Discrimination and Simultaneous Determination of Analogs by Derivative Spectrum Method

点击翻译按钮获取中文摘要

As the preservatives, such as methylparaben, ethylparaben, propylparaben, and butylparaben, have similar absorption spectrum which show maximum at 253-254 nm, it is not possible to discriminate them by absorption spectrum only. The addition of surfactant into their aqueous solution caused the shift of the wavelength of maximum absortion. This solubilization phenomena made it possible to measure the partition parameter of the preservative between aqueous and micellar phase. The parameter values of alkylparabens in sodium lauryl sulfate solution were in the order of butyl->propyl->ethyl->methylparaben at all temperatures where experiment were done. This means that the longer the acylchain of alkylparaben, the more can be solubilized into micellar phase. This ended up greater shift length and bigger partition parameter values. The same results were observed not in sodium lauryl sulfate solution, but also in cetyltrimethylammonium bromide solution, Tween 20 solution, and octaethyleneglycol-n-dodecylether solution. Thus the discrimination of alkylparabens were attained through the measurement of partition parameter.It was confirmed that the shift length of the mixed parabens depended on the molar ratio of its constituents. This made it possible to determine the concentration of parabens only knowing the magnitude of shift length and total absorptivity at given (maximum) wavelength. This method can be applied to any systems where absorption shift occurs as long as surfactant can cause the shift. It is a great advantage, once the calibration curve are set, then we need only the shift length and absorptivity to calculate the concentration of each components. This method can be more useful where so many samples should be handled in shorter time such as products analysis.