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The applicability of the method to real samples was demonstratedby analyzing Pb in GBW09305 As and Pb in Cosmetic (cream) referencematerial (National Research Centre for Certified Reference Materials,China) and seven lipstick samples obtained locally. Since the sensitivityof Pb in various matrices was different, the lipstick samples were analyzedby isotope dilution and standard addition methods. The emulsionwas prepared using the following procedure. A 0.1-g portion of the lipstickwas transferred into a 10 mL flask. 0.5 mL 10% m/v Triton X-100,0.05 mL HNO3 and 5 mL H2O were added. The solution was heated at85 °C for 30 min to melt the lipstick. After cooling, suitable amount ofenriched isotope or Pb element standard solution (0.1–2 ng mL−1),K3Fe(CN)6 and a drop of antifoam were added, the emulsion was thendiluted to themarkwith purewater. A blank solutionwas also prepared,as outlined above, to correct any Pb in the reagents used for sample preparation.These solutions were analyzed for Pb using ICP-MS by injecting100 μL of the emulsified solution into the VG system. The concentrationof Pb in the samplewas calculated by the equation described in a previouspaper [26] and/or from the standard addition calibration curve. Owing tothe mass bias effect, the sensitivity of the instrument at different m/zmight be different. Hence, the isotopic composition of Pb in both naturalelement and enriched isotope was obtained by determining the intensitiesof all isotopes by ICP-MS with solution nebulization.
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