Multiway Calibration Strategies in Laser-Induced Breakdown Spectroscopy: A Proposal.

In this study, a new approach to laser-induced breakdown spectroscopy (LIBS) data modeling using multiway algorithms was investigated. Two case studies, parallel factor analysis (PARAFAC) and unfolded-partial least-squares with residual bilinearization (U-PLS/RBL) algorithms were used in (1) the determination of Al, Cu, and Fe in samples of reference material of printed circuit board (PCB) from electronic waste and (2) the determination of Ca, K, and Mg in samples of a human mineral supplement, where depth was used to obtain multidimensional data in the first case and delay-time in the second. In addition, univariate calibration was applied and compared with the multiway approaches. In all cases, the calibration data set was prepared from salts. PARAFAC showed satisfactory results in the first study, with low prediction errors and good accuracy for most samples, and the U-PLS/RBL algorithm presented the best performance for mineral supplement samples.

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

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.

Spectroanalytical method for evaluating the technological elements composition of magnets from computer hard disks.

In this study, inductively coupled plasma optical emission spectrometry (ICP OES) was used for the development of an analytical procedure for elemental analysis of hard disks (HDs). More than 50 samples were acquired and separated according to the manufacturers. Both magnets were used, namely, the actuator (a) and the spindle (s) motor. The samples were heated to remove magnetism, ground in a knife mill and sieved. Different digestion procedures were performed with a block digester and microwave, and three acid concentrations were employed. Due to the lack of certified materials or references from HDs, tests of standard addition and recovery were performed to verify the accuracy of the proposed method. Hyperspectral image and principal component analysis were also used to assist in the data treatment related to the Ni layer. For both magnets, the best analytical procedure was 100 mg of sample, 7 mol L-1 nitric acid and a digester block. The elements observed in the highest concentrations were Fe followed by Nd and Pr. This procedure was simpler than others were and prioritized the principles of green chemistry.