聚乙烯醇-碘法在线测定表面处理槽液中硼酸含量

A novel method based on reaction kinetics and in-situ spectroscopic analysis was developed for the online rapid detection of boric acid in metal surface treatment bath solutions.This method systematically investigated the kinetic behavior of the chromogenic reaction between polyvinyl alcohol(PVA) and triiodide ions(I~-3) in the presence of boric acid.By adjusting parameters such as reactant concentration, medium composition, and temperature, and monitoring the temporal changes in the solution absorption spectrum, it was found that the inherent sulfuric acid and sodium ions in the system significantly promote the PVA-I~-3 chromogenic reaction, with lower temperatures being more favorable for the reaction to proceed.Based on these findings, the reaction temperature was precisely controlled at 20 ℃,and the sulfuric acid concentration and electrostatic environment in the reaction medium were optimized.This approach significantly accelerated the boric acid concentration-dependent PVA-I~-3 chromogenic reaction while effectively suppressing interference from background components in the bath solution.A reliable analytical signal suitable for quantification was obtained within 120 s after reaction initiation.The method demonstrated a good linear relationship within the boric acid concentration range of 0～9 mmol/L,with a detection limit of 0.34 mmol/L.The relative error of actual sample testing was less than 1%,indicating good accuracy and practical utility.Furthermore, a fully automated online detection system was built by integrating high-precision syringe pumps, multi-port valves, and an automated flow path system.This setup completed the entire calibration and sample detection process within 45 minutes without any pre-treatment steps, making it applicable for real-time monitoring and closed-loop control of boric acid concentration in industrial settings.