The basic principle of IR spectroscopy relies on the “chemical fingerprints” that molecules leave when absorbing infrared radiation. Since they are unique to each compound, IR spectrometers can use these fingerprints to identify samples and perform quantitative analyses of complex substances.

To help you better understand the basic principle of IR spectroscopy, we’ve consulted our experts and explored its applications, instrumentation, and key components. We’ve also looked into used spectrometers and examined whether they can be a smart investment.

Keep reading to learn more about IR spectroscopy and its core principles.

What Is IR Spectroscopy?

Infrared (IR) spectroscopy is a technique that measures interactions between infrared light and matter to identify and quantify chemical compounds. Due to its accuracy, speed, and sensitivity, it is used across numerous disciplines, such as chemistry, environmental science, forensics, medical diagnostics, and astronomy.

IR spectroscopy is a fundamental method in modern chemical analysis, along with UV spectroscopy, mass spectroscopy, and Raman spectroscopy. All these techniques are used for analyzing and quantifying molecules, but their approaches are slightly different and sometimes complementary.

Furthermore, before delving deeper into the basic principle of IR spectroscopy, it is important to distinguish it from IR spectrometry.

IR spectroscopy, unlike IR spectrometry, refers to the theoretical understanding of how infrared light interacts with matter. In contrast, IR spectrometry focuses more on the instrumentation used for spectroscopic analysis, the IR spectrometer, and its design, operation, and maintenance.

What Is the Basic Principle of IR Spectroscopy?

The basic principle of IR spectroscopy relies on molecules’ ability to absorb infrared radiation with frequencies that match the vibrations of molecular bonds. This ability allows IR spectrometers to create a “chemical fingerprint” and identify all known compounds.

To help you understand the theory of IR spectroscopy, we will examine its key terms and concepts.

Molecular Vibrations and Bonds

Every molecule, regardless of its complexity and size, is composed of atoms held together by chemical bonds. However, these atoms aren’t fixed in place—due to their inherent energy, they move and vibrate in different ways.

Here are the two basic types of molecular vibrations:

• Stretching, which involves changes in the distance between two atoms and is further divided into symmetric and antisymmetric stretch
• Bending, during which the bond angle changes, resulting in four subtypes of molecular vibration—scissoring, rocking, twisting, or wagging

Each of these vibrations has its own frequency, unique to a specific chemical bond and compound. As a result, these frequencies function as a fingerprint; once they are detected, the molecule can be easily identified.

Absorption of Infrared Radiation

Infrared radiation, which is part of the electromagnetic spectrum invisible to the naked eye, travels in waves that can be detected and described. Although these waves have lower frequencies than visible light, they can match the frequencies of molecular vibrations and get absorbed by the molecule in question.

This absorption is the basic principle of IR spectroscopy, which can also be called vibrational spectroscopy due to its reliance on molecular vibrations.

Simply put, an IR spectrometer exposes a sample to a spectrum of infrared frequencies. Some simply pass through, while others are absorbed and disappear from the spectrum. Then, a detector placed behind the sample collects the data, determining which frequencies are missing from the original beam.

Afterward, the results are compared to spectral libraries and databases containing all known compounds and their interactions with infrared light. The computer can find a match and identify the sample in question within a few minutes.

Instrumentation of IR Spectroscopy

The instrumentation of IR spectroscopy includes four fundamental parts, which all play vital roles in analyzing and identifying the sample. While their specifics may differ between various models of spectrometers, their purpose and general operating principles remain the same.

The key components of IR spectrometers are the following:

• IR light source, which emits a broad spectrum of infrared light that passes through or gets absorbed by the sample. Most IR spectrometers use mid-infrared spectrum (MIR) with wavelengths of approximately 5 to 25 microns because this light coincides with molecular vibrations.
• Sample holder, where the sample interacts with infrared light. The sample holder must be chosen carefully to suit the specific requirements of the experiment and the sample’s state (gaseous, liquid, or solid).
• Detector, placed behind the sample, which captures the infrared radiation that passes through and converts the results into readable data on absorption.
• Data acquisition and analysis software, which collects, processes, and analyzes data received from the detector, creating graphs for qualitative and quantitative analysis. Modern software can also automatically compare the results to spectral databases and quickly identify the sample.

How Used IR Spectrometers Work

Used IR spectrometers work in the same way as new ones, as they also rely on the basic principles of IR spectroscopy. Essentially, the only difference is in their age and history of use.

For some lab owners, this difference is significant enough to cause concern—they often worry about used equipment’s quality and potential deficiencies. However, it’s important to note that most pre-owned lab instrumentation undergoes strict quality checks before it is launched on the market.

This is especially true when you’re buying from a trusted source, such as Surplus Solutions. Our affordable IR spectrometers are reliable, safe, and compliant with all relevant standardizations and requirements.

Applications of IR Spectroscopy in Labs

Applications of IR spectroscopy span numerous disciplines, including chemical analysis, food quality control, environmental monitoring, forensic science, medical diagnostics, materials science, and astronomy.

In the following sections, we will examine how IR spectroscopy is used in each of these fields in more detail.

#1. Chemical Analysis

The basic principle of IR spectroscopy is the molecular analysis and the identification of molecular structures, which is frequently applied in chemical labs.

