Chemically stable ester derivatives of vitamins A, C and E have become a focus\r\nof interest for their role in the satisfactory results in skin aging treatments. Accordingly,\r\nthe aim of this study was to evaluate the physical and chemical stability of a cosmetic\r\nformulation containing 1% retinyl palmitate, ascorbyl tetraisopalmitate and tocopheryl\r\nacetate, alone or in combination. In the studies of physical stability, a Brookfield rheometer\r\nwas used to determine rheological behavior of formulations containing the vitamins.\r\nChemical stability was determined by HPLC on a Shimadzu system with UV detection.\r\nResults showed that formulations had pseudoplastic behavior and that vitamins did not\r\nalter their apparent viscosity and thixotropy. In the chemical stability studies,\r\nfirst-order reaction equations were used for determinations of the shelf-life of vitamins\r\nderivatives considering a remaining concentration of 85%. Combined vitamins in a single\r\nformulation had a slightly lower degradation rate as compared to different preparations\r\ncontaining only one of the vitamins. Considering that many cosmetic formulations contain\r\nvitamin combinations it is suggested that the present study may contribute to the\r\ndevelopment of more stable formulations containing liposoluble vitamins.
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