A UV-Visible spectrophotometer measures light intensity in the UV and visible spectrum after it passes through a sample.
The instrument's key components include:
Sources of Radiation
Radiation sources emit light, which interacts with the sample:
Deuterium Lamp: Emits UV radiation (190–380 nm) using deuterium gas. Provides a continuous UV spectrum, ideal for spectroscopy.
Tungsten/Halogen Lamp: Emits visible to near-infrared light (350–2500 nm). Tungsten filament ensures stability, halogen gas increases lamp life,
Wavelength Selectors
Monochromators isolate specific wavelengths from the light source:
Prisms: Disperse light based on refractive indices. Made of quartz/glass, they separate wavelengths effectively but are less common today.
Diffraction Gratings: Separate light by interference patterns. They offer high resolution, handle intense light, and are versatile, making them the most common in modern spectrometers.
Sample Cells (Cuvettes)
Hold the sample for measurement:
Materials:
Quartz: Transparent in UV and visible regions (190–800 nm).
Glass: For visible region measurements.
Plastic: Disposable; ideal for routine use but less precise.
Design: Rectangular with standardized path lengths (commonly 1 cm) for accurate quantitative measurements.
Maintenance: Clean thoroughly to prevent contamination. Handle quartz cuvettes carefully to avoid scratches.
Detectors (UV-Visible Spectrophotometer)
Convert transmitted light into measurable electrical signals:
Phototube: Releases electrons via the photoelectric effect to generate a current proportional to light intensity.
Photomultiplier Tube (PMT): Amplifies the signal using a series of dynodes, making it highly sensitive.
Photovoltaic Cell: Converts light into a direct current using semiconductor materials.
Silicon Photodiode: Converts light to current/voltage with high sensitivity and fast response, often used in reverse bias for enhanced performance.