CAFFEINE IN HAIR-CARE AND ANTICELLULITE COSMETICS 257 for transdermal delivery. By heating, it gives a viscous solution which is unsuitable for application to the SPE cartridge. Therefore, to remove carbomer, an additional procedure must be applied to the preparation of anticellulite gels. Thus, the samples were dissolved in 96% ethanol, and after vortex-mixing, 0.5 mL of 0.1M NH4OH was added to obtain Figure 4. Chromatogram of anticellulite gel 1 extract on the HR-X cartridge at 260, 270, and 2 74 nm caffeine retention time 3.35 min. Table I Chromatographic and Analytical parameters of the Method Chromatographic parameters Retention time (min) Capacity factor (k’) Peak symmetry Peak width Theoretical plates (N) Resolution Selectivity 3.34 ± 0.007 1.11 0.81 0.108 5,781 5.62 2.25 Analytical parameters Range (mg/ mL) Slope Intercept R2 LOD S/N (1:3)c LOQ S/N (1:10)c 0.01–0.2a 13,971.6 20.04 0.9997 0.007% 0.02% 0.08–1.6%b – – – – – a Concentration in fi nal extracted solutions . b Assumed content in cosmetic products . c S/N ratio for LOD and LOQ expressed as spiked caffeine content in shampoo sample .

JOURNAL OF COSMETIC SCIENCE 258 pH 7–8. In this weakly alkaline solution, carbomer was precipitated as a white solid clod which was further separated by centrifugation (22). OPTIMIZATION OF SPE PROCE DURE Optimization of the SPE p rocedure included cartridge and solvent selection, as well as extraction recovery evaluation. Caffeine is soluble in methanol therefore, this solvent was selected for elution. The cartridge was selected based on the extraction yields obtained for standard solutions and real samples on each type of the tested sorbents. A known amount of caffeine standard solution, at three different concentration levels (0.01 mg/mL, 0.02 mg/mL, and 0.1 mg/mL) which corresponded to caffeine content of 0.02%, 0.04%, and 0.2% in cosmetic product was extracted on different cartridges, and the extraction yield was calculated as the ratio of the loaded and eluted caffeine. The percentage extraction yield was found to be 84–90% for HR-X cartridges, whereas for the other types of car- tridges, these values were lower. Thus, for examined cartridges, recoveries were 70–77% on C18, 68–75% on C18ec, 75–86% on C18 Hydra, and 80–90% on C8. However, the fi nal cartridge selection also depended on the sample matrix therefore, the extraction yield test was made for all real samples on fi ve cartridges. Also, the chromatographic parame- ters obtained for these extracts were analyzed. The results showed that the highest chro- matographic peak purity, peak area, and concentrations of caffeine from all real samples except hair balsam were obtained on HR-X cartridges. The octadecyl modifi ed silica endcapped cartridge (C18ec) was eliminated because an opalescent solution was obtained after eluting with methanol. Also, some ingredients of the viscous shampoos clogged C18ec and C18 cartridges, and the fl ow of the sample was diffi cult. A similar situation was found for the hair balsam extraction on C18ec, C18, and C18 Hydra cartridges. In Table II, chromatographic peak areas obtained for the examined cosmetics on different cartridges were presented. An HR-X cartridge was selected for the extraction and clean-up because it allows fast sample fl ow and high extraction yields. Only for hair balsam, the C8 car- tridge was used because of a signifi cantly higher peak area for caffeine. ANALYTICAL PARAMETERS The calibration line for caffeine determination was constructed by plotting the peak areas versus the concentration of the standard solution. A least-squares linear regression analy- Table II Average Caffeine Peak Area Obtained on Different Cartridges Product Peak areas ± SDa HR-X C18 Hydra C8 Anticellulite gel 1 2,702.7 ± 75.4 715.6 ± 46.1 594.9 ± 42.8 Anticellulite gel 2 1,195.2 ± 80.3 442.1 ± 52.7 180.6 ± 20.6 Shampoo 1 1858.5 ± 182.6 911.4 ± 38.4 450.3 ± 40.9 Shampoo 2 1772.0 ± 130.4 1730.8 ± 105.9 604.9 ± 51.4 Hair balsam 1,375.1 ± 95.2 – 1748.2 ± 78.5 a SD of three measurements .