Rapid and stabilization-free detection of chloride ion in silver chloride suspension using time-resolved scattering...

Chloride ion (Cl^-) detection is essential for environmental monitoring and industrial process control, yet conventional methods face limitations in stability, cost, or speed, especially in dynamic precipitation systems. To overcome these challenges, we report a novel time-resolved scattering spectroscopy-short-wavelength decrease & long-wavelength increase spectra (SDLI), observed during the formation of AgCl suspensions. With the passage of time, the extinction of light at short wavelengths exhibited a monotonic decrease, while the extinction at long-wavelength region displayed the increase. Notably, the sum of extinction at two equilibrium wavelengths where the decrease and increase rates were mathematically balanced provided a time-independent parameter correlated with Cl^- concentration, eliminating the need for suspension stabilization. This dual-wavelength strategy reduced detection time from >10 min to under 1 min with enhanced precision and achieved a detection limit of 0.013 mg/L. Mechanistic investigations suggested that the SDLI phenomenon arose from the wavelength-dependent differential responses of small-angle forward scattering light and transmitted light to increasing particle size, which ultimately led to opposite trends in extinction. The method was successfully applied to tap water and copper sulfate electroplating baths, demonstrating high precision, robustness, and suitability for rapid on-site analysis in complex matrices.