Experiment: The LAB tests different forms of vitamin C
We aim to create high-quality products, so we pay close attention to the selection of cosmetic ingredients. We do not hide the fact that we often conduct additional ingredient tests on our initiative, and in this way, we learn more about the ingredient than what the raw material manufacturer specifies. Driven by youthful curiosity, we tested vitamin C and its different derivatives: sodium ascorbyl phosphate, 3-O-ethyl ascorbic acid (hereinafter: ethyl ascorbic acid), and ascorbyl glucoside in our laboratory.
So, first, we prepared aqueous solutions of all four test ingredients, in which the concentration of the ingredients was standardized - both vitamin C or its derivatives and preservatives. We emphasize that cosmetic ingredient manufacturers often specify procedures that are necessary to stabilize active substances. Our ingredients did not require a stabilization procedure, but we took into account all other requirements of raw material manufacturers. After preparing the samples, we kept them in an incubator at 45 degrees Celsius for 30 days (otherwise known as an accelerated stability test), and we kept one sample of each ingredient at room temperature (control sample).
We determined the concentration of vitamin C and its derivatives by two methods - spectrophotometry and titration. One of the parameters we monitored was also the pH value.
In the cosmetics industry, the product's pH value is one of the most important indicators that must be determined. It is probably known to everyone that different pH value products are recommended for different skin types: products with lower pH values are recommended for oily skin types, while products with higher pH values are recommended for mixed and dry skin types. For this reason, the pH value is determined for each cosmetic product, and it is essential that the product formulation is stable and its pH value does not change over time.
During this experiment, we determined the pH value of each sample before and after an accelerated stability test. The study aimed to determine if different forms of vitamin C are stable and do not change the pH value, which would suggest that changes in the pH value of the active substance would affect the pH value of the final, composite (containing more components) product. During spectrophotometric analysis, we recorded the absorption spectra of each sample, including control samples. Since the literature analysis did not provide all the absorption coefficients of vitamin C and its derivatives, which are necessary for calculating the concentration of these ingredients from spectrophotometric results, we compared the maximum absorption changes of all samples. For this reason, we conducted additional experiments in which we determined the concentration of vitamin C or its derivatives by titration. We compared the results obtained by both spectrophotometric and titration methods to evaluate the reliability of the results.
First, let's discuss the sample in which L-ascorbic acid was used as the active substance. After the accelerated stability test, we see that the pH value of this sample did not change, but the concentration of vitamin C decreased by 9.7% and 12% according to the titration and spectrophotometric methods, respectively. In the case of sodium ascorbyl phosphate, the pH value decreased by 0.67 units, while the concentration decreased by 2.7% and 2% according to the titration and spectrophotometric methods, respectively. In the case of ascorbyl glucoside, the pH value increased slightly by 0.17 pH units, while the concentration decreased by 20% according to the spectrophotometric method. In the case of ethyl ascorbic acid, we observed the highest stability of the vitamin C derivative compared to other derivatives used during the study.
When creating various cosmetic products, heat and the pH of the environment inevitably affect vitamin C or its derivatives, and later, when the product is stored or used, light and oxygen can change the properties of the active ingredient used in the product or reduce its effectiveness by damaging the compound structure. The main possible side effect and changes in the product mass occur due to the oxidation of vitamin C or its derivative. During oxidation, inactive substances are formed, which do not have the desired effect and sometimes irreversibly change the properties of the final product, such as color, pH, and product mass consistency. Therefore, these results clearly demonstrate that when creating a cosmetic product formula, each ingredient must be carefully selected, and when selecting a cosmetic product from a store shelf, consideration should be given to the form of each ingredient, which can be seen in the product's INCI list!
-- The LAB