Portable one-step effervescence tablet-based microextraction combined with smartphone digital image colorimetry: Toward field and rapid detection of trace nickel ion

In this study, the one-step switchable hydrophilic solvent (SHS)-based effervescence tablet microextraction (ETME) was coupled with smartphone digital image colorimetry (SDIC) for the field detection of nickel ion (Ni²⁺) for the first time. Both extractant and CO₂ were generated in situ when the novel SHS-based effervescence tablet was placed in the sample solution. The complexant 1-(2-pyridinylazo)-2-naphthaleno (PAN) dissolved from the effervescence tablet to form a stable complex with Ni²⁺, and the extractant was uniformly dispersed in the sample solution under the action of CO₂ and fully in contact with Ni-PAN, which enabled efficient extraction of Ni²⁺. The color changes of the extraction phase were captured by smartphone, then a quantitative relationship between the concentrations of Ni²⁺ and color intensity of images captured using a smartphone was established by customized applet WASDIC, which realized quantitative analysis of Ni²⁺ in different samples. Under optimal conditions, the enhancement factor (EF) of the proposed method was 65.1, the limit of detection (LOD) and limit of quantification (LOQ) were 1.69 and 5.64 μg L^-1, respectively. The developed method was successfully applied to the detection of trace Ni²⁺ in the environmental samples and natural medicines. And the applicability of the method for use in field analysis was validated.