Solid-Phase Extraction Combined with Digital Image Colorimetry for the Analysis of Lead in Water Samples

In this study, we developed a rapid method for determining lead(II) by integrating solid-phase extraction with digital image colorimetry to reduce the time and labor required for the analysis of lead(II) in water samples. The solid-phase extraction column was packed with cellulose as a bio-based adsorbent, which facilitated adsorption and enrichment of lead(II) during sample loading. The elution step, which is time-consuming and solvent-intensive, was eliminated from the procedure. An aqueous solution of sodium rhodizonate was added to react with lead(II), forming a red–brown complex. The color intensity was quantified using a smartphone-based digital image colorimetry. The method showed good linearity in the range of 0.01–0.8 mg L−1 with R2 > 0.99. In tap, river, and spring water, the recovery was 93.5% to 97.5% with a relative standard deviation of 1.7–4.8%. Five complementary greenness assessment tools confirmed the environmental friendliness of the method. This rapid pretreatment and detection technique can be applied to analyzing lead(II) in aqueous samples.