Determination of Lead in Human Hair by High Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry with Microwave Digestion and Solid Sampling

Abstract

The content of lead in human hair was measured by high resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) combined with microwave-assisted digestion (MAD) and direct solid sampling (DSS). Hair strands were washed, dried, and then cut into three parts (root, middle portion, and tip). For MAD-GFAAS assays, approximately 0.25 g of hair was completely digested using a mixture of concentrated nitric acid and hydrogen peroxide in a closed system. In the DSS-GFAAS assays, 0.1–0.2 mg of dried hair was directly introduced into a graphite furnace using a solid autosampler. The temperature programs were optimized and the effects of various added modifiers were compared. The results indicated that NH₄H₂PO₄ was the optimal modifier for analysis of Pb using GFAAS. Use of the optimal modifier and temperature program gave similar limits of detection for MAD-GFAAS and DSS-GFAAS of 1.16 ng/g and 0.82 ng/g, respectively. Both methods also produced satisfactory recoveries ranging from 98.69% to 103.14%. There was no significant difference observed between the Pb contents of hair strands determined by the MAD-GFAAS and DSS-GFAAS assays, which both indicated that the Pb levels increased along the hair strands. Comparison of the two methods revealed that DSS-GFAAS had several advantageous characteristics over MAD-GFAAS, including the need for much less sample material and having a less time-consuming procedure, lower sample blank absorbance, lower memory effect, and no risk of environmental pollution by digesting chemicals. The direct solid sampling technique can be employed as a good alternative to conventional wet digestion in AAS assays.

Keywords:

• Direct solid sampling
• High resolution continuum source graphite furnace atomic absorption spectrometry
• Human hair
• Lead
• Microwave-assisted digestion

Acknowledgments

This work was supported by grants from the National Natural Science Foundation of China (No. 20907002), the Beijing Nova Program (No. 2009B08), and the Natural Science Foundation of Beijing Municipality (No. 8113031).

Notes

*20 µL of sample solution with 5 µL of 1% (w/v) NH₄H₂PO₄ as a modifier was used for optimization of the furnace heating program.

**0.1–0.2 mg of solid hair sample with 5 µL of 1% (w/v) NH₄H₂PO₄ as a modifier was used for optimization of the furnace heating program.

*Data were given as the average with 95% confidence intervals.

**The certificated samples (about 0.25 g) were digested and diluted to 50 mL, after which they were subjected to GFAAS analyses via liquid sampling.

*Data were given as the averages with 95% confidence intervals.