FT-NIR Frequently Asked Questions

Fourier transform near-infrared (FT-NIR) spectroscopy has become the method of choice for many companies producing and analyzing polymers and plastics. FT-NIR has many advantages in comparison with traditional analytical methods. Noninvasive and nondestructive analyses can be performed, reagents are not typically required, prep time is minimal, and samples can be analyzed in situ through glass or polymer containers.

We have written about the use of FT-NIR spectroscopy for the determination of the hydroxyl value and other critical polyol properties to help improve polyol product quality, verification of the plasticizer content in PVC, and analysis of the density and copolymer content in polyethylene samples. Since FT-NIR analysis can be vital to optimizing your manufacturing processes, increasing your plant’s yield and solving some of your industrial quality control problems, you may want to get more details about this technology.  Here are the answers to some of our most frequently asked questions about FT-NIR.

What is FT-NIR?

Fourier transform near-infrared spectroscopy (FT-NIR) is a non-destructive chemical analysis technology that provides a means to identify and analyze various materials.

What are the advantages of FT-NIR versus a dispersive NIR?

FT-NIR systems have advantages in higher resolution, better wavelength accuracy, higher signal energy and are more stable and repeatable. FT systems do not require software standardization for method transfer between instruments. Also FT systems are not affected by stray light which causes sampling challenges for dispersive systems.

What is PLS?

Partial Least Squares (PLS) is a statistical approach to quantitative analysis. PLS models correlate spectral variation with component concentration variation to create models for components predictions.

What is reflection analysis by NIR?

Samples in cups, bags, vials or set directly on the integrating sphere are interrogated by NIR light energy and the light is transmitted, directly reflected, absorbed and diffusely reflected. The diffusely reflected light is collected and sent to a detector. By collecting the amount of light that is diffusely reflected from solid samples you can predict component concentrations or identify samples.

What is transmission analysis by NIR?

Samples in tubes, cuvettes or vials are held in a module and interrogated by NIR light energy. The source light can be transmitted, directly reflected, scattered, absorbed and diffusely reflected from the samples. The light that transmits through the sample is collected by a detector. By collecting the amount of light that is transmitted thru a sample you can predict component concentrations or identify samples.

How many samples are required to develop and validate a calibration?

It depends on how challenging the application is, how many components will be in the calibration and if the most ideal standards are used for calibration development.

Transmission analysis on liquids often requires fewer standards than reflection analysis especially on in-homogeneous solids. More components require more standards in the calibration model than a single component model. Standards used in NIR calibration models must take into account all the chemical, physical and sampling variation that the calibration will be exposed to when implemented for QC testing.  For some applications an ideal standard set can by synthetically generated in the lab but when pulling samples off production process running within specification it takes a lot of standards to model in all the needed variation. At a minimum 10 times the number of components in the calibration model will generate a starter calibration to prove feasibility of the calibration.

Want more information about NIR?  Click here to access our many recorded FT-NIR webinars for chemicals and polymers.

Do you have additional questions?  Comment below and let us know and we may add it to our list.