Using NIR for Greater Process Control

Process optimization is extensively recognized as an essential requirement of chemical production facilities, yet it usually remains an at line or offline task. Real applications undergo uncertainty and process disturbances and thus, there is obviously a requirement for deeper process understanding through on-line real time analytical measurements.

For in-situ applications, the observation window is the eye to the process when using optical analysis methods. A clean observation window will allow reliable analysis at any time during biological and chemical processes. Thus, the use of optical techniques is only possible when the following procedures are implemented reliably and at any time:

  • Cleaning of observation window
  • Cleanliness check of the observation window
  • Active control over the whole analyzer
  • Zero baseline at any time
  • Complete cleaning of all parts which have contact with product (seals, surfaces, etc.) following the guidelines of GMP, Hygiene etc.

Application Examples

Refinery Production

NIR measurements are controlled by CH components of the samples and as such, they are beneficial for the determination of high concentrations. In certain cases, there is an advantage in measuring extra functional groups by means of MIR immersion probes that can monitor specific compounds. (Aliphatic vs. aromatic)


NIR transmission can establish bulk components composition and allow calculations of octane numbers. MIR in specific wavenumber ranges can be useful for the determination of additives and/or impurities.


In the production of bio-fuels, process control can be done before and after purification. Normally, the NIR region contains combination and overtone information with the most sensitive bands being derived from C-H and O-H bonds. Again, MIR process control data from fiber optic immersion probes can be used to determine additives and/or impurities.


MIR measurement has benefits for compositional monitoring, particularly when measuring process mixtures and in searching for and confirming impurities.

Specialty Chemicals

For agrochemicals, water treatment, dyes and pigments, reflectance measurements and ATR measurements can be used. MIR would mainly be used for traces analysis and NIR for bulk analysis.

Food Products

This is an area where NIR has been used very well, so any benefits that MIR could offer would be for specific lower level compound analysis. There could be some scope for an integration of NIR and MIR in analysis of fragrances, flavors and fermentations. In addition, there may be benefits of combining data, mainly in fermentation. A few of the categories might have some scope for a transmission probe but the majority needs a reflectance monitoring probe (e.g. oils dairy, and fats).

Pharmaceutical Products and their Development

Split into two depending if material is a liquid or a solid. A combination of wavelength regions in a reflectance probe can be used for composition monitoring where MIR fiber optics can establish low concentration compounds and NIR fiber optics for main components.

Measurement Examples

Dairy production: wash cycle.

Sunflower oil production monitoring.

Olive oil production monitoring.

Attenuated Total Reflection (ATR) Immersion Probe

A variety of fiber optic ATR Immersion Probe for process spectroscopy applications is available. Sealed diamond or ZnSe tips offer high contrast evanescent absorption spectra in the temperature range of 0-140 °C.

Attenuated Total Reflection (ATR) Disposable Loop

PIR fiber probes in the 3-18 µm range with detachable PIR fiber loops have been engineered to provide a cost effective substitute to diamond ATR-IR fiber probes.

Lighthouse Probe

The Lighthouse Probe® can be used with a range of spectroscopic methods, including UV/VIS and NIR, to overcome the traditional issue of product sticking to observation windows. It is compact and easy to install, and allows taking a reliable in-process measurement of quality critical product features.

Ceramat® WA 150

The Ceramat® WA 150 has an automatic sensor lock-gate for challenging applications with ceramic sealing to the process. Even when the process medium is corrosive, toxic, hot, and under pressure, it stays reliably sealed off.

SensoGate® WA 130

The SensoGate® WA 130 has universal, pneumatically operated retractable fitting with modular design. The central multi-plug contains tubings for cleaning, rinsing and calibration media, including limit switches and check valves and allows a rapid, safe and space-saving connection.

This information has been sourced, reviewed and adapted from materials provided by art photonics GmbH.

For more information on this source, please visit art photonics GmbH.

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