Simultaneous determination of six polyhydroxyl compounds in cosmetics and toothpaste using high performance liquid chromatography with evaporative light-scattering detection

With the full implementation of the cosmetic formula ingredient registration system and the standardized management of labels and identification, the ingredients registered and declared on the label must be consistent with the actual ingredients contained in the product. Further, cosmetic manufacturers require accurate determination of the ingredients in cosmetics for formula analysis. Therefore, a method for the simultaneous determination of six polyhydroxyl compounds, Pro-Xylane, xylitol, sorbitol, mannitol, sucrose, and inositol, in cosmetics and toothpaste was established. According to this method, approximately 0.5 g of the sample was weighed into a 25 mL centrifuge tube. Water-dispersed and oil-in-water cosmetic samples were extracted using 10 mL water, followed by washing with 5 mL <i>n</i>-hexane and 5 mL ethyl acetate. The water-in-oil cosmetic samples were predispersed in 5 mL ethyl acetate, extracted using 10 mL water, and washed with 5 mL <i>n</i>-hexane. After filtration through a 0.22 μm membrane, the extracted solution was subjected to separation using an Ultimate XB-NH₂ column (250 mm×4.6 mm, 5 μm), employing gradient elution with acetonitrile and distilled water as the mobile phases. This was followed by detection using evaporative light-scattering detector (ELSD) and quantification using the external standard method. Optimization experiments were conducted to select chromatographic columns, extraction processes, and chromatographic conditions. Specifically, the Ultimate XB-NH₂ column and Ultimate XB-C₁₈ column were compared in terms of separation efficiency. Based on the separation efficiency and analysis time, the XB-NH₂ column was found to be more suitable as the separation column for this method. The effects of trichloromethane (TCM), ethyl acetate (EA), and <i>n</i>-hexane as predispersants and washing solutions were compared. Among them, the combination of ethyl acetate and <i>n</i>-hexane was found to be more suitable owing to its effective pre-dispersion capability and ability to remove both polar and nonpolar compounds from the extraction solution. The instrumental conditions were optimized using the gradient elution mode with acetonitrile and water as the mobile phase. The column temperature was set at 20 ℃, while the drift tube temperature and atomized gas pressure were set to 60 ℃ and 0.17 MPa, respectively. Under the optimized conditions, the method was validated in terms of linearity, sensitivity, recovery, and repeatability. The results showed that the six polyhydroxyl compounds exhibited excellent linearities within the range of 0.2-5.0 g/L, with correlation coefficients in the range of 0.991-0.996. Sensitivity is expressed as the limits of detection (LODs, <i>S/N</i>=3) and quantification (LOQs, <i>S/N</i>=10). The LODs and LOQs were 0.10% and 0.35%, respectively. Recovery tests were conducted at three levels (low, medium, and high) for oil-in-water cosmetics, water-in-oil cosmetics, and toothpaste matrices. Samples were extracted and measured six times in parallel. The average recoveries of the analytes were 84.7%-94.1%, with relative standard deviations (RSDs, <i>n</i>=6) of 2.2%-6.9%. Finally, the proposed method was employed to analyze six polyhydroxyl compounds in cosmetics and toothpaste that were randomly purchased from a local market. Sorbitol and xylitol were found to be the most commonly used ingredients in toothpaste, while Pro-Xylane was more common in whitening cosmetics. This method has the advantages of simplicity, stability, reliability, and good reproducibility and is suitable for the detection of polyhydroxy compounds in cosmetics. This method effectively addresses the current issue of inadequate detection of polyhydroxyl compounds in cosmetics.