Detection of Tl(III) with luminol at physiological pH requires hydrogen peroxide as co-oxidant

► The reaction between Tl(III) (10-75 μM) and luminol at neutral pH requires H2O2. ► The reaction strongly depends on pH, with a maximal found at pH 7. ► Apparent affinity constant for Tl(III)-luminol complex was 1.95×1010 M−1. ► Superoxide anion was generated along the reaction. ► The two Tl(III) species found at neutral pH act through different mechanisms.