Polyacrylonitrile-Based Fibrous Sorbents for Sorption-Spectroscopic Determination of Class I-III Toxic Metal Ions: Structure, Functionalisation, and Analytical Performance.

Fibrous polyacrylonitrile (PAN) is a versatile platform for solid-phase analytical chemistry because of its chemically transformable nitrile groups, mechanical robust-ness, and favourable fibre morphology. This review critically examines PAN-based fi-brous sorbents for sorption-spectroscopic analysis (SSA) of toxic metal ions, focusing on polyamine-modified PAN/polyethylenepolyamine/1,2-dichloroethane (PPD) and PAN/polyethylenepolyamine/acrylonitrile (PPA) matrices, iminodiacetate-containing fibrous ion-exchange (FIBAN) fibres, triethanolamine-modified PAN (PAN-T), and electrospun amidoximated PAN nanofibres (AOPAN). Relationships among polymer composition, fibre morphology, surface functionalisation, reagent immobilisation, ion transport, and optical response are evaluated with respect to sensitivity, selectivity, stability, reuse, and practical applicability. Particular attention is given to electrostat-ic/physical versus covalent immobilisation, matrix interference, and the distinction between adsorption capacity and direct solid-phase optical performance. Representa-tive systems include PPD-Arsenazo III for Pb(II), with a minimum detectable concen-tration of 0.24 μg L-1, and AMADA immobilised on a polyeth-ylene-polyamine-modified PAN matrix for Mn(II), with a reported determination limit of 0.02 μg mL-1. The review also considers sustainability, automation, nanostructured architectures, additive manufacturing, and portable optical detection. Current evi-dence indicates that no single PAN architecture is universally superior; future progress requires improved sorbent standardisation, systematic interference and leaching stud-ies, reproducible optical calibration, and validation under realistic sample conditions. Fibre diameter and porosity are also discussed as coupled determinants of diffusion, scattering, and reproducibility.