FLUORESCENT WHITENING AGENTS IN COSMETICS AND LIQUID DETERGENT 283 The ultraviolet absorption spectrum from 210 to 400 nm was used for the qualitative evaluation of the analytes. Qualifi cation of the compound peaks was identifi ed by com- parison with the retention time and the ultraviolet spectra of the standard solutions, and quantities were calculated using response factor of FLD. Figure 2 shows the ultraviolet spectrum of fi ve FWAs standard (210–400 nm). HPLC METHODOLOGY The linear regression equations and the correlation coeffi cients were calculated by the least squares method. The limits of detection and quantization were calculated as three and 10 times the standard deviation of the baseline noise for blank extractions of samples, respectively. The intraday and interday precision were evaluated by analyzing six repli- cates of quality control samples at low, medium, and high concentrations. The accuracy was evaluated as the percent deviation of the mean detected concentrations from the nominal concentrations. Accuracy within ±10% of the nominal concentration and preci- sion with relative standard deviation less than 10% were considered to be acceptable. The recovery measurements were performed in triplicate. The recovery was determined by dividing the value obtained for the sample prepared with the added standard, by the amount added, and then multiplying by 100%. Makeup water, cream, mask, and liquid detergent were employed in the recovery studies. The stability of quality control samples was assessed by analyzing samples stored for 1 week at 4°C and stored for 24 h at room temperature. The samples were considered to be stable when the deviation from the nominal concentration was within ±10.0%. RESULTS AND DISCUSSION EXTRACTION Most of the distyryl-type FWAs were easy to dissolve in water hence, four extraction solvents, including water, water–acetonitrile (2:1, v/v), water–acetonitrile (1:2, v/v), and acetonitrile were selected to optimize the extraction conditions. Meanwhile, effects of different ultrasonic time (10, 20, and 30 min) on the extraction effi ciency of target ana- lytes were also investigated. Compared with extraction with water, lower matrix interference was obtained using water– acetonitrile (2:1, v/v). Because the solubility of FWAs in acetonitrile was inferior to water, the recovery values decreased for excessively high concentration of acetonitrile in extrac- tion solvent (data not shown). Quartz sand was helpful for demulsifi cation to extract the target analytes in emulsion, cream, lotion, and mask samples. Results found that the re- coveries of the FWAs approached equilibrium when the sample was ultrasonicated for 10–30 min. Hence, ultrasonication for 10 min was selected in the next experiment. HPLC Compared with DAD, FLD had higher sensitivity and no response to the substance without fl uorescence characteristics. Thus, using FLD could contribute to reduce the interference

JOURNAL OF COSMETIC SCIENCE 284 Figure 2. Ultraviolet spectrum of fi ve distyryl-type fl uorescent whitening agents (FWA) standard.