PNNL

Abstract

Electrochemical sensors have great potential for environmental monitoring of toxic metal ions in waters due to their portability, field-deployability and excellent detection limits. However, electrochemical sensors employing mercury-free approaches are normally suffered from metal binding competition and fouling by organic substances and surfactants in natural waters, thus tedious sample pretreatments such as wet ashing are needed. In this work, we have developed mercury-free sensors by coating a composite of thiol self-assembled monolayers on mesoporous supports (SH-SAMMS) and Nafion on glassy carbon electrodes. With a combined benefit of SH-SAMMS as outstanding metal preconcentrator and Nafion as antifouling binder, the sensors could detect 2.5 ppb of Cd and 0.5 ppb of Pb in river water, Hanford groundwater, and seawater after 3 and 6 minutes of preconcentration and without sample pretreatment. They could also detect 2.5 ppb of Cd, Pb, and Cu simultaneously after 5 minutes of preconcentration. The electrodes have long life time and excellent single and inter-electrode reproducibility (%RSD of 5 after 8 consecutive measurements). Unlike SAMMS-carbon paste electrodes, the SAMMS-Nafion electrodes were not fouled in samples containing albumin. Successful detection of Cd in human urine was also demonstrated. Other factors including pH effect, diffusion resistance, and Tl interference on the metal detection at SAMMS-Nafion electrodes were studied. With the ability to reliably detect low metal concentration ranges without sample pretreatment and fouling, the SAMMS-Nafion composite sensors have the potential to become the next generation metal analyzers for environmental and bio- monitoring of toxic metals.