Combining advanced oxidation principles and electrochemical detection for indirect determination of phosphonate in scale inhibitors employed in the oilfield

The oilfield urges efficient and low-cost scale management. Specifically, simple and accurate methods to determine the active component of scale inhibitors at the point of need can be a game-changer by preventing their misuse, ultimately reducing time and expenses. To address this bottleneck, we describe an electrochemical method for the indirect monitoring of phosphonate (PO3) scale inhibitors based on advanced oxidation processes principles. PO3 species are first converted to phosphate (PO4) via UV exposure (3 min) in the presence of an oxidant, which is then allowed to react with ammonium molybdate to instantaneously form an electroactive phosphomolybdate complex. Next, the electrochemical detection of this complex is proceeded by interrogating scalable miniaturized three-electrode Au sensors, with SU-8 photoresist film individually delimiting the active area of the electrodes to guarantee their reproducibility. An average error of 7.3% was obtained over the analyses of standard samples (H3PO4) for 6 months by different operators. The approach reached accuracies from 81.5 & PLUSMN;8.3 to 100.3 & PLUSMN;15.5% when assessing nine commercial scale inhibitor samples. These results are an encouraging indicator that our method is a promising tool for on-site, fast, and accurate quality control of phosphonate scale inhibitors.