In the ultraviolet-visible spectrum, UV-Vis spectroscopy, also known as ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometer (UV-Vis), is often referred to as reflectance spectroscopy or absorption spectroscopy.
What is UV-Vis Spectroscopy
In the ultraviolet-visible spectrum, UV-Vis spectroscopy, also known as ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometer (UV-Vis), is often referred to as reflectance spectroscopy or absorption spectroscopy.
It is also known as electron spectroscopy because of the electron transition that occurs. It is a straightforward, affordable, adaptable, and non-destructive method that permits the sample to be utilized once more for additional examination. Using the Beer-Lambert law, this qualitative, quantitative, and analytical method determines how much distinct ultraviolet and visible light is absorbed or transmitted through a given material by comparing it to a blank or reference sample. It conducts research in a vacuum.
Types of UV-Vis Spectrophotometers
UV-Vis spectrophotometers can be categorized based on their optical design and operation.
- Single-Beam Spectrophotometer
Measures the light intensity before and after passing through the sample sequentially.
Less expensive but susceptible to drift and less accurate over time.
- Double-Beam Spectrophotometer
The light is split in two, with one path going through the sample and the other going through a reference cuvette.
More stable and accurate; used in research and industrial laboratories.
- Diode Array Spectrophotometer
Uses a fixed diffraction grating and an array of photodiodes to collect an entire spectrum at once.
Main Components of a UV-Vis Spectrophotometer
A typical UV-Vis spectrophotometer includes several critical components:
- Light Source
The light source must be stable and cover a broad range of wavelengths.
Deuterium lamp: Gives off UV light all the time, from about 190 to 400 nm.
Tungsten-halogen lamp: Encompasses the visible spectrum between around 350 to 2500 nm.
Many instruments use both lamps to span the entire UV-Vis range, switching between them depending on the selected wavelength.
- Monochromator
The monochromator isolates specific wavelengths of light from the broad spectrum emitted by the light source.
Prisms or diffraction gratings are used to disperse the light into its component wavelengths.
Slits control the bandwidth and direct the chosen wavelength through the sample.
- Sample Holder
Samples are typically held in transparent cuvettes made of materials that do not absorb in the UV-Vis range.
Quartz cuvettes: Used for UV measurements (glass absorbs UV light).
Glass or plastic cuvettes: Used for visible-light measurements.
- Detector
Before reaching the detector, the light passes through the sample. The transmitted light’s intensity is measured by the detector, which then transforms it into an electrical signal.
Photodiode: Used for rapid and precise measurements.
Photomultiplier tube (PMT): Highly sensitive, ideal for detecting very low light levels.
Charge-coupled devices (CCDs): Used in modern diode array spectrometers to capture full spectra simultaneously.
- Data Processor and Display
The electrical signals from the detector are sent to a data processor, where they are converted into absorbance or transmittance values.
A graph of absorbance vs. wavelength (an absorption spectrum) is generated.
Software is used to analyze, compare, and quantify sample data.
UV-Vis Spectroscopy Principle
A molecule becomes energized when it is exposed to a particular wavelength of light. After being stimulated, the electron transitions from the ground (lower) energy state to the higher energy level. Since electrons in lower energy orbitals spend energy to rise to higher energy levels, when an electron jumps off, it absorbs light energy.
Energy cannot be generated or destroyed, but it can change forms. Because matter’s energy levels are quantized, only light with the exact amount of energy that can trigger transitions from one level to another will absorb when it passes through the EMR (UV-Vis range of 200-800 nm).
The intensity of the light perceived is lost if the energy is used. The energy difference between the two energy levels will now be equal to the energy absorbed by the electrons.
An electron transition takes place during this phase. Therefore, the spectra that are obtained following the interaction of electromagnetic radiation are referred to as absorption spectra. Thus, the term “electron spectroscopy.” Similarly, the spectra that are obtained when electrons from a higher energy level move to the ground energy level are referred to as emissions.
By applying the Beer-Lambert rule to the absorption of spectra generated by various samples at particular wavelengths, the concentration of the sample can be directly ascertained.
With the correct add-ons and software, you can easily increase the capabilities of your UV-Vis and Vis spectrophotometers. Upgrade your instrument hardware with a variety of accessories for temperature control units, sipper systems, fiber optic probes, interface cables, replacement bulbs, standards, and holders for single and multiple cells. Higher resolution spectrum scans, peak pick, scan overlay, kinetics, automated process computations, performance checks, and regulatory compliance can all be enabled with extra software. Decide which combinations best meet your needs.
