Calibration strategies for the direct determination of rare earth elements in hard disk magnets using laser-induced breakdown spectroscopy

Abstract

This study is dedicated to the direct determination of base (B and Fe) and some rare earth elements (REE; Dy, Gd, Nd, Pr, Sm and Tb) in hard disk magnets. Five calibration strategies were tested and compared. Two of them are related to multivariate calibration: multiple linear regression (MLR) and partial least squares (PLS). Both presented adequate trueness values within a range of 80–120% for almost all analytes. The only exception was Tb, which was probably due to matrix effects. The use of MLR and PLS permits the testing of calibration models in the presence of interference, but matrix effects are not corrected. Because of this, three other univariate calibration methods were also tested and compared: multi-energy calibration (MEC), one-point gravimetric standard addition (OP GSA) and two-point calibration transfer (TP CT). These three calibration approaches permit matrix effects corrections, but an appropriate selection of the blank and standard is mandatory. The standard error obtained ranged from 0.01 to 6% using these univariate calibration methods.