What Are the Different Types of Spectroscopy?

Of all the scientific techniques used to analyse matter, spectroscopy is one of the most useful. The highly specialised branch of science studies the way in which matter absorbs and emits light, with data used to scrutinise samples at the macro, molecular and atomic scale.

Building on the concept of using a prism to split white light into a rainbow of colours, spectroscopy scatters electromagnetic radiation into wavelengths to create a spectrum. Reactions are used to identify individual elements and gain insight into the unique characteristics of a sample.

The scope to investigate matter in such detail has made spectroscopy an important exploratory tool across a wide range of sectors and industries, from medical imaging and tissue analysis to astronomical research. This has led to the development of multiple spectroscopy types, usually characterised by the source of radiative energy used to smit light and trigger reactions.

Different spectroscopy types are suitable for different applications, with each technique offering its own unique pros and cons. Below, we take a closer look at the different spectroscopy types and how techniques are used for a staggering range of applications.   

X-Ray Spectroscopy

X-Ray Spectroscopy uses a beam of charged particles to excite atoms. This forces electrons to move to a higher energy level. As electrons return to their pre-excitation level, excess energy is emitted in the form of photons. X-ray spectrometers measure the wavelengths of these photons, with data used to identify and quantify elements.

Scientists can choose from two techniques – WDXS and EDXS. While slightly different, both techniques use radiation dispersion patterns to map atomic structure and identify elements.

• Wavelength-Dispersive X-Ray Spectroscopy (WDXS)

WDXS uses a crystal to diffract light and generate a single wavelength.

• Energy-Dispersive X-Ray Spectroscopy (EDXS)

EDXS uses a high-energy beam of charged particles to excite electrons and force them to emit radiation.

X-Ray Spectrometry is widely used for chemical analysis and is a valuable tool within the mining, geology, plastics and medical research sectors. X-Ray Spectrometry has also gained traction in the astronomy and astrophysics sectors, with sophisticated telescopes used to investigate phenomena like neutron stars and black holes. As a non-destructive analytical technique, X-Ray Spectrometry is popular with archaeologists, who use it to analyse the chemical composition of artifacts.

Flame Spectroscopy

Flame Spectroscopy measures the intensity of light emitted by matter when exposed to a flame. Wavelengths are used to identify elements, while the colour of the flame is used to calculate concentrations. Flame Spectroscopy is often used to identify alkali elements with low excitation states, including sodium, potassium and lithium.

Atomic Absorption Spectroscopy

Suitable for liquid and solid samples, Atomic Absorption Spectroscopy (AAS) uses a light source to generate electromagnetic radiation wavelengths. These wavelengths are used to detect elements, with absorption rates compared to benchmark data.

The water industry is one of the latest sectors to adopt AAS technology, with municipalities around the world using the technique to analyse samples and detect contaminants. Highly sensitive AAS spectrometers are capable of detecting extremely low concentrations of particles and contaminants, making the technique ideal for H20 analysis.

Spark Spectroscopy

Also known as Arc Atomic Emission Spectroscopy, this analytical technique is used to detect metallic elements in solid matter. Samples with no conductivity are blended with graphite powder to force reactions.

UV-Visible Spectroscopy

UV-Visible (UV/VIS) Spectroscopy measures the rate at which a chemical substance absorbs light. The quantitative technique does this by directing a UV or visible light source towards a sample and measuring the intensity of the beams that pass through. Absorption patterns are used to identify and quantify different chemical compounds.

UV-Visible Spectroscopy rose to recent challenges faced in the mRNA vaccine sector, which has struggled with issues like quality control and bacterial culture growth rates. UV/VIS was adopted as a solution to improve the quality of bacterial cultures, with a goal to minimise contamination and fast-track the production of mRNA vaccines.

UV-Visible Spectroscopy is also used to carry out important ibuprofen monograph tests in the US pharmaceuticals industry. Using a Thermo Scientific™ Evolution™ 260 Bio UV-Vis Spectrophotometer coupled with purpose-built software, teams are using the technique to ensure ibuprofen absorbance values fall within the acceptable range.

Near-Infrared Spectroscopy

Used for both quantitative and qualitative analysis, Near-Infrared (NIR) Spectroscopy is unique in that is operates in a specific region of the electromagnetic spectrum. The method analyses data within the 780 nm to 2500 nm range, i.e. the near-infrared region. NIRS is especially useful in the food and beverage sector, where it’s used to analyse the fat, protein, starch and moisture contents of products. NIR Spectroscopy is also a mainstay in the pharmaceuticals sector, with the technique used to monitor moisture levels in freeze-dried drug products.

