Optical response of Film-6, [A], and Film-7, [B], towards various anions as measured in 100 mM β-alanine-phosphate buffer, 1 mM CDTA, pH 3.6: (●) fluoride, (■) thiocyanate, (△) perchlorate, (▼) nitrate ~ nitrite, and (○) bromide ~ chloride ~ sulfates. Solid lines are the theoretical response curves of the fluoride optical sensing film toward various anions calculated using eq. 2. Absorbance values at 537 nm were employed to calculate α values