<p>A quantitative analysis method (QAM) that separates the extinction contributions of dispersed phases and organic pollutants in laboratory-prepared solid–liquid dispersions (LSDs) through mathematical methods is a critical component of automated spectrophotometric monitoring systems (ASMSs). However, existing research primarily focuses on local intensity and linear characteristics of the dispersed phase's extinction spectra, often neglecting the significant impact of local curvature features on quantitative accuracy. To address this limitation, we propose a novel method called Local Curvature Correction (LCC), which improves quantitative accuracy by incorporating the local curvature of the dispersed phase's extinction spectrum. The LCC method involves three steps: (1) identifying a target wavelength corresponding to the maximum absorption of organic pollutants and selecting two reference wavelengths with only the dispersed phase's extinction contribution; (2) utilizing the linear relationship between the reciprocal of extinction and wavelength at these three wavelengths to calculate the dispersed phase's extinction at the target wavelength; and (3) applying the additivity law to determine the absorbance of organic pollutants. The LCC method was validated through adsorption equilibrium and photocatalytic degradation experiments involving various dispersed phases (activated carbon, graphitic carbon nitride, or nano-TiO₂) and organic pollutants (phenol, Acid Orange 7, or rhodamine B). The results were compared with traditional methods such as dual-wavelength, triple-wavelength, and derivative spectroscopy. Comparative results demonstrated that the LCC method achieves significantly higher quantitative accuracy than the three traditional methods. This study provides a more broadly applicable and accurate QAM for ASMSs, thereby enhancing their effectiveness in evaluating the adsorption and photocatalytic performance of powder materials through LSDs.</p>