Calcium evaluation of human fingernail using laser plasma spectroscopy by simultaneously applying addition and modified external standardizations

Identification and quantification of human fingernail calcium is demonstrated by laser-induced breakdown spectroscopy (LIBS) using the modified external standardization. Since cow’s horn and hoof have structures very similar to the fingernail, either of them is individually selected as the matrix of standard samples. In total, 12 standard samples for each matrix are prepared using CaCO3 as the standard substance. In order to achieve accurate calibration curves associated with the method of modified external standard, foremost, the calcium concentration of each of matrices (horn and hoof) is determined by the method of standard additions. The results indicate that there exist 4887 μg/g (ppm) and 4156 μg/g (ppm) of calcium in the pure horn and hoof matrices, respectively. Then, the external calibration curves related to the two matrices are plotted using the information of standard samples. Finally, by the use of signals obtained from LIBS experiment for three different fingernails and inserting their amounts into the calibration curves, the calcium concentration of the fingernails under test is measured to be 10,814 μg/g (ppm), 13,106 μg/g (ppm) and 14,974 μg/g (ppm). The difference of the calcium concentrations between three specimens, as will be discussed, may be due to different physical conditions of people who have donated their fingernails.