Studies on n-octanol/water partition ratio of electroactive species using microelectrode voltammetry

• Grant number: 13/24647-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2014
• End date: July 31, 2014
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Analytical Chemistry
• Principal Investigator: Tiago Luiz Ferreira
• Grantee: Gabriel Guerra Faura
• Host Institution: Instituto de Ciências Ambientais, Químicas e Farmacêuticas (ICAQF). Universidade Federal de São Paulo (UNIFESP). Campus Diadema. Diadema , SP, Brazil

Abstract

The present project aims to use microlectrode voltammetry for the n-octanol/water determination of partition (logP) and distribuition ratios (logD) of electroative species as hydroquinone, ascorbic acid and acetaminophen. Generally, the experimental determination of partition and distribuition ratios is carried out by shake-flask method, and the most common method of measuring the equilibrium concentration of the solute on both phases is UV/vis spectroscopy. However, the determination of logP or log D using this technique can lead to unreproducible results due to: (I) the adsorption of the solute on the walls of the tubes and cuvettes; (II) aggregation factors that depends on the concentration of solute; (III) determination of logP of uncolored solutes, (IV) solutes that increase the miscibility between the solvents, altering the refractive index of both phases; amongst others. Thus, the development of an alternative method for the partition or distribution ratio determination is desirable. The use of voltammetry with microelectrodes has some advantageous features compared to that carried out with conventional electrodes as high faradaic current / capacitive current ratio and high efficiency in mass transport. Regarding the determination of the partition ratio, the main advantage is the possibility of performing voltammograms in media with low electrical conductivity due to the low intensity of current supplied by the microelectrodes, i.e. there is no need to add electrolyte to the aqueous solution for measurements. The main aim of this project is to estimate the absorption of these species by skin and other biological membranes from the obtained values of logP and logD.