NIR vs IR: What is the difference?

In the first article in our series about near-infrared (NIR) spectroscopy, we have explained what NIR spectroscopy is. This article focuses on the difference between near-infrared and infrared (IR) spectroscopy, which is often also called mid-infrared (mid-IR) spectroscopy. We will also discuss why NIR spectroscopy might be more suitable than IR spectroscopy for your analytical challenges in the laboratory and in industrial manufacturing processes.

Differences in wavelengths and energy

We have defined NIR spectroscopy as the analysis of the interaction between NIR light and matter. In spectroscopic analysis, light is defined by the wavelength (and not by the applied energy). If this sounds new, you can refer to the first blog article of this series:

What is NIR spectroscopy?

The wavelength of light is inversely correlated to its energy. Therefore, the smaller the wavelength, the more energy there is. The electromagnetic spectrum is shown in Figure 1. The NIR region lies between the visible region (higher energy) and the infrared region (lower energy) at 780 to 2500 nm.

Light from both the IR and NIR region of the electromagnetic spectrum induces vibrations in certain parts of molecules (known as functional groups). Thus, IR and NIR spectroscopy belong to the group of vibrational spectroscopy. Figure 2 shows several functional groups and molecules that are active in the NIR region.

Advantages of NIR spectroscopy over IR spectroscopy

The theoretical outline above lets us derive the following advantages of NIR over IR spectroscopy.
 

Lower intensity of bands with NIRS, therefore less detector saturation

For solids, you can use pure samples as-is in a vial suitable for NIR analysis. With IR analysis, you either need to create a KBr pellet or carefully administer the solid sample to the Attenuated Total Reflectance (ATR) window, not to mention cleaning everything thoroughly afterwards.

For liquids, NIR spectra should be measured in disposable 4 mm (or 8 mm) diameter vials which are easy to fill, even in the case of viscous substances. IR analysis requires very short pathlengths (<0.5 mm). Either costly quartz cuvettes or flow cells are needed, neither of which are easy to fill.
 

Higher energy light with NIRS, therefore deeper sample penetration

This means NIRS provides information about the bulk sample and not just surface characteristics, as with infrared spectroscopy.
 

NIRS can be used for quantification and for identification

Scientists often use infrared spectroscopy to detect the presence of certain functional groups in a molecule (identification only). In fact, quantification is one of the strong points of utilizing NIR spectroscopy (see below).
 

NIRS is versatile

NIR spectroscopy can be used for the quantification of chemical substances (e.g., moisture, API content), determination of chemical parameters (e.g., hydroxyl value, total acid number) or physical parameters (e.g., density, viscosity, relative viscosity, and intrinsic viscosity). You can click on these links to download our free Application Notes for each example.
 

NIRS works with fiber optics

This means you can easily transfer a method from the laboratory directly into a process environment using an analyzer with a long, low-dispersion fiber optic cable and a rugged probe. Fiber optic cables are not possible to use with infrared radiation due to physical limitations.

NIR ≠ IR spectroscopy

In summary, NIR is a different analytical method than IR, although both are types of vibrational spectroscopy. NIR is faster and easier to handle than IR. It does not require sample preparation and can provide information about the bulk material. It is also versatile. NIR spectroscopy allows for the quantification of different kinds of chemical and physical parameters and can also be implemented in a process environment.

Watch our video to learn about the major differences between IR and NIR spectroscopy.

In the next installment of this series, we focus on the process of implementing a near infrared spectrometer in your laboratory workflow, using a specific example.

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