Determination of Lead in Lipstick by Direct Solid Sampling High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry: Comparison of Two Digestion Methods

Abstract

A new analytical procedure for the determination of lead in lipstick has been developed using direct solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry (SS HR CS GFAAS). The performance of this method has been compared to acid digestion methods for sample preparation, with or without hydrofluoric acid (HF) with inductively coupled plasma mass spectrometry (ICP-MS) detection. Good reliability was obtained for all three methods; the results obtained for certified reference materials with concentrations between 1 and 20 ppm were in agreement with the certified values. However, for materials with complex matrices, such as pearl or Ca-Na borosilicate, only ICP-MS with HF sample digestion or AAS with direct solid sampling allowed complete recovery of lead. To avoid the use of hazardous acids, the development of SS HR CS GFAAS is an interesting alternative. With the AAS method, a characteristic mass of 13.2 pg of lead was obtained, and the limit of detection was 0.005 µg/g. The performance of the method was evaluated by determining lead in lipstick. The use of the solid sampling technique constitutes a good alternative for accurate and rapid determination of lead content in lipstick and cosmetic raw materials, with a suitable limit of detection and a reduced risk of contamination or of analyte loss. Another alternative would be to use ICP-MS determination in conjunction with microwave-assisted acid digestion without the use of HF, which implies accepting a quantification of “nearly total” lead, closer to a “bio-extractible” fraction.

Keywords:

• Cosmetics
• Direct solid sampling analysis
• High-resolution continuum source atomic absorption spectrometry
• Inductively coupled plasma mass spectrometry
• Lead
• Microwave digestion

Acknowledgments

The authors thank Solenn Mollot, Gessy Duboeuf, and Franziska Reeder for technical assistance and discussions. This work cannot be realized without the help of Stéphane Arditty and Bernadette Leguidcoq for the specially tailored lipstick formulations.

Notes

^a Each value is the mean of at least 3 replicates ±ts/√n where t is the Student's t-distribution value for a probability level of 95%, s is the standard deviation, and n is the number of replicate determinations.

^b Recovery factor = (found value/certified value) 100 ± confidence interval.

^c For Zeolite 1, the certified lead concentration is 20.80 ± 0.40 ppm ; for MESS-3 the certified value is 21.10 ± 0.70 ; for TiO₂ SRM the noncertified concentration is 1.10 ppm.

^a Each value is the mean of 3 to 4 replicates ±ts/√n where t is the Student's t-distribution value for a probability level of 95%, s is the standard deviation, and n is the number of replicate determinations.