Quantitative determination of calcium, magnesium, and zinc in fingernails by laser-induced breakdown spectroscopy

Quantitative determination of Ca, Mg, and Zn in fingernails was performed with laser-induced breakdown spectroscopy. Two different methods of producing solid standards for calibration were explored – preparation of keratin pellets and deposition of aqueous solutions to filter papers. Measurements of the temperature and electron density of the plasma produced on keratin pellets, filter paper, and nails were performed, and it was determined that the standards prepared on filter paper gave plasma temperatures and electron densities closer to those observed on the nails. The ablation rate of the filter paper was also more similar to that of the nails. Using calibration curves produced using these filter paper standards, Ca, Mg, and Zn were determined in fingernails of 11 subjects. For comparison, the same samples were digested and atomic absorption was used to determine the same three elements. The differences in results are discussed in light of sample homogeneity and instrumental precision; the best agreement was obtained for determination of Zn. The work suggests that the filter paper method of standard preparation may be appropriate for LIBS analysis of other samples that give relatively low temperature, low electron density plasmas (i.e., polymers).