Why is fluorometry considered a better technique than spectrophotometry?

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Fluorometry is valued over spectrophotometry primarily because it yields much higher sensitivity and greater specificity. When a fluorophore is excited, it emits light at a different wavelength, and this emission can be measured with very little interference from the sample matrix. Most substances in a typical sample do not fluoresce, so the background signal is very small, which dramatically improves the signal-to-noise ratio. Additionally, the ability to select specific excitation and emission wavelengths acts like a orthogonal filter, helping to distinguish the analyte from other components that might absorb light but do not emit fluorescence. This combination means you can detect much lower concentrations and with fewer interferences than with simple absorbance measurements.

The idea that fluorometry is simply faster or that it needs no calibration or is immune to drift isn’t generally correct. Calibration is still necessary, and while many fluorometric assays can be rapid, speed isn’t the defining advantage. Instrument drift can occur in either technique, and the notable strengths of fluorometry lie in its sensitivity and selectivity due to fluorescence detection.