Novel Colorimetric Method for Simultaneous Detection and Identification of Multimetal Ions in Water: Sensitivity, Selectivity, and Recognition Mechanism

Accurate recognition and speciation analysis of heavy-metal ions in complex hydrological environments is always a serious challenge. In this work, we proposed a small-molecule-based ultrasensitive colorimetric detection strategy and successfully applied it to the accurate detection of Fe²⁺, Fe³⁺, Co²⁺, and Hg²⁺ in groundwater through the specific recognition of multiple ligands of different metal ions. The detection limits for Hg²⁺, Co²⁺, Fe²⁺, and Fe³⁺ are calculated to be 6.51, 0.34, 0.49, and 1.01 ppb, respectively, which are far below the drinking water standards and superior to most of the reported colorimetric sensors. Remarkably, the speciation analysis of Fe²⁺/Fe³⁺ also has been successfully realized by a one-step method without complex pretreatment. The speciation and concentration of Fe²⁺ and Fe³⁺ in actual water samples can be accurately identified and monitored. In addition, as an attempt of visual onsite detection, we have developed a simple test strip, which has been applied to visual monitoring of four metal ions with the detection limit estimated by the naked eye to be as low as ppb level. This proposed colorimetric method realizes the rapid, sensitive, and portable multiple metal ions recognition and Fe²⁺/Fe³⁺ speciation analysis, displaying great potential for onsite rapid water quality analysis.