ORIGINAL ABSTRACT

Emerging contaminants (ECs), such as pharmaceuticals and agrochemicals, persist in aquatic systems and are often underestimated by targeted chromatographic methods that quantify only compounds with available analytical standards. Here, we present a portable electrochemical platform based on laser-induced graphene (LIG) and screen-printed graphene (SPG) electrodes, which couples hydrogen peroxide-assisted redox mediation with chronoamperometric detection to quantify the cumulative burden of oxidizable organic contaminants in water. Using amoxicillin (AMX) as a model compound, the system achieved sub-ppb sensitivity (LOD = 0.085 ppb) with excellent linearity (r2 > 0.99) across a wide dynamic range and strong agreement with HPLC-MS analysis. Under optimized electro-Fenton (EF) conditions, additional ECs─including diclofenac, ibuprofen, glyphosate, and estradiol─showed comparable responses, demonstrating broad applicability independent of molecular structure. Mass spectrometry confirmed peroxide-driven radical transformation of AMX, revealing hydroxylated derivatives and β-lactam ring-opened intermediates consistent with reactive oxygen species (ROS) chemistry. Unlike targeted chromatographic approaches, the electrochemical signal reflects the integrated pool of peroxide-reactive species, including transformation products not directly quantified by conventional methods. Application to real wastewater samples showed that the EF-assisted electrochemical response captures a broader oxidizable organic load than targeted HPLC-MS/MS. These findings establish peroxide-assisted graphene electrodes as a sensitive, low-cost, and field-deployable platform for rapid screening of total oxidizable contaminant burden in complex water matrices.