instrumentation (analytical spectroscopy) Flashcards
What are the main components of a spectrophotometer?
Light source, monochromator, sample area, and detector.
What are the two types of light sources commonly used in spectrophotometry?
Tungsten lamp (for visible light, 350-2000 nm) and deuterium lamp (for UV light, 200-370 nm).
Tungsten lamp (for visible light, 350-2000 nm) and deuterium lamp (for UV light, 200-370 nm).
It splits a polychromatic beam into its component wavelengths by moving the dispersing element or exit slit.
What are the two main types of detectors used in spectrophotometers?
Photomultiplier tube (PMT) and photodiode array detector.
How does a photomultiplier tube (PMT) detector work?
It amplifies electrons through a series of dynodes, producing a measurable current from a few photons.
What is the difference between single beam and double beam spectrophotometers?
Single beam measures one path of light, while double beam compares light intensities in sample and reference paths for more accurate readings.
Why are tungsten and deuterium lamps used as light sources in spectroscopy?
They cover the visible and UV ranges, which are important for various analytical measurements.
What is UV/Vis absorption spectroscopy used for in drug analysis?
To quantify drugs, determine drug properties (e.g., pKa, solubility), monitor degradation, and as an identity check.
What three processes decrease the intensity of light in UV/Vis spectroscopy?
Reflection at phase boundaries, scattering from non-homogeneity, and absorbance by atoms or molecules.
What is λ max?
The wavelength at which maximum absorbance occurs, often used for optimal sensitivity in drug analysis.
Define Beer’s and Lambert’s Laws in spectrophotometry.
Beer’s Law relates absorbance to concentration, while Lambert’s Law relates absorbance to path length. Combined, they form the Beer-Lambert equation: A = εcl.
What is molar absorptivity (ε) in the Beer-Lambert law?
A constant representing the absorbance of a 1 M solution in a 1 cm cell, with units of L mol⁻¹ cm⁻¹.
What are common deviations from Beer’s Law?
High concentration effects, stray light, refractive index changes, and pH variations.
How does pH affect the absorption spectrum of a drug?
Changes in pH can alter the λ max due to shifts in the ionization state of chromophores, resulting in bathochromic (red) or hypsochromic (blue) shifts.
What is a bathochromic shift?
A shift of λ max to a longer wavelength, also known as a red shift, often caused by the presence of auxochromes like NH₂, OH, and SH groups.