However, aside from facilitating qualitative analyses, IR spectroscopy also yields precise quantitative results, accurately measuring the concentrations of specific components in a compound.

Namely, the higher the concentration of a component, the more effective it is at absorbing specific frequencies of IR radiation. So, if there are several components that absorb different IR frequencies, computer software can calculate their proportions in the sample based on the absorption rate.

#2. Food Quality Control

Spectroscopic analysis is used for quality control in the food industry, as it can inspect nutritional components, detect contaminants, and monitor changes during food processing. The IR spectrometer’s quantifying abilities are particularly important for verifying product labels and ensuring compliance with the Fair Packaging and Labeling Act (FPLA).

Furthermore, most food manufacturers opt for IR spectroscopy because it is a rapid and non-invasive quality control method. In other words, it leaves no trace on the food it analyzes and doesn’t affect its composition or contents.

#3. Environmental Monitoring

IR spectroscopy can detect and quantify greenhouse gases and various pollutants in air and water. As a result, it is frequently used to monitor the impact of human activity on the environment and provide information on potential areas of concern. That way, IR spectroscopy helps experts develop strategies that contribute to sustainability and environmental protection.

#4. Forensic Science

As a non-destructive technique, IR spectroscopy has numerous applications in forensic science, where it can analyze evidence without compromising it. It is used to identify both inorganic substances, such as paint, plastic, or ink, and organic matter, like hair, nails, or sweat.

Furthermore, IR spectroscopy can be leveraged to detect trace amounts of substances present at the crime scene, which can be vital for the progress of the investigation.

Finally, modern forensic IR spectrometers are portable and easy to carry to crime scenes and examine samples on the spot. This has been a revolutionary development in forensic science, as the risk of disturbing and compromising the evidence has dramatically dropped.

#5. Medical Diagnostics

IR spectrometers are used as non-invasive diagnostic instruments that analyze biological fluids and can detect the onset of various illnesses. They are particularly promising as cancer screening tools for rapid diagnosis through blood derivatives.

However, molecular abnormalities in the blood aren’t easy to detect, even with IR spectrometers. After all, blood plasma consists primarily of water, which can overshadow the critical components used in diagnostics and complicate the results.

Nevertheless, many medical researchers have high hopes for IR spectrometers in the future, expecting that the technology will develop further to account for potential problems.

#6. Astronomy

Infrared spectroscopy is used to observe and study the radiation in the universe that isn’t visible to the naked eye. All objects in space emit and absorb infrared light to a lesser or greater extent, and using telescopes that can detect it may provide fascinating information.

For instance, scientists can discover cool stars and nebulae or pierce through dense regions of dust and gases using infrared waves. As a result, most modern telescopes that study the universe are equipped with infrared spectrometers and detectors.

How to Choose the Right IR Spectroscope for Your Lab

To choose the right IR spectroscope for your lab, you need to consider your own needs and resources as well as the instrument’s specifications. You must also thoroughly research lab equipment suppliers to ensure that the device you’re buying is reliable and high-quality.

Here are a few factors you should consider when purchasing an IR spectrometer:

• Type of IR spectrometer. There are several kinds of IR spectrometers that perform similar functions but still have small differences worth taking into account. For instance, the Fourier Transform IR (FT-IR) spectrometer is more versatile, efficient, and accurate than the regular one. In contrast, the Attenuated Total Reflectance (ATR) spectrometer is ideal for analyzing complex samples, solids, and pastes.
• Wavelength range. As mentioned before, most spectrometers use mid-infrared light, which is usually sufficient for detecting and analyzing molecules. However, some spectrometers have broader ranges, encompassing near-infrared (NIR) radiation and far-infrared (Far-IR) light. This allows them to research matter that can’t be studied using MIR spectroscopy.
• Signal-to-noise ratio. A high signal-to-noise ratio (SNR) indicates high-quality, accurate results that aren’t skewed by background interference of any kind. Such results are easier to read and interpret, so it’s advisable to look into SNR before buying a specific spectrometer.
• Cost. New IR spectrometers can be pretty expensive, so it’s wise to determine how much you’d be willing to spend on one in advance. If your laboratory is on a tighter budget, consider buying a used IR spectrometer to avoid overspending.

Why Used IR Spectrometers Are a Great Choice

Used IR spectrometers are a great choice because they are accessible to most laboratories, even if they are small and can’t afford high-end equipment. Moreover, they reduce the need to produce new spectrometers, which, in turn, benefits the environment and contributes to sustainability.

Some lab owners may believe that a lower price tag indicates worse quality and hesitate to purchase any kind of used lab equipment. However, with a trusted vendor like Surplus Solutions, you don’t have to worry—as we guarantee the reliability and excellence of all our instruments.

Key Takeaways

While exploring the basic principle of IR spectroscopy, we’ve learned more about infrared radiation analysis and its ability to quantify and qualify various molecules. Thanks to that, IR spectrometers are used in numerous fields and can even detect phenomena in the universe invisible to the naked eye.

If you’re looking to buy reliable used spectroscopy equipment, Surplus Solutions has a wide range of affordable options. Browse through the selection on our website and keep an eye out for new arrivals!

What Is the Basic Principle of IR Spectroscopy FAQ