Practice question

Fluorescence measurement counts emitted photons against essentially dark background, permitting detection down to picomolar concentrations using photomultipliers and photon counting. Glass pH electrode measures electrochemical potential with inherent drift and limited low-concentration response. Absorption spectrophotometry must discriminate small absorbance difference between intense incident and transmitted beams, restricting sensitivity to micromolar levels. Circular dichroism also detects small differential absorbance. Because quantum yield amplifies signal and background remains low, fluorescent probes track minute changes in ions, pH or metabolites with far superior sensitivity.