The titration reagent for the FIA titration using spectrophotometric
detection was prepared with NaOH concentration
of 5 × 10−5M NaOH, Septonex concentration of 3
× 10−3 M, and 0.1M KCl to adjust the ionic strength. The
thymol blue was used with the concentration of 4 × 10−3%:
the weighted amount was dissolved in the required amount
of 0.1MNaOH to receive the final (5 × 10−5 M) NaOH concentration.