Voltammetric Sensor for General Purpose Organohalide Detection at Picogram per Liter Concentrations Based on a Simple Collector−Generator Method

With the aim of producing a general purpose sensor for environmental analysis, we describe a simple and sensitive method for organohalide detection, based on an electrochemical collector−generator process. The sensor consists of four coplanar electrodes contacting a solution volume of 300 μL, containing organohalide. At the first working electrode (a Zn/PTFE composite), the analyte is electrolyzed to liberate halide ions. At the second working electrode (Ag), the halide ions are detected by cathodic stripping voltammetry. Using a preconcentration time of 600 s, with differential pulse voltammetry for stripping, the responses to 1-chloropropane, chloroform, carbon tetrachloride, iodoethane, and bromoethane can be plotted on a common calibration curve, with a detection limit of 0.1 nM (1.3 pg L-1 or less depending on the organohalide). To the best of our knowledge, this is the lowest reported organohalide detection limit by an electrochemical method and is so far the only general purpose electrochemical method sensitive enough for regulatory requirements. The sensor response was invariant for ∼40 measurements. Analysis of tap water, spiked with chloroform or carbon tetrachloride, gave recoveries within 1.0−2.6% of the recoveries by the standard GC method.