A VALIDATED OMC ANALYSIS: SPECTROPHOTOMETRIC METHOD 169 transferred into another volumetric fl ask (50 ml), and diluted into 5 μg/ml with the dif- ferent solvents. An absorbance pattern of each solution was recorded during 200–400 nm. The best solvent affording maximized absorption without the presence of interference effects was obtained. The stock OMC solution (0.8 mg/ml) was prepared into serial dilu- tions (4, 8, and 12 μg/ml), which were further validated on linearity, range, accuracy, and precision of the analysis. Linearity, range, accuracy, and precision. The above mentioned validated parameters were assessed at fi ve different concentrations (4, 6, 8, 10, and 12 μg/ml), and the absorbance was recorded at 310 nm. The linearity was determined with a determination correlation (r) of more than 0.995, in addition to a recovery (%) calculation as well as a relative stan- dard deviation (%RSD). All of the experiments were performed six times. VALIDATION OF OMC SUNSCREEN ANALYSIS METHOD Specifi city. The cosmetic bases (8 g) were weighted into volumetric fl asks (100 ml), sepa- rately, prior to the addition of methanol to achieve the fi nal volume. The solution was fi ltrated through Whatman no. 5 fi lter paper. The fi ltered solution (5 ml) was pipetted into 50 ml volumetric fl ask and diluted into 5 μg/ml. The absorbance was determined as described in the specifi city of OMC analysis. Accuracy and precision. The cosmetic bases (8 g of 1% OMC, 2 g of 4% OMC, and 1.07 g of 7.5% OMC) were weighted into six volumetric fl asks (100 ml). The stock OMC solution (0.8 mg/ml, 10 ml) in each fl ask was adjusted to 100 ml with methanol and mixed thor- oughly. The solution was fi ltered and diluted into 5 μg/ml. The absorbance determination was done at 310 nm as mentioned earlier. The procedure was conducted in six replicates. Repeatability of the method. OMC sunscreens in O/W and W/O emulsions, and mineral oil at different concentrations were weighted differently into the 100 ml volumetric fl ask Table I Ingredients of O/W and W/O Emulsions Emulsion Ingredient % (w/w) O/W Isopropyl myristate 12.0 Isopropanol 3.0 OMC 1.0 or 4.0 or 7.5 Stearic acid 1.0 Cetyl alcohol 0.5 Triethanolamine 1.0 Carbopol 934 0.2 Deionized water qts. to 100 W/O Petrolatum 17.0 Emulsifying wax 4.0 Calcium stearate 2.0 OMC 1.0 or 4.0 or 7.5 Caprylic/capric triglyceride 10.0 Jojoba 10.0 Microcrystalline wax 6.0 Deionized water qts. to 100

JOURNAL OF COSMETIC SCIENCE 170 similar to the accuracy validation described previously. The absorbance was recorded and the experiment was repeated for fi ve more times. Repeatability of the system. The OMC preparations were weighted (8 g, each) and diluted into 5 μg/ml as above. The absorbance was determined at 310 nm. The practice was done in six replicates. RESULTS AND DISCUSSION VALIDATION OF OMC ANALYSIS METHOD The proposed UV-spectrophotometric determination of OMC was validated in accor- dance with ICH and AOAC guidelines (11,12). The specifi city of OMC determination was evaluated in different solvents: acetonitrile, ethanol, and methanol. The working wavelength (λmax) for OMC determination was found to be 310 nm, resulting in maxi- mum absorbance values, with methanol being the best solvent affording maximized ab- sorption (1) for OMC (4, 8, and 12 μg) without the presence of interference effects. This specifi city profi le was adopted for further method validation. Linearity and range. The validated parameters were assessed at fi ve different concentrations (11,12) of OMC 4, 6, 8, 10, and 12 μg/ml (Table II). This coeffi cient of determination for this range was 0.999 (y = 0.086x – 0.004), which being greater than 0.995 highlights the precision of the method with acceptable linearity (11,12), comparable to that of OMC analysis by HPLC (r = 0.999) at a higher detection limit (10–40 μg/ml 6). Accuracy and precision. The accuracy of the method is highlighted by the recovery (%) of OMC obtained after six analyses. Repeatability of the protocol was demonstrated by re- coveries of 98.23–98.56% as shown in Table III, with these falling within the AOAC set range (12). Method precision was calculated in terms of %RSD, with a %RSD of less than 1 indicating a high level of precision (11). Furthermore, this method exhibited better reproducibility for OMC determination than HPLC (%RSD = 0.59) or micellar electro- kinetic capillary chromatography (MECC %RSD = 1.89) as applied over a wider linear range (0.02–20 μg/ml and 0.25–50 μg/ml 6). VALIDATION OF OMC ANALYSIS METHOD IN SUNSCREEN PRODUCTS Sunscreen products containing OMC (1%, 4%, and 7.5%) in three different dosage forms: O/W and W/O emulsions, and mineral oil were SPF determined (Table IV) to Table II Linearity of OMC Analysis OMC (μg/ml) Absorbance 3.9968 ± 0.0070 0.3434 ± 0.0010 6.0153 ± 0.0030 0.5191 ± 0.0011 8.0377 ± 0.0014 0.6765 ± 0.0008 9.8625 ± 0.0005 0.8528 ± 0.0015 11.8290 ± 0.0046 1.0196 ± 0.0008