Syringe Pressure-Assisted Switchable Hydrophilicity Solvent Microextraction with Smartphone Digital Image Colorimetry: A Rapid Method for Trace Cobalt Determination

Abstract

Heavy metal pollution poses a major threat to 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. Additionally, an AGREE for sample preparation (AGREEprep) score of 0.75 indicates its remarkable environmental effectiveness and prominent eco-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 an efficient, simple, and low-cost method for the direct field analysis of Co2+ in water samples, as well as for determination Co2+ in environmental, medicinal plant, and biological samples.