Which method is a colorimetric method for chloride determination?

• A. ISE
• B. Cotlove chloridometry
• C. Whitehorn titration
• D. Zall Color Reaction

Answer: (D)

Colorimetric chloride determination relies on forming a colored product whose intensity corresponds to the amount of chloride present. In the Zall Color Reaction, the chloride ions participate in a reaction that yields a chromophore, so the color intensity measured by a spectrophotometer (at a specific wavelength) is proportional to the chloride concentration. This direct link between color development and chloride amount makes it a true colorimetric method, suitable for rapid quantification in routine labs.

The other options do not fit the colorimetric approach. An ion-selective electrode measures chloride activity by a membrane potential (potentiometric method), not by a color change. Cotlove chloridometry and Whitehorn titration are titration-based techniques that determine chloride by endpoint reactions, not by producing and measuring a color change.