The purpose of this work is to report an analytical procedure to prove the validity of the hypothesis of the representativeness of the mass vaporized in the plasma plume of the studied sample. To achieve that, we used the laser induced breakdown spectroscopy (LIBS) technique to analyze some minerals and trace elements in cow tail hair. First, hair samples were dissolved in nitric acid; then the solutions were analyzed by atomic absorption spectrometer. Ca, Mg, and Na mass concentrations were determined for the 25 hair samples. Finally, a small amount of hair from every strand was cut in very small pieces and mixed with potassium bromide to make 12 mm diameter pellets. The laser was focused on the pellet surfaces, and the intensities of the emission lines of the studied elements were related to their absolute mass concentrations already measured. Experimental conditions were chosen to guarantee the reproducibility of ablations and to minimize the fluctuations of the ablated mass. In addition, local thermodynamic equilibrium was verified to prove the possibility of use of the theoretical model to obtain the variation of the emission line intensity as a function of the species concentration in the plasma plume.