Partial Automation of Winkler Method by a Closed-Loop Flow System

Abstract

The entrapment of a water sample into a closed-loop system allows the direct determination of dissolved oxygen (DO) by the standard addition method. The samples are treated in the same way as for a normal Winkler determination but the final determination of DO is based on the measurement of triiodide at 456 nm. The sample passes repeatedly through the spectrophotometric detector by means of two peristaltic pumps and four valves. One of the valves is used to add the standard solution of KIO₃. Linear calibration curves are obtained with two additions. Although the method was initially intended for calibration of electrochemical probes, different water samples were analyzed by the proposed method.

Key Words:

• DO determination
• closed-loop
• FIA
• Winkler method