Matrix-matched calibration material for zinc analysis of human nails by laser-induced breakdown spectroscopy

Zinc is an element required in multiple biochemical processes in the human body as a structural, regulatory or catalytic ion. Its deficiency is linked to issues of a variety of health processes such as physical growth, immune system, or reproductive functions to name a few. Its quantitative determination using Laser-Induced Breakdown Spectroscopy (LIBS) on fingernails as a proxy has been proposed by many studies. In this study, a solid matrix-matched material was developed as a reference material for this type of analysis. A solution of alginic acid and keratin, spiked with zinc oxide nanoparticles, was cross-linked and dried to obtain a hard film. The calibration curve showed a determination coefficient of 0.986, Zn limit of detection of 13 μg.g⁻¹ and limit of quantitation of 27 μg.g⁻¹. The calibration curve was used on two toenails and the Zn concentration was confirmed by bulk ICP-MS. These results confirmed the potential for LIBS to be used for the quantitative diagnostic of Zn in fingernails using these adapted matrix-matched reference materials.