The applicability of the method to real samples was demonstrated
by analyzing Pb in GBW09305 As and Pb in Cosmetic (cream) reference
material (National Research Centre for Certified Reference Materials,
China) and seven lipstick samples obtained locally. Since the sensitivity
of Pb in various matrices was different, the lipstick samples were analyzed
by isotope dilution and standard addition methods. The emulsion
was prepared using the following procedure. A 0.1-g portion of the lipstick
was 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 at
85 °C for 30 min to melt the lipstick. After cooling, suitable amount of
enriched 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 then
diluted 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 injecting
100 μL of the emulsified solution into the VG system. The concentration
of Pb in the samplewas calculated by the equation described in a previous
paper [26] and/or from the standard addition calibration curve. Owing to
the mass bias effect, the sensitivity of the instrument at different m/z
might be different. Hence, the isotopic composition of Pb in both natural
element and enriched isotope was obtained by determining the intensities
of all isotopes by ICP-MS with solution nebulization.