What is NIR spectroscopy?

Jan 8, 2024

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This article is Part 1 of a series.

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Near-infrared spectroscopy, also known as NIR spectroscopy or NIRS, has been an established analytical technique for more than 30 years. It is a fast and reliable method to measure chemical and physical properties in solids and liquids. This first part of the series about near-infrared spectroscopy gives an introduction to how it works and presents the advantages and versatility of the technique.

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How does NIR spectroscopy work?
Measuring methods for solid and liquid samples
Advantages of NIR spectroscopy
NIR spectroscopy applications

How does NIR spectroscopy work?

NIR spectroscopy analyzes the interaction between light and matter to generate a spectrum. In spectroscopic methods, light is typically not described by the applied energy, but by the wavelength. NIR spectroscopy operates in the near-infrared region of the electromagnetic spectrum, i.e., in the wavelength range of 780 to 2500 nm. In other words, a NIR spectrometer measures the absorption of light from the sample at different wavelengths in the NIR region. It must be noted that near-infrared is a different wavelength range than mid-infrared. The difference between these two techniques is explained in the blog article «NIR vs. IR: What is the difference?».

NIRS is a secondary technique. This means a prediction model needs to be created first. You can compare this, for example, to HPLC. If you want to identify or quantify a substance with HPLC, first you need to prepare standard solutions of the substance and measure them to create a calibration curve.

This is similar with NIRS: first you need to measure a number of spectra with known concentrations or known parameter values that were gathered from a primary method such as titration. A prediction model is created out of these spectra using chemometric software (e.g., the Metrohm OMNIS software). Then, routine analysis of unknown samples can start. We explain in more detail how prediction models are created in the blog article «How to implement NIR spectroscopy in your laboratory workflow».

NIR spectroscopy is especially sensitive to the presence of certain functional groups including -CH, -NH, -OH, and -SH. Therefore, it is an ideal method to quantify chemical parameters such as water content (moisture), hydroxyl value, acid number, and amine content, just to name a few.

In addition, the interaction between light and matter is also dependent upon the matrix of the sample itself, which allows the detection of physical and rheological parameters such as particle sizing, density, intrinsic viscosity, and melt flow rate.

Measuring methods for solid and liquid samples

To understand the benefits of NIR technology, it is important to start by understanding how we measure NIR spectra. NIR spectroscopy enables the analysis of different types of samples. Depending on the sample type, researchers require different instruments.

Several measurement methods are available for samples ranging from clear liquids to opaque pastes and powders. Choosing the right measurement method, sampling module, and accessories is the most important step to developing robust NIR methods. Below, we show the different methods for various sample types (diffuse reflection, transflection, and transmission).

Measuring method for solid samples

Diffuse reflection: Cream, paste, granulates, coarse and fine powders

Example for measuring a solid sample

Measuring methods for liquid samples

Transflection: Liquids and gels

Transmission: Liquids

Example for measuring a liquid sample

Advantages of NIR spectroscopy

The procedure for obtaining the NIR spectrum already indicates two main advantages of near-infrared spectroscopy: simplicity regarding sample measurement and speed. These and other advantages of NIR analyses are listed here:

Fast technique – results in less than 1 minute.
No sample preparation required – solids and liquids can be used in pure form.
Low cost per sample – no chemicals or solvents needed.
Environmentally-friendly technique – no waste generated.
Non-destructive – precious samples can be reused after analysis.
Easy to operate – inexperienced users are immediately successful.

NIR spectroscopy applications

NIRS is a versatile technique and can be used for various applications, both for the analysis of chemical and physical parameters. NIR analysis is implemented in the chemical, polyol, polymer, food and beverage, animal feed, pharma, pulp and paper, paint, petrochemical, biofuel, personal care, textile, and semiconductor industries. Typically, NIR instruments are used for quality assurance and quality control, raw material identification or verification of chemical composition, process control and real-time reaction monitoring, and screening.

You can also browse our Application Finder for NIR spectroscopy applications:

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Near-infrared spectroscopy is a reliable method to measure chemical and physical properties in solids and liquids. This fast method can also be successfully implemented to be used by staff without any laboratory education for routine analysis.

Now that you know what NIR spectroscopy is, learn how it can be easily implemented into your laboratory workflow:

How to implement NIR spectroscopy in your laboratory workflow

Your knowledge take-aways

Learn more about our NIR spectrometers for lab and process analysis, as well as Raman solutions

What is NIR spectroscopy?

How does NIR spectroscopy work?