|
The active ingredient in skin whitening products has been measured using a microdialysis sampling technique linked to HPLC. As perfect as we are in all our diversity, the human race strives to change itself to achieve what it regards as perfection. This has manifested itself in many ways throughout history. One of the more severe practices was physical deformation, including neck stretching, earlobe stretching and body piercing, although the latter custom is popularised today by western youth culture. Another common tradition is skin colouring, which was once carried with dyes but today helps to sustain the cosmetics industry. This practice varies from the simple application of foundation, blusher and eye shadow to permanent changes of skin colour. Skin whitening is popular in Japan and other Asian countries and is exemplified by the traditional make up worn by geishas. Nowadays, however, many Asian women desire the "western" look and go to greater lengths, applying skin depigmentation agents to achieve more permanent results. In other countries too, people lighten their skin. In the US, racially white central European women have used skin whitening to appear as white as Anglo-Saxon women. One of the more common depigmentation agents is arbutin, known chemically as p-hydroxyphenyl beta-D-glucoside. It occurs naturally in the leaves of cranberry, bearberry, and blueberry shrubs and works by blocking the enzyme that produces the pigment melanin. It has also been used to prevent liver spots and freckles and to treat sunburn marks and allergic inflammation of the skin. In skin whitening preparations, low concentrations have no effect but relatively high concentrations have been known to cause irritation to the skin. The statutory level in Taiwan, where these products are common, is 7%. However, Taiwanese researchers led by Yeou-Lih Huang from the Kaohsiung Medical University have declared that there is no simple analytical method for measuring arbutin levels in commercial products. Most current protocols involve time-consuming sample preparation before the measurement step, so they have devised a method based on microdialysis linked online to HPLC. After optimising the method on standard solutions of arbutin, the method was used to analyse three commercial whitening products (cream, lotion and essence) purchased from local drug stores. The products were diluted with water and subjected to microdialysis using high-purity water as the perfusing liquid in the microprobe. Arbutin molecules diffused from the product solution into the probe via a membrane and were detected by HPLC with UV detection at 254 nm. The HPLC eluent was 40% methanol in 0.02 M aq. phosphate buffer at pH 5.5. The retention time of arbutin was 3.05 min and there were no coeluting substances to interfere with its detection. The detection limit was 15 micromolar and the calibration curves were linear over the range 0.1-20 mM. Precision and accuracy were both acceptable and the analysis time was 26 min/sample. Certified contents of arbutin were declared for the lotion (5 wt.%) and the cream (3 wt.%), but not for the essence. The measured concentrations were 4.95 and 3.04 wt.%, respectively. The method was also validated by comparing the results with those obtained by the no-net-flux method, a well-established calibration technique for microdialysis. This comparison confirmed the accuracy of the new technique and the content in the essence was 0.83 and 0.85 wt.% by the new and no-net-flux methods, respectively. The critical parameters of the analysis were the eluent pH, which cannot be too acidic because it hydrolyses arbutin to glucose and hydroquinone, and the perfusate flow rate, low values of which affected recoveries from the product. This simple, one-step method uses low amounts of organic solvent and requires very little sample preparation, so is suitable for the routine and regular determination of arbutin in whitening products. Related links:
|
 |
