Inline moisture analysis in fluid bed dryers by near-infrared spectroscopy

Importance of Topic

The control of residual moisture in fluid bed drying is critical in pharmaceutical manufacturing. Inadequate drying can cause particle fractures or caking, affecting downstream processing and final product quality. Real-time monitoring enables timely process decisions, reducing waste and ensuring consistent product performance.

Objectives and Study Overview

This application note demonstrates the implementation of inline near-infrared spectroscopy (NIRS) for moisture monitoring in a fluid bed granulator/dryer. The goal is to replace slow offline weight-loss methods with continuous, non-destructive analysis, improving process efficiency and product quality.

Methodology and Instrumentation

Development of a calibration model correlates NIRS spectra to laboratory reference moisture values. A specialized NIRS “spoon” probe is inserted into the dryer, collecting spectra every 30 seconds. An air purge clears the probe tip between measurements, ensuring representative sampling. Data are transmitted to a Process Analyzer and can be integrated with a PLC or process control system.

Used Instrumentation

• NIRS XDS Process Analyzer – MicroBundle SinglePoint (1100–1650 nm range)
• Micro-interactance reflectance probe with purge-on-collection tip
• Fiber-optic connection up to 35 m from analyzer to probe

Main Results and Discussion

Inline NIRS provided continuous moisture trends that closely matched offline reference assays. The real-time moisture profiles enabled precise determination of the drying endpoint, avoiding over-drying or under-drying. Integration with control systems facilitated automated cut-off decisions, minimizing operator intervention and product rework.

Benefits and Practical Applications

Implementing inline NIRS moisture analysis offers:

• Fast, reagent-free, non-destructive measurements
• Elimination of manual sampling delays
• Improved process understanding and control
• Reduced reprocessing, saving time and costs
• Enhanced product quality through consistent moisture control

Future Trends and Potential Applications

Advancements may include machine-learning models for more robust calibration, multi-component monitoring in combined granulation and coating processes, and tighter integration with advanced PAT frameworks. Extending inline NIRS to other steps—such as blend homogeneity, solvent purity, or lyophilized products—can further optimize pharmaceutical manufacturing.

Conclusion

Inline NIRS moisture analysis in fluid bed dryers streamlines process control, reduces product risks, and supports regulatory PAT initiatives. The technology’s speed and precision deliver tangible economic and quality benefits, positioning NIRS as a key tool for modern pharmaceutical production.

Reference

• AN-PAN-1050 Inline moisture analysis in fluid bed dryers by near-infrared spectroscopy, Metrohm Process Analytics
• AN-PAN-1048 Inline moisture analysis in a pilot scale granulation process by NIRS
• AB-358 Analysis of residual moisture in a lyophilized pharmaceutical product by NIRS