How do NIR work?
Near-infrared spectroscopy probes overtones and combination bands of fundamental molecular vibrations, mainly of hydrogen-bearing groups such as O-H, N-H and C-H. Absorption in this region is weak, so light penetrates millimeters to centimeters into powders, grains and liquids, which allows bulk measurement with little sample preparation. Instruments use a polychromatic source and either a Fourier transform interferometer or a grating with a detector array to record reflectance, transmission or transflectance spectra. Because the bands are broad and overlapping, composition is predicted with multivariate calibration models built from a set of reference samples analyzed by a primary method such as Karl Fischer titration, Kjeldahl nitrogen or HPLC. Models use algorithms such as partial least squares regression and are validated for the specific product, instrument and measurement conditions.
Which NIR variants are available?
- Benchtop FT-NIR Analyzer — A benchtop FT-NIR analyzer uses an interferometer to record high-resolution near-infrared spectra of powders, liquids and solids.
- Dispersive Grating NIR Spectrophotometer — A dispersive grating NIR spectrophotometer uses a fixed grating and a detector array to capture near-infrared spectra quickly and without moving parts.
- Handheld NIR Analyzer — A handheld NIR analyzer is a battery-powered device for point-and-shoot identification and composition checks outside the laboratory.
- Online NIR Process Analyzer — An online NIR process analyzer measures composition continuously through fiber-optic probes installed on reactors, dryers, blenders or pipelines.
- NIR Chemical Imaging System — An NIR chemical imaging system captures a complete spectrum at every pixel of a sample surface.
How do I choose the right variant?
Choose a NIR system from the sample form and the regulatory context, because the calibration model is often more valuable than the hardware. Benchtop FT-NIR analyzers suit laboratories that need high resolution and stable performance for many product models. Dispersive grating instruments with array detectors are compact and fast for routine quality checks. Handheld analyzers serve incoming material identification and field work. Process analyzers with fiber-optic probes measure at the reactor, dryer or blender. Chemical imaging systems map heterogeneity. For every option, confirm that validated calibrations exist or can be developed, and check wavelength range, resolution, photometric stability and whether the instrument can transfer models from another site.
Where are NIR used?
NIR are specified in raw material identification at goods receipt, moisture, protein, fat and starch determination in food and feed, pharmaceutical blend uniformity and tablet content monitoring, online polymer, chemical and petrochemical process control, agricultural grain and seed quality grading and textile, paper and material composition screening.
Which standards and certifications apply?
Work with NIR is commonly governed by Ph. Eur. 2.2.40 Near-infrared spectrophotometry, USP <1119> Near-Infrared Spectroscopy, ASTM E1655 Standard Practices for Infrared Multivariate Quantitative Analysis, ISO 12099 Guidelines for the application of near infrared spectrometry, ICH Q2(R2) Validation of analytical procedures, ISO/IEC 17025 and IEC 61010-1. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Near-infrared results depend on representative sampling because the measurement volume is small relative to a batch. Sample presentation, particle size, packing density, temperature and moisture all shift spectra, so operators must follow a fixed procedure. Calibration models require ongoing maintenance: performance checks against reference samples, outlier detection, and updating when raw materials, processes or instruments change. Reference analyses must be accurate because model errors persist. Instruments should be qualified and models validated before use, with change control for software and calibration updates. Install units on stable benches or in the plant with protection from vibration, dust and temperature swings.
