Sampling solutions for NIRS Process Analyzers

Significance of the Topic

Near-infrared spectroscopy (NIRS) offers real-time, noninvasive, reagent-free monitoring of solids, liquids, suspensions and gases in industrial settings. Its rapid, high-resolution spectral output supports both qualitative and quantitative analyses without elaborate sample preparation, making it a key technology for process control and quality assurance.

Objectives and Study Overview

This work provides a comprehensive guide to selecting and implementing sampling solutions for process NIRS analyzers. It outlines the advantages, limitations and best practices for probes, flow cells and fiber-optic interfacing across different sample types and conditions.

Methodology and Instrumentation

The study classifies sample streams by phase and complexity and matches them to suitable measurement modes—transmission, transflection, diffuse reflectance or non-contact. Key instrumentation includes:

• NIRS Analyzer Pro and NIRS XDS Process Analyzer
• Single-fiber and microbundle optical fibers (silica core, low-dispersion, up to 200 m length)
• Inline and online sampling modules: flow cells, immersion probes, clamp-on cells, spoon probes and non-contact probes
• Materials: stainless steel (316L), Hastelloy, PTFE and specialty polymers for corrosive or high-temperature streams

Sampling modules are connected via standards (Swagelok®, flanges) and integrated with industrial PCs and PLC/DCS protocols for continuous feedback.

Key Results and Discussion

Optimal sampling ensures reproducibility and precision:

• Transparent liquids achieve best results in transmission cells with controlled optical path lengths (0.5–5 mm) and temperature control.
• Corrosive or high-temperature streams require PTFE flow cells, transmission probe pairs or cooled fiber probes rated to 250–300 °C and 5 000 psi.
• Powders and opaque solids are measured by diffuse reflectance probes (contact or non-contact) with adjustable standoffs to average heterogeneous surfaces.
• Macroscopic particles and films use non-contact probes at defined distances (10–300 mm) to balance spot size and signal-to-noise.
• Suspensions (> 30 wt% solids) rely on reflectance; lighter slurries use transmission probes after centrifugation or filtration if needed.
• Gaseous streams reach quantification via long-path transmission cells (centimeters to meters), with precise pressure and temperature control following the ideal gas law.

Implementation guidelines emphasize laminar flow in flow cells, regular cleaning protocols (steam or solvent), and probe immersion depth aligned with representative sample zones.

Advantages and Practical Applications

The integrated sampling solutions enable:

• Continuous 24/7 monitoring without chemical reagents or waste.
• Multiplexing of up to 16 sampling points per analyzer for comprehensive process mapping.
• Safe operation in hazardous zones through remote fiber-optic placement.
• Flexible customization to handle a wide scan range (800–2200 nm) across diverse industries—pharma, polymers, food, petrochemicals.

Future Trends and Opportunities

Advances in fiber-optic materials, miniaturized probe designs and higher-resolution detectors will expand NIRS applications to more extreme conditions. Integration with Industry 4.0 platforms, machine learning for spectral interpretation and real-time feedback control loops will further boost process efficiency and product quality.

Conclusion

Effective process NIRS hinges on matching sample properties to the right measurement mode and sampling hardware. Metrohm Process Analytics’ portfolio—from robust PTFE flow cells to customizable fiber-optic probes—ensures reliable, high-throughput analysis across industrial applications.

Used Instrumentation

• NIRS Analyzer Pro
• NIRS XDS Process Analyzer
• Single-fiber and microbundle fiber-optic cables
• Inline/online probes and flow cells (stainless steel, PTFE)
• Industrial PC, PLC/DCS interfaces