<b>Principal component analysis (PCA) was used to obtain information about the number of components in the complex formation equilibria of Co<sup>2+</sup> and Ni<sup>2+</sup> with glycine (Gly). In order to obtain a clearer insight into these complex formation systems, multivariate curve resolution-alternating least squares (MCR-ALS) was used. Using MCR-ALS as a soft-modeling method, well-defined concentration and spectral profiles were obtained under unimodality, non-negativity, and closure constraints. Based on the obtained results, an equilibrium model was proposed and subsequently, a hard-modeling method was used to resolve the complex formation equilibria completely. Due to the presence of multiple equilibria, the resolution of such systems is very difficult. The Co-Gly system was best described by a model consisting of M(GlyH), M(Gly), M(Gly)<sub>2</sub>, M(Gly)<sub>2</sub>H, and M(Gly)<sub>3</sub> (M = Co<sup>2+</sup>) with the overall stability constants determined to be 7.10 ± 0.011, 5.14 ± 0.006, 9.28 ± 0.009, 13.75 ± 0.016, and 11.10 ± 0.010, respectively. On the other hand, the system of Ni-Gly was best fitted by a model containing M(GlyH), M(Gly), M(Gly)<sub>2</sub>, M(Gly)<sub>3</sub>, and M(Gly)<sub>2</sub>(OH) (M = Ni<sup>2+</sup>) with overall stability constants of 10.95 ± 0.04, 6.41 ± 0.03, 11.31 ± 0.03, 15.39 ± 0.06, and 14.32 ± 0.02, respectively.</b>

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