H. IARC Scl. NO. 9 , 94-100. (1) Howard, J. W.; Fai!io, T.; Watts, J. 0. J. Assoc. Off. And. Chem. (2) Hotchkiss, J. H.; Libbey, L. M.; Scanlan, R. A.

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