抄録
The antimicrobiological activity of preservatives incorporated in oil-in-water emulsion systems has been stated to be controlled by the concentration of the undissociated free species in the aqueous phase. A novel technique of ultrafiltration using the Diaflo membrane was investigated in order to measure the free methyl p-hydroxybenzoate in the aqueous phase of the oil-in-water emulsion. The method was found to differentiate between preservative that was bound, or solubilized, by the surfactant and preservative that was free in the aqueous phase. Emulsions containing various amount of methyl p-hydroxybenzoate were centrifuged and water rich layers were transferred to be ultrafiltration for the measurement of preservative concentrations. This technique could provide, in experiments of short duration, the direct estimation of the total preservative concentration in the emulsion needed to maintain a minimum inhibitory concentration of microbiologically active free preservative in the aqueous phase. Results from the ultrafiltration method were in good agreement with those from the microbiological method.
