Lead detection in environmental water sample using an organoclay film-based attenuated total reflectance sensor

A novel, portable and cost-effective optical sensor for lead detection in water has been developed, which combines a miniature sensing platform based on multiple internal reflection attenuated total reflectance (MIR-ATR) with a one-step synthesized thiolated organoclay thin film. This film is highly effective for the sequestration and pre-concentration of Pb2+ ions. Lead was detected with high sensitivity achieved through the combination of multiple internal reflections and large Pb2+ uptake capacity of the organoclay after forming bright yellow lead-thiolate (PbSx) complexes within the film. Un-optimized detection limits of 200 ppb Pb2+ in deionized water samples and slightly higher in Pb2+-spiked natural water samples were measured. The sensor response was reasonably fast and depended on the Pb2+ solution flow rate. The Pb2+ uptake at equilibrium was greater at slower flow rates, as Pb2+ ions require longer times to enter the galleries of the organoclay film and bind to the thiol groups. Operation of the sensor over pH values ranging from 5.0 to 7.0 appeared optimal for maximum sensitivity and longevity of the organoclay films. Lead-loaded films could resist up to 10 recycling treatments with acid before film degradation occurred.