The principle of UV-Vis spectroscopy is the interaction between ultraviolet/visible light and matter, resulting in the absorption of specific wavelengths. Since different molecules absorb different wavelengths, this technique can be used to identify and quantify components in a sample.

To better understand the underlying principle of UV-Vis spectroscopy, we’ve asked our experts about its instrumentation, applications, and importance in various disciplines.

In this article, we will share what they’ve told us about ultraviolet/visible spectroscopy.

What Is UV-Vis Spectroscopy and Why Is It Important?

UV-Vis spectroscopy is a technique that uses light in the ultraviolet and visible range of the electromagnetic spectrum to identify and quantify molecules in a sample. This type of spectroscopic analysis has numerous applications, particularly in chemistry, pharmacy, environmental science, and the food and beverage industry.

The core principle of UV-Vis spectroscopy is the interaction between ultraviolet/visible light and molecules called chromophores. However, before we delve into the specifics, we should quickly overview these key concepts.

The ultraviolet/visible light is part of the electromagnetic spectrum with wavelengths between 190 nm and 800 nm. More specifically, the ultraviolet region is in the 190–400 nm range, while visible light, with its seven colors, is located in the 400–800 nm range.

Although ultraviolet and visible light have different properties, they are classified together because they have similar effects on chromophores—molecules that absorb light of specific wavelengths in the UV-Vis range.

However, we will discuss these effects in the following section.

What Is the Basic Principle of UV-Vis Spectroscopy?

The basic principle of UV-visible spectroscopy is electrons’ ability to absorb specific wavelengths of light and move to a higher energy state. By measuring the intensity of light that passes through a sample, UV-Vis spectrometers can identify molecules and determine their concentrations.

In the following sections, we will examine the theory of UV-Vis spectroscopy in greater detail.

Electronic Transitions and Absorption

An atom has a simple structure—a nucleus composed of protons and neutrons, and electrons inhabiting orbitals around it. Under normal circumstances, electrons are arranged in the ground-state configuration, representing each electron’s lowest energy level.

However, when an electron absorbs energy (i.e., a photon of light), it becomes excited and moves to a higher-energy orbital. This is called an electronic transition, and it occurs when light from the UV or visible spectrum hits chromophores.

To transition into a higher state, an electron must absorb a specific amount of energy uniquely determined by the protons and neutrons in the nucleus. So, when the light from a UV-Vis spectrometer reaches the sample, only the wavelengths with the required energy will reduce in intensity or disappear from the spectrum.

Based on the absorbed wavelength, analytical software can identify the element or compound in question by comparing it to the existing database.

Factors Affecting Light Absorption

According to the Beer-Lambert law, two main factors affect light absorption as it passes through a sample—the sample’s concentration and the path length of the absorbing medium.

As mentioned before, if we have several molecules in a sample, each will absorb a different wavelength of the UV-Vis light spectrum. However, the rate of absorption isn’t exactly the same, either.

Essentially, the higher the molecule’s concentration and the longer the path the light must travel through the sample, the greater the absorbance. This is evident from the decreased intensity of light that reaches the detector.

With the application of the Beer-Lambert law, it is possible to calculate concentrations of specific molecules in a solution. As a result, UV-Vis spectroscopy can be used for quantitative research as well as qualitative analysis.

Instrumentation of UV-Vis Spectroscopy

The instrumentation of UV-Vis spectroscopy consists of four components that enable light absorption measurement and assist in data analysis and interpretation.

Here are the basic parts of a typical UV-Vis spectrometer:

• Light source, which emits a range of wavelengths in the UV-Vis spectrum. Xenon lamps are commonly used for this purpose, but their instability makes them unreliable. Hence, they are often replaced by deuterium lamps for UV light and halogen or tungsten lamps for visible light.
• Wavelength selector, which narrows down the broad range of wavelengths in a light beam to the few necessary for the experiment. Typically, UV-Vis spectrometers use monochromators containing a prism as wavelength selectors, though different kinds of filters can play the same role.
• Sample container, which holds the sample in single-beam spectrometers or the sample and the reference in double-beam spectrometers. The latter splits the light from the source into two beams; one passes through the blank sample, and the other hits the actual sample. Then, the results can be compared, and the absorbance rate can be easily calculated.
• Detector, which converts the passing light into electric signals that can be read and interpreted by appropriate computer software. The information obtained from the detector is usually presented as a graph, where the peak represents the wavelength at which the absorbance rate is the highest.

5 Applications of UV-Vis Spectroscopy in Labs

Common applications of UV-Vis spectroscopy include pharmaceutical analysis, food and beverage quality control, environmental monitoring, chemical research, and DNA and RNA analysis.

