1. Oxygen Solubility in Perfluorocarbon Emulsions
M.G. Freire1, A.M.A. Dias1, M.A.Z. Coelho2, I.M.Marrucho1, J.A.P. Coutinho1
1CICECO, Departamento de Química, Universidade de Aveiro, , Aveiro, Portugal
2Departamento de Engenharia Bioquímica, EQ / UFRJ, Bloco E, Lab.113, , Rio de Janeiro, Brasil
Introduction
Results & Discussion
Perfluorocarbons (PFCs) are highly fluorinated, inert organic compounds that can dissolve large volumes of respiratory gases. PFCs are immiscible with aqueous systems, including biological fluids, and they must be converted to an emulsified form to be safely injected into the blood vasculature as blood substitutes or to be used as oxygen vectors in biological reactors [1].  
The scope of this study is to determine the oxygen solubility in concentrated perfluorocarbon in water emulsions at 310 K (the human body temperature). To guarantee longer emulsion stability these oil-in-water emulsions were prepared in the presence of a surfactant. To study the effect of the perfluorocarbon and of the surfactant in the oxygen solubility, two perfluorocarbons were used: n-perfluorohexane and perfluorodecalin in combination with three nonionic surfactants: Lecithin, Span 20 and Pluronic F-68. The concentrations used were 50% (w/v) for the perfluorocarbons and 5% (w/v) for the surfactant. An adaptation of a precise and expedite enzymatic method for measuring the oxygen content in the oil in water emulsions was developed. The solubility of oxygen in the concentrated emulsions was correlated with each one of the pure perfluorocarbons and with the pure water and conclusions were drawn.
The composition of the emulsions studied is detailed in Table 1
Table 1. Composition of the studied emulsions
The studied emulsions were saturated with oxygen, by bubbling compressed air in it during 30 min before the analysis. The aspect of the emulsions after preparation is illustrated in Figure 2.
Analytical Method
For measuring the oxygen content in the perfluorocarbon emulsions a precise and expedite method is proposed. This method is based in the oxidation of glucose by molecular oxygen catalyzed by glucose oxidase and is commonly used for glucose determination when oxygen in excess is present. The method was adapted to measure the molecular oxygen when glucose is in excess, and can be described by the following equations:
Figure 2. Emulsions 1-6 after sonication
The oxygen content measured in the perfluorocarbon emulsions using the enzymatic method and the values expected by adding the oxygen content of pure water and PFC phases are presented in Table 2.
Table 2. Oxygen concentration per ml of the PFC emulsion, saturated with atmospheric air and the respective expected value at 310 K
aExperimental dissolved oxygen and associated standard deviation by the enzymatic method
bO2 dissolved in the pure PFC [2] + O2 dissolved in the pure water [3]
cDifference between the experimental and expected values
In order to calculate the amount of oxygen present in each emulsion, related to glucose that has been oxidized, the color intensity of the oxidized o-Dianisidine in the samples, was measured at 540 nm. In Figure 1, the intensity of the pink color against the control in the enzymatic method is presented.
If the solubility of oxygen in water and in each perfluorocarbon is considered independently the corresponding oxygen values are larger than those found with the enzymatic method and it is more pronounced in the n-perfluorohexane emulsions. This fact possibly indicates presence of a mechanism that hinders the dissolution of the oxygen in the emulsion.
The solubility of water in the used PFCs was measured in our laboratory with a Karl Fischer titrator, Metrohm, model 737 KF Coulometer, at K, obtaining (1.46±0.04).10-3 mol.L-1 for water in n-perfluorohexane and (1.30±0.09).10-3 mol.L-1 for water in perfluorodecalin. Water solubility in PFCs is in the same order of magnitude of the solubility of oxygen in the studied emulsions.
The small extent of the solubilization of PFCs in water cannot be considered as one of the mechanisms that obstruct the solubility of oxygen in the aqueous phase of the emulsion. On the other hand, the solubility of water in pure liquid PFCs occurs in great extent and must be considered as a possible interference that decreases the solubility of oxygen in the emulsions.
Figure 1. Intensity of the pink color against the control in the enzymatic method
References & Acknowledgments
[1] Riess JG, “Fluorocarbon based Oxygen Delivery, Basic Principles and Product Development”, in Blood Susbstitutes: Principles, Products and Clinical Trials, Vol II, Ed. Karger landes Systems, Switzerland, 1998
[2] Dias AMA, Freire MG, Coutinho JAP, Marrucho IM, Fluid Phase Equilibria (in press)
[3] DIPPR, Thermophysical Properties Database, 1998
The authors thank financial support from Fundação para a Ciência e a Tecnologia, Portugal (POCTI/EQU/44427/2002)
and from FAPERJ and CNPq, Brasil
M. G. Freire acknowledges the scholarship SFRH / BD / / 2003