Reagent filming for simplifying multistep sample preparation and separation of metal ions based on displacement magnetic solid phase extraction

Sample pre-treatment of aqueous samples (such as pH adjustment, reagent addition, mixing, and incubation) is an essential step in most analytical assays. To perform these steps, weighing, diluting, and pipetting reagents for adjusting the physicochemical conditions of the sample before extraction are required. In this work, we propose a simpler pathway that involves the entrapment of premeasured, premixed reagents and materials within polyvinyl alcohol (PVA)-based, water-soluble films. The reagent films, produced through a simple and scalable cast-drying process, provide a glassy inner matrix that can encapsulate and stabilize reagents (such as acids and complexing agents) and a sorbent material (stearate coated-CoFe 2 O 4 magnetic nanoparticles). When dissolved in water, the film releases its contents, enabling the adjustment of sample pH, the complexation of metal ions, and the extraction of metal chelates in a single step that would otherwise require several discrete steps through batch sample processing. As proof-of-concept and by capitalizing on a displacement reaction, Cu 2+ and Ni 2+ as model species were extracted from aqueous solutions with minimum user effort that only involves the addition of the PVA reagents film and mixing. Once the procedure is completed, the magnetic nanoparticle sorbent is collected and eluted for subsequent analysis accomplishing satisfactory analytical features (recoveries 85–114%, RSD < 12%), good selectivity and adequate sensitivity that enables the determination of metal ions at concentration levels that meet legislative requirements set by international organizations such as WHO and US EPA (Cu 2+ < 2 mg L −1 and Ni 2+ < 70 μg L −1 ). Overall, this approach advances sample preparation by streamlining treatment steps and facilitating extraction and could also be adopted for on-site sample preparation.