Below, we will examine all these uses in more detail.

#1. Pharmaceutical Analysis

Pharmaceutical research uses the principles of UV-Vis spectroscopy to discover and develop drugs, quantify impurities, and identify chemical components. In other words, it can serve as an effective quality control method, especially because it has a minimal effect on the drug samples it is inspecting.

#2. Food and Beverage Quality Control

Thanks to its ability to perform quantitative analyses in labs, UV-Vis spectroscopy is crucial for measuring the concentrations of ingredients in food and beverages.

For instance, the caffeine content in coffee and tea cannot exceed a specific legal limit, so UV-Vis spectrometers are used to quantify it and ensure it’s accurately represented on labels. Similar tests can be performed on other types of food and beverages to check whether they comply with the Fair Packaging and Labeling Act (FPLA).

#3. Environmental Monitoring

Environmental sciences frequently use UV-Vis spectrometers to analyze air, soil, and water content and detect potential contaminants. This is essential for identifying and preventing public health threats, as well as developing strategies for improved sustainability.

#4. Chemical Research

Chemistry uses the principles of UV-visible spectroscopy to analyze solids and solutions, identify their components, and measure each compound’s concentration. Furthermore, UV-Vis spectroscopy can provide information on molecular and electronic structures of organic and inorganic substances, which is very beneficial for research.

#5. DNA and RNA Analysis

In genetics, the principles of UV-Vis spectroscopy are applied to quickly verify the purity and measure the concentrations of DNA and RNA samples. This is particularly important when preparing DNA for sequencing—the sample must be contamination-free, which can be determined using a spectrometer.

How to Choose the Right UV-Vis Spectroscope for Your Lab

To choose the right UV-Vis spectroscope for your lab, carefully research the available features and consider your needs. Though UV-Vis spectrometers all have the same purposes and similar designs, some specifications may differ, and these are important to take into account.

Here is what you should keep in mind when buying a UV-Vis spectrometer:

• Single-beam vs. double-beam. As mentioned before, there are two types of UV-Vis spectrometers—single and double-beam. The former measures the differences in absorption before and after placing the sample, while the latter, using two beams, instantly compares the absorption rate between the sample and reference.
• Sensitivity. The more sensitive a UV-Vis spectrometer is, the more nuanced its results will be. This is particularly important when working with complex samples comprising many components whose concentrations may be low and, therefore, difficult to detect.
• Specific features. Some UV-Vis spectrometers use all-purpose xenon lamps as a light source, while others prefer a combination of deuterium and halogen or tungsten. Similarly, sample holders may be cuvettes, cell containers, and microplates, depending on the sample type. Compare the benefits and disadvantages of various options to decide what would suit your needs.
• Cost. UV-Vis spectrometers can cost between $3,000 and $60,000, depending on the model and type. These prices may exceed a small laboratory’s budget, especially if the goal is to buy a high-end instrument. In that case, it’s advisable to look into used lab equipment vendors, which can offer excellent deals for high-quality spectrometers.

Why Used UV-Vis Spectrometers Are the Right Choice

Although used UV-Vis spectrometers for labs are far more accessible than new systems, many lab owners hesitate to buy them, worried about potential deficiencies. These concerns stem from the idea that lab instrumentation’s quality declines with age due to daily wear and tear.

However, as a reliable vendor of used lab equipment, Surplus Solutions ensures this is not the case by subjecting its instruments to strict quality checks. Only those that meet the highest criteria receive a quality assurance certificate and can be launched on the market.

As a result, you can purchase a high-quality used UV-Vis spectrometer that meets all manufacturer specifications at a fraction of the new instrument’s cost. This allows you to redirect some of the leftover funds to buy other equipment or conduct relevant research instead of spending too much on a spectrometer.

Key Takeaways

While reviewing the underlying principle of UV-Vis spectroscopy, we’ve learned about this technique’s numerous applications in various fields. Generally speaking, UV-Vis spectrometers are used for qualitative and quantitative analysis in a range of disciplines, including pharmacy, environmental science, chemistry, medicine, and more.

However, complex as they are, UV-Vis spectrometers aren’t very affordable, so smaller laboratories may find new systems inaccessible.

Luckily, pre-owned lab equipment vendors, such as Surplus Solutions, offer high-quality alternatives at a fraction of the price. Besides UV-Vis spectrometers, you can find other kinds of affordable lab instrumentation, all in pristine condition.

So, visit our website often and keep an eye out for new arrivals!

What Is the Principle of UV-Vis Spectroscopy FAQ