Hanna Instruments PCA 300 Series - Manual (Page 13)

13
METHOD OF ANALYSIS
Free available Chlorine (monitored by the PCA300 series)
oxidizes the DPD indicator reagent at a pH between 5.5 and
6.0 to form a magenta-colored compound. The intensity of
the resulting color is proportional to the concentration of Chlo-
rine in the sample. The purpose of the buffer solution is to
maintain the proper pH.
To measure Total Residual Chlorine (Free available Chlorine
plus combined Chloramines) the PCA301 series adds Po-
tassium Iodide. The Chloramines in the sample cause
iodide ions to become iodine which then act with free Chlo-
rine to oxidize the DPD indicator. After the chemical reaction
is complete, the optical signal at 555 nm is compared to
the signal measured through the sample (before the re-
agents were added). From these measurements Chlorine
concentration is calculated.
Fluid Diagram of the Analyzers