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) Spectroscopy relies on specialised equipment to map the molecular structure of matter at the atomic level. The advanced technique is also used to determine solubility, phase changes and predict diffusion potential. A magnetic field is used to excite an atomic nucleus and force it to emit radio frequency pulses. These pulses are used to determine the resonant frequency of the nucleus and ultimately, detect chemical elements.

Fourier Transform Infrared Spectroscopy

Fourier Transform Infrared (FTIR) Spectroscopy uses absorption, emission and photoconductivity rates to collect high-resolution data for liquids, solids and gases. The technique operates in a wide spectral range, giving it a unique advantage over other methods such as Dispersive Spectroscopy. Results are fast and reliable, making FTIR Spectroscopy suitable for a wide range of applications. It’s especially useful for identifying unknown materials, making it a gold-class technique for screening processes.

FTIR is a workhorse in the pharmaceuticals industry, where products must comply with strict regulatory requirements. High sensitivity and a wide spectral range make FTIR Spectroscopy a valuable tool for product development, testing and quality control.

In the polymers and plastics industry, FTIR Spectroscopy is used to identify compounds such as rubbers, resins and adhesives. From initial design and product development to molecular degradation assessment and failure analysis, the technique is used extensively across the sector.

Raman Spectroscopy

Raman Spectroscopy is one of the latest techniques to make waves in the scientific realm. The technique uses electromagnetic radiation to chart the chemical composition of matter and has the capacity to simultaneously measure multiple variables. Not only is Raman Spectroscopy highly accurate but it offers real-time results.

Over the past decade, it’s emerged as a valuable tool used to analyse geological materials. Applications for Raman Spectroscopy extend far beyond mining and hydrocarbon exploration, with experts maintaining the analytical technique can be used to predict natural disasters such as volcanic explosions and earthquakes, chart climatic changes and manage water resources.

“Raman spectroscopy is an established analytical technique for the analysis of geological samples. It not only provides a fast and efficient way of identifying specific materials but also considerable information on molecular structure and chemical environments,” reads a report written by Dr. Robert Heintz, an inhouse expert at Thermo Fisher Scientific.

Mid-Infrared (MIR) Spectroscopy 

The booming medical cannabis industry has recently adopted Mid-Infrared (MIR) Spectroscopy as an accurate and affordable form of Process Analytical Technology (PAT). A study published in the peer-reviewed journal Spectrochimica Acta Part A explored the benefits of MIR Spectroscopy for quantifying phytocannabinoids such as CBD and THC.

“The complexity of the sample (plant tissue or plant extract), the variability of the samples regarding their origin and horticultural maturity, as well as the non-uniformity of the plant material and the flower-ATR crystal contact (in the case of Cannabis flowers) were governing the accuracy descriptors,” reads the abstract. “Taking into account the presented results, ATR-MIR should be considered as a promising PAT tool for THC and CBD content estimation, in terms of critical material and quality parameters for Cannabis flowers and extracts.”

Spectroscopy vs Spectrometry

While Spectroscopy vs Spectrometry sound similar, it’s important to understand the difference between the two terms.

Spectroscopy is the study of how matter interacts with radiated energy, such as an electromagnetic light source. It’s a theoretical term used to describe the absorption characteristics and behaviours of a sample. Spectra produced by matter is analysed and used to gain insight into its unique physical and chemical properties.

In comparison, spectrometry is a practical application uses to collect quantitative and qualitative data. Interactions between light and matter are measured using specialised instruments that focus on a specific spectrum.

To summarise, spectroscopy describes the theoretical science of studying interactions between matter and radiated energy, while spectrometry is a practical application used to gain detailed insight into the unique characteristics of matter.

Diving deeper into the realm of spectroscopy

The techniques listed above are just some of the different spectroscopy types used to analyse matter at the macro, molecular and atomic scale. Reflectance Spectroscopy is one of the latest players to storm onto the scene, with the non-destructive, quantitative technique adopted by a myriad of industries, from biospecimen analysis to food quality control. Writing on behalf of Ocean Insight Inc, Rob Morris dives into the technique in more detail in ‘Reflectance Spectroscopy - A Useful Technique for Analysing Solid Samples’.