Simultaneous Quantification of Dispersant Adsorption and Pesticide Solubilization by UV –Vis Spectrophotometry Combined With Chemometrics

ABSTRACT In pesticide suspension concentrate formulations, interfacial adsorption of dispersants onto active‐ingredient particles and solubilization of pesticide molecules by dispersant micelles frequently coexist; however, analytical methods capable of simultaneously characterizing these interfacial and bulk‐phase processes remain limited. Herein, a multivariate calibration strategy combining ultraviolet–visible (UV–Vis) spectrophotometry with partial least squares (PLS) regression and competitive adaptive reweighted sampling (CARS) was developed. The method enabled simultaneous determination of residual tristyrylphenol ethoxylates (TSPEO) and prometryn in processed supernatants, allowing TSPEO adsorption to be quantified indirectly by mass balance. In the hold‐out validation set, the CARS model incorporating single‐component (SC) spectra achieved coefficients of determination for validation ( R 2 val ) of 0.9965 and 0.9904 and root mean square errors of prediction (RMSEP) of 6.1471 and 1.0129 mg/L for TSPEO and prometryn, respectively. Prometryn predictions also showed good agreement with high‐performance liquid chromatography (HPLC) measurements. Application of the method showed that wet milling increased the Langmuir‐derived apparent maximum adsorption capacity of TSPEO from 4.02 to 13.18 mg/g, whereas the nonmilled system exhibited linear micellar solubilization of prometryn above the critical micelle concentration (CMC), with a weight solubilization ratio (WSR) of 0.0291 g/g. These results provide a quantitative framework for investigating coupled dispersant adsorption and pesticide solubilization in suspension concentrate systems.