SENSITIVITY ENHANCEMENT OF FLUORESCENT PH INDICATORS BY INNER FILTER EFFECTS

Primary and secondary inner filter effects were employed to enhance the sensitivity of fluorescence measurements by using multiple indicator systems with complementary pH profiles. pH-sensitive absorbing indicators were mixed with pH-sensitive fluorescent indicators possessing complementary spectral overlap and pK(a)'s. The resulting solutions possessed greater fluorescence pH sensitivity. The pH changes were followed by monitoring the fluorescence emitted by one of the indicators. Different indicator systems were optimized with respect to indicator concentrations and excitation wave-lengths and provided increases in the DELTA-I/DELTA-pH slope by factors of 1.43-4.00.