PARTIAL AUTOMATION OF WINKLER METHOD BY A CLOSED-LOOP FLOW SYSTEM

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 Winkl er determination but the final determination of DO is based on the mea surement 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. Alth ough the method was initially intended for calibration of electrochemi cal probes, different water samples were analyzed by the proposed meth od.