Monitoring pharmaceutical solvent drying processes using the Prima PRO Process Mass Spectrometer

Monitoring Pharmaceutical Solvent Drying Processes with the Prima PRO Process Mass Spectrometer

Importance of the topic

The drying step is critical in pharmaceutical manufacturing because residual solvents and water influence product quality, polymorphic form, stability and downstream processing. Traditional end-point laboratory assays (loss on drying, gas chromatography, Karl Fischer titration) are time-consuming and often push manufacturers to over-dry material to avoid batch rework. Real-time process monitoring that reliably quantifies multiple volatile components during vacuum and atmospheric drying enables better process control, reduced cycle times, higher throughput and improved product quality—key objectives of the FDA's Process Analytical Technology (PAT) initiative.

Objectives and overview of the application note

• Review how on-line process mass spectrometry can be applied to solvent drying in pharmaceutical dryers (vacuum, tray, rotary).
• Describe limitations of alternative in situ spectroscopic probes and early mass spectrometry implementations.
• Present the design features and analytical performance of the Prima PRO Process Mass Spectrometer (magnetic sector analyzer with a variable pressure inlet) and how these enable reliable quantitative monitoring and process control.

Methodology and approach

• Sampling strategy: headspace sampling or downstream sampling from the dryer outlet (vacuum suction line or outlet air) using a Swagelok-type connection, a heated sample line and a particulate filter with disposable element to protect the analyzer and maintain representative sampling of bulk material.
• Analyzer operation: continuous on-line gas analysis with the analyzer maintained at a constant internal pressure to avoid signal variation when process pressure changes from atmospheric to vacuum.
• Quantification: use of distinctive fragmentation patterns (mass spectral fingerprints) and introduction of calibration gases under software control to convert ion currents into solvent concentrations rather than qualitative signals.

Instrumentation used

• Prima PRO Process Mass Spectrometer (Thermo Scientific) featuring a magnetic sector analyzer with a laminated magnet for high stability and rapid scanning comparable to quadrupoles.
• Variable pressure inlet (multipoint available) with two opposing control valves to maintain analyzer pressure at ~0.1 mbar while handling sample pressures down to ~0.3 mbar; enables sampling from multiple dryers (up to 10) or single-point inlet for R&D/pilot use.
• Heated transfer lines, basic particulate filtration, sample manifolds and vacuum pumping trains as part of the sampling system.
• GasWorks Quantitative Software for data reduction, calibration, and delivery of concentration results; 21 CFR Part 11 compliance and standard process communication protocols for integration with process control systems.

Main results and discussion

• Analyzer performance: magnetic sector design offers markedly improved precision and stability versus quadrupole analyzers—reported precision typically 2–10× better depending on analytes and mixture complexity. Key features include an enclosed ion source (high sensitivity, low background) and a high-energy (1000 eV) source to ensure rugged operation in the presence of potentially contaminating vapors.
• Variable pressure inlet function: the dual-valve inlet controls analyzer pressure precisely (0.1 mbar setpoint), avoiding the signal artifacts that occur when process pressure swings are uncontrolled. This allows robust switching between streams at widely different pressures and supports multipoint monitoring without long stream-switching delays.
• Quantitative drying traces: example two-solvent drying curves demonstrate simultaneous, time-resolved monitoring of water and isopropanol removal as dryer pressure falls from atmospheric to ~2 mbar while inlet pressure remains constant—enabling real-time determination of residual solvent concentrations.
• Contamination resistance and maintenance: the magnetic sector instrument exhibits reduced sensitivity to hydrocarbon contamination relative to quadrupoles, leading to longer intervals between calibrations and maintenance. The unit is supplied with a plug-and-play service kit and benefits from a three-year parts-and-labor warranty.

Benefits and practical application of the method

• Real-time quantitative data support PAT objectives: direct, continuous insight into drying kinetics and end-points reduces reliance on delayed laboratory assays and minimizes over-drying.
• Greater process throughput and reduced downtime: accurate end-point detection avoids unnecessarily long drying cycles and the associated capacity and scheduling penalties.
• Multiplexed monitoring: a multipoint inlet can sample multiple dryers, enabling plant-wide or multi-line process understanding with a single analyzer.
• Simplified sampling vs. in situ probes: headspace or outlet sampling avoids problems of probe fouling, non-representative spot sampling, retractable probe mechanics in paddle dryers, and complex chemometric models sometimes required by bulk spectroscopic methods when multiple solvents are present.
• Seamless control integration: quantitative outputs and industry-standard communications enable closed-loop or supervisory control strategies to actively optimize drying recipes in real time.

Future trends and potential applications

• Tighter integration with advanced process control: mass spectrometry outputs can be fed to predictive models and model-predictive control loops to further reduce cycle times and variability.
• Expanded multicomponent quantification: combining robust magnetic sector stability with enhanced spectral deconvolution and larger calibration libraries will simplify monitoring of complex solvent mixtures and trace-level impurities.
• Digitalization and compliance: deeper software integrations, cloud-enabled analytics and audit-ready data management will strengthen regulatory compliance and remote process monitoring.
• Broader industrial adoption: the same approach can be extended beyond pharmaceutical drying to solvent recovery systems, vacuum distillation, continuous manufacturing lines, and environmental VOC monitoring within production facilities.

Conclusion

On-line process mass spectrometry, when implemented with a stable magnetic sector analyzer and a well-controlled variable pressure inlet, provides a reliable, quantitative and contamination-resistant solution for monitoring solvent drying in pharmaceutical processes. The Prima PRO system addresses the historical limitations of spectroscopic probes and early quadrupole-based mass spectrometers by delivering improved precision, robust