Syringe pressure-assisted switchable hydrophilicity solvent microextraction with smartphone digital image...

Heavy metal pollution poses a major threat to the global environment and public health. Current methods for detecting heavy metals require expensive instruments and laborious operations, calling for simple and rapid detection methods. In this work, disodium terephthalate (C₈H₄Na₂O₄) was used for the first time as a switchable hydrophilicity solvent, with a syringe serving as the extraction chamber, thereby establishing a syringe pressure-assisted switchable hydrophilicity solvent microextraction (SPA-SHS-LPME) method. The color changes of the cobalt-extracted solution were captured by a smartphone and processed via smartphone digital image colorimetry (SDIC) to establish a quantitative relationship between color intensity and Co²⁺ concentration. This method enables the extraction and detection of Co²⁺ in various real samples within 4 min. Under optimal conditions, the established method achieved an enrichment factor (EF) of 23, with a limit of detection (LOD) of 7.50 µg L^-1. Additionally, an AGREE for sample preparation (AGREEprep) score of 0.75 indicates its remarkable environmental friendliness. Owing to the use of a syringe and a smartphone as the core components, the entire assembly is compact, lightweight, and can be readily integrated into a portable suitcase, offering excellent portability for on-site operation. This work provides a detection method featuring rapid analysis speed, simple operation, low-cost and good portability, which can be used for the direct on-site analysis of Co²⁺ in water samples, as well as the screening and on-site monitoring of complex matrix samples.