The stability of metal–ligand (carboxyl-containing polymer (CCP)) bonding in transition metal complexes is estimated and juxtaposed using Δν(COO) values. The Δν(COO) value is determined from the difference between stretching vibrations of the carboxylate ion in the IR spectra. It is shown that Δν(COO) values for transition metal complexes with ethylenediaminetetraacetic acid (EDTA) increase in the order that directly depends on the order of their stability in the series Fe³⁺ > Cr³⁺ > Cu²⁺ > Ni²⁺ > Co²⁺ > Mn²⁺. The established relationship between the Δν(COO) value and the stability of metal complexes is used to determine the series of metal affinity for carboxyl-containing biopolymers such as citrus pectin (CP) and chitosan succinate (CS). The obtained data indicate that the affinity for metal corresponds to series Cr³⁺ > Cu²⁺ > Co²⁺ > Mn²⁺ > Ni²⁺ for citrus pectin (CP) and to series Cu²⁺ > Cr³⁺ ≈ Ni²⁺ ≈ Co²⁺ > Mn²⁺ for chitosan succinate (CS).

A practical application composite based on mixed chelate complexes [M(S-Ala)₂(H₂O)_n]–[M(S-Phe)₂(H₂O)_n] (M = Cu(II), Zn(II); n = 0–1) as chiral selectors in enantioselective voltammetric sensors was suggested. The structures of the resulting complexes were studied by XRD, ESI-MS, and IR- and NMR-spectroscopy methods. It was determined that enantioselectivity depends on the metal nature and on the structure of the mixed complex. The mixed complexes, which were suggested to be chiral selectors, were stable under the experimental conditions and provided greater enantioselectivity in the determination of chiral analytes, such as naproxen and propranolol, in comparison with the amino acids they comprise. The best results shown by the mixed copper complex [Cu(S-Ala)₂]–[Cu(S-Phe)₂] were: i_pS/i_pR = 1.27 and ΔE_p = 30 mV for Nap; and i_pS/i_pR = 1.37 and ΔE_p = 20 mV for Prp. The electrochemical and analytical characteristics of the sensors and conditions of voltammogram recordings were studied by differential pulse voltammetry. Linear relationships between the anodic current and the concentrations of Nap and Prp enantiomers were achieved in the range of 2.5 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹ for GCE/PEC-[Cu(S-Ala)₂]–[Cu(S-Phe)₂] and 5.0 × 10⁻⁵ to 1.0 × 10⁻³ for GCE/PEC–[Zn(S-Ala)₂(H₂O)]–[Zn(S-Phe)₂(H₂O)], with detection limits (3 s/m) of 0.30–1.24 μM. The suggested sensor was used to analyze Nap and Prp enantiomers in urine and plasma samples.