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

A VALIDATED OMC ANALYSIS: SPECTROPHOTOMETRIC METHOD 171 monitor their sun protection effi cacies. Obtained UVB absorption effi cacies of 50–87% (13) were based on the presence of OMC as a single UV fi lter, and thereafter all sunscreen products were further analyzed for OMC content. Repeatability of the method. The absorbance values for cosmetic bases used in the SPF deter- minations above were recorded at wavelengths between 200 and 400 nm, with the base- line for each having a smooth pattern and showing no interference over the analytical range. The base was weighted (8 g) for 8 mg/ml OMC that was calculated from 1% OMC in the product. The analytical method is, therefore, specifi c for OMC determination in these prototype sunscreens. The accuracy of OMC levels in these sunscreens was further validated by weighing, conducted on the basis of OMC content at different amounts as described in the Materials and Method section. Recovery values (%) were in the range of 99.76–100.76%, with %RSD being less than 1 as shown in Table IV. Therefore, this analytical method provides an accurate determination of OMC on this basis (11). Inter- estingly, greater recoveries and lower RSD were obtained than in analysis of OMC creams by HPLC (95.6–103.5%, 1.0–2.3% 8), including after extraction using supercritical fl uid (99.55–103.31% 7). Repeatability of the system. OMC sunscreens were subjected to repeat analysis (six times) using the procedure described above. The reproducibility (Table V) was confi rmed by the recovery (%) range (97.23–99.27), and % RSD (0.08–0.50). Table III Accuracy and Precision of OMC Analysis Added amount (μg/ml) Found amount (μg/ml) Absorbance Recovery (%) %RSD The method The system 8.0379 7.8953 0.675 98.23 0.12 0 8.0383 7.9070 0.676 98.37 8.0392 7.9070 0.676 98.36 8.0382 7.9186 0.677 98.51 8.0380 7.9186 0.677 98.51 8.0345 7.9186 0.677 98.56 Table IV Repeatability of the Analytical Method Preparation OMC (%) Recovery ± RSD (%) O/W emulsion 1 99.98 ± 0.06 4 99.76 ± 0.08 7.5 100.04 ± 0.23 W/O emulsion 1 100.02 ± 0.12 4 100.76 ± 0.02 7.5 99.98 ± 0.09 Mineral oil 1 100.04 ± 0.28 4 99.93 ± 0.10 7.5 100.04 ± 0.10