spectrometry instrumentation Flashcards
What are the key components of a spectrophotometer?
Light source, dispersion device, sample area, and detectors.
What are the common light sources used in spectrophotometers and their purpose?
Tungsten lamps (350-2000 nm) for colorimetry and deuterium lamps (200-370 nm) for UV spectroscopy.
What is the function of a monochromator in a spectrophotometer?
It isolates a single wavelength of light from a broad spectrum for precise measurements.
What are the two types of monochromators commonly used?
Prisms and diffraction gratings.
How does a diffraction grating work in a spectrophotometer?
It splits the incoming polychromatic radiation into its component wavelengths by dispersing it at an angle.
How does a photomultiplier tube (PMT) work as a detector?
It amplifies a small number of photons into a measurable current by using an array of dynodes with increasing positive voltage.
What is a photodiode array detector, and what is its advantage?
It consists of an array of photodiodes on a silicon crystal, measuring the whole spectrum simultaneously, ideal for rapid UV/Vis measurements.
What is the main difference between single beam and double beam spectrophotometers?
Single beam measures the intensity of light before and after passing through the sample separately, while double beam compares the light intensity simultaneously between a reference and sample path.
What qualities are ideal in a light source for spectrophotometry?
A constant intensity, low noise, and long-term stability.
What are some uses of UV/Vis absorption spectroscopy in drug analysis?
Quantifying drugs in formulations, determining pKa, measuring partition coefficients and solubilities, monitoring drug release in dissolution testing, and checking drug identity.
What three processes decrease the intensity of polychromatic light passing through a sample?
Reflection at phase boundaries, scattering by non-homogeneous samples, and absorbance by atoms or molecules in the solution.
Why is the wavelength of maximum absorption (λmax) used in spectrophotometry?
It provides the greatest sensitivity and reduces interference from small variations in wavelength.
