Sampling solutions for NIRS Process Analyzers

Significance of the topic

Near-infrared (NIR) spectroscopy delivers rapid, reagent-free, noninvasive analysis of solids, liquids and gases, making it indispensable for industrial quality control, process monitoring and regulatory compliance. By combining high resolution, broad spectral range and real-time feedback, NIR enables efficient optimization of production, improved safety and reduced operating costs.

Study objectives and overview

This application whitepaper from Metrohm Process Analytics presents a comprehensive guide to selecting optimal sampling solutions for NIR process analyzers. It reviews measurement principles, probe and flow-cell designs, fiber-optic interfaces and system architectures, aiming to help end users achieve reproducible, accurate in-process data for academic research or industrial quality assurance.

Methodology and instrumentation used

The document outlines key NIR measurement modes—transmission, transflectance, reflectance and non-contact—and matches them with sampling interfaces suited to various sample states and process conditions. It details:

• Probes and flow cells in stainless steel, Hastelloy, titanium or PTFE for chemical and temperature resistance
• Flow-through cells for bypass lines, clamp-on cells for noninvasive installation and transmission/transflectance probe pairs for extreme pressures and temperatures
• Immersion and non-contact probes for powders, pellets, films and large particulates
• Fiber-optic assemblies: single fibers (600 µm core) for clear liquids and microbundle fibers (37 or 2×37 strands) for enhanced signal-to-noise
• Ancillary components: 2060 Human Interface, industrial PC, PLC/DCS communication

Main results and discussion

The brochure categorizes sampling strategies by sample type:

• Clear liquids: transmission flow cells or single-pass probes with OPL tuned for water content
• Corrosive streams: PTFE or PFA cells and PTFE-sleeved transflection probes
• Solids and powders: reflectance probes and diffuse reflectance/transmission modules for opaque samples
• Suspensions and slurries: reflectance for high solids, transmission for low solids with pretreatment where needed
• Gases: long-path transmission cells with pressure and temperature control for continuous or batch measurement
• Non-contact: remote focal-plane probes for moving films, pellets or heterogeneous materials

Key considerations include path length, immersion depth, flow regime, fiber protection and ease of maintenance.

Benefits and practical applications

Customized NIR sampling solutions deliver:

• 24/7 real-time monitoring without reagents or chemical waste
• Multiplexing up to 16 measurement points per analyzer
• Rapid process feedback to maximize yield and product consistency
• Wide 800–2200 nm spectral coverage for diverse chemistries
• Adaptation to harsh or classified environments via remote fiber routing

Applications span polymer extrusion, chemical reactors, pharmaceutical drying, food processing and environmental gas analysis.

Future trends and potential uses

Emerging developments will center on integration with advanced chemometric and machine-learning platforms, digital-twin process models, automated calibration routines and modular sensor networks. Extended fiber lengths, improved low-temperature probes and smart sampling panels will further expand in-line analytics in bioprocessing, petrochemicals and flexible manufacturing.

Conclusion

Effective process analytics requires not only a high-performance NIR spectrometer but also a tailored sampling interface. Metrohm Process Analytics leverages over 45 years of expertise to deliver customized probe, flow-cell and fiber solutions that ensure robust, reproducible, high-quality data under any industrial condition.

References

• Metrohm Process Analytics. Sampling solutions for NIRS. Brochure, 2021.