fluorescence Flashcards
What is fluorescence in drug analysis?
The emission of light by a molecule after it absorbs UV light, used to detect and quantify drugs in low doses.
How does fluorescence emission compare to absorption wavelength?
The emitted light wavelength is always longer (lower energy) than the absorbed light, known as the Stokes shift.
What is fluorimetry?
An analytical technique that measures the light emitted by molecules in a sample to analyze drug concentrations.
What are singlet and triplet states in fluorescence?
Singlet states have paired electron spins; triplet states have unpaired, parallel spins and longer lifetimes.
Describe the process of internal conversion in fluorescence.
A non-radiative energy loss where excited molecules transfer energy to the solvent, contributing to the Stokes shift.
explain the mirror image rule
the differences between vibrational levels are similar in the ground and excited states that the fluorescence spectrum resembles the first absorption band
explain the stokes shift
it is the gap between the max of the first absorption band and the max of fluorescence
What is inter-system crossing (ISC)?
A transition where the electron’s spin reverses, moving from a singlet to a triplet state, potentially leading to phosphorescence.
Why is a xenon lamp used in a spectrofluorimeter?
It provides high-intensity light needed for fluorescence, as fluorescence signals are typically weak.
What is quantum yield (ØF) in fluorescence?
It is a measure of fluorescence efficiency, representing the fraction of absorbed photons that result in fluorescence.
What are the main advantages of fluorimetry over UV/Vis absorbance?
Higher specificity, lower detection limits (up to 100 times lower), and ability to analyze very small drug quantities.
factors affecting fluorescence intensity
- source intensity
- fluorescence efficiency (quantum yield)
- concentration
- pathlength
- quenching
What is quenching in fluorescence?
A reduction in fluorescence intensity, often caused by high concentration (self-quenching) or other chemicals (chemical quenching).
How does chemical quenching occur?
By the removal of energy from an excited molecule via collision or complex formation with a quenching species.
What is the inner filter effect?
At high concentrations, much of the incident light is absorbed before reaching the center of the sample, leading to self-quenching.
