Temperature-assisted stabilization of aqueous polychlorinated biphenyl stock solutions for sorption experiments

Aqueous stock solutions of hydrophobic organic contaminants such as polychlorinated biphenyls (PCBs) are commonly used in laboratory sorption studies, yet their preparation and short-term stability are rarely described in sufficient detail. Because PCB congeners have high hydrophobicity and strong affinity for surfaces, apparent concentrations in aqueous stock solutions can change during storage and handling. This protocol describes a practical procedure for preparing, stabilizing, extracting, and analytically verifying aqueous PCB stock solutions prior to batch sorption experiments. The approach combines closed-bottle thermal equilibration, controlled hydrodynamic mixing, minimized plastic contact, sequential cyclohexane extraction, and congener-specific GC-ECD calibration. Validation using independently prepared stocks shows that heating and mixing increase the summed concentration of eight indicator PCB congeners after storage, while recovery testing demonstrates that two sequential extractions recover 94.8-99.5% of the cumulative three-extraction PCB concentration. The protocol is intended for laboratories working with technical PCB mixtures where reliable initial PCB concentration is required before sorption or kinetic studies.