The effect of pH on the transport process can also be studied using the lucigenin assay, as the fluorescence of lucigenin and KSV(Cl -) remain approximately unchanged in a range of pH 4-10 (see Figures ). Considering the KSV for OH -, the fluorescence of lucigenin would start to decrease significantly at hydroxide concentrations higher than 0.1 mM (pH >10) and the sensitivity towards to Cl -would be lower because of fluorescence quenching by hydroxide (see Figure ). Thus, anionophoric activity can be studied conveniently by the lucigenin assay at pH 4-9. 4.4 Cl -/HCO 3 -antiport