Which statement about fluorometry is true?

Which statement about fluorometry is true?

• A. Fluorescence is an inherently more sensitive technique than absorption.
• B. Emission wavelengths are always set at lower wavelengths than excitation.
• C. The detector is always placed at right angles to the excitation beam.
• D. All compounds undergo fluorescence.

Answer: (A)

In fluorometry, the signal comes from light emitted by the molecule after it has absorbed energy, and that emitted light can be detected with very low background. Because you can isolate a specific emission band and filter out the excitation light, the measurement often achieves a higher signal-to-noise ratio than direct absorption measurements. This makes fluorescence measurements inherently more sensitive in many practical cases, especially when the fluorophore has a good quantum yield and the background is low. Regarding the other statements, emission generally occurs at longer wavelengths than the excitation—there’s a Stokes shift, not a shorter one—so the idea that emission is always at lower wavelengths is incorrect. The detector geometry in fluorimeters is commonly set up to minimize stray excitation light, often at right angles, but that arrangement isn’t a universal requirement for all instruments. Lastly, not all compounds fluoresce; only those with appropriate electronic structure and sufficient quantum yield produce detectable fluorescence.

In fluorometry, the signal comes from light emitted by the molecule after it has absorbed energy, and that emitted light can be detected with very low background. Because you can isolate a specific emission band and filter out the excitation light, the measurement often achieves a higher signal-to-noise ratio than direct absorption measurements. This makes fluorescence measurements inherently more sensitive in many practical cases, especially when the fluorophore has a good quantum yield and the background is low.

Regarding the other statements, emission generally occurs at longer wavelengths than the excitation—there’s a Stokes shift, not a shorter one—so the idea that emission is always at lower wavelengths is incorrect. The detector geometry in fluorimeters is commonly set up to minimize stray excitation light, often at right angles, but that arrangement isn’t a universal requirement for all instruments. Lastly, not all compounds fluoresce; only those with appropriate electronic structure and sufficient quantum yield produce detectable fluorescence.