Analysis of chemicals using near-infrared spectroscopy

Importance of the topic

NIR spectroscopy has become a cornerstone technique in industrial and research laboratories for rapid, non-destructive chemical analysis. Its sensitivity to O–H, N–H and C–H bonds enables direct measurement of moisture, reactants and products in liquids, slurries and solids without chemical reagents. This flexibility supports real-time process control, improves safety and reduces waste.

Goals and overview of the bulletin

This Application Bulletin compiles 68 case studies illustrating both qualitative differentiation and quantitative determination of chemical species in the chemical industry. Key objectives are:

• Demonstrate NIR feasibility for a wide range of analytes from trace water in organic solvents to polymer and resin monitoring.
• Present recommended sampling methods, instrument configurations and chemometric approaches.
• Highlight examples of at-line, in-line and on-line applications in process streams and bulk materials.

Methodology and instrumentation

Measurements were performed in transmission, reflectance and interactance modes over the 400–2500 nm range using NIRSystems Model 5000 and 6500 spectrometers, Metrohm NIRSystems XDS RapidLiquid, XDS SmartProbe and XDS RapidContent analyzers, and Process Analytics Model 5500. Fiber-optic probes, spinning sample cups and cuvette modules provided flexible sampling for liquids, powders and coated films.

• Transmission cuvettes (1–20 mm pathlength) for low-absorbance liquids
• Reflectance/remote probes and coarse sample cells for powders, films and solids
• Interactance immersion probes for turbid and high-scatter samples
• Temperature-controlled modules for high-temperature streams

Main results and discussion

The bulletin demonstrates successful NIR calibrations and qualitative models for:

• Moisture determination down to tens of parts-per-million in solvents such as monochlorobenzene, methyl isocyanate and phenol.
• Quantitation of organics including methyl acetate, methanol, surfactants, amines, fatty acids, polymers and fragrances across 0.05–100 % ranges.
• Reaction monitoring and endpoint detection for hydrofluoric/sulfuric acid mixtures, alkylation, polymerization and amine derivatization.
• Coating thickness and solid composition analysis in films, propellants, tied resins and catalytic materials.

Benefits and practical applications

NIR spectroscopy offers numerous advantages for industrial analytics:

• Rapid results (seconds per sample) enable real-time decision making.
• No chemical reagents or sample preparation reduce cost, waste and exposure hazards.
• Versatile sampling options (lab, at-line, in-line and on-line) integrate seamlessly into process control systems.
• Multivariate calibrations allow simultaneous monitoring of multiple analytes in complex matrices.

Future trends and possibilities

Advances in miniaturized spectrometers, higher-speed detectors and cloud-based chemometric platforms will further extend NIR applicability. Future developments include:

• Real-time process analytical technology (PAT) integration with advanced feedback control.
• Automated model updating and robustness monitoring using machine learning.
• Portable and handheld NIR sensors for field applications and mobile quality assurance.
• Combined NIR-Raman and NIR-infrared imaging for enhanced spatial–chemical mapping.

Conclusion

This comprehensive set of case studies confirms that near-infrared spectroscopy is a versatile, accurate and efficient tool for chemical analysis across research, quality control and process monitoring. Adoption of NIR methods can streamline workflows, reduce laboratory burden and deliver real-time insights to optimize production and ensure product quality.

References

No external literature references were supplied in the source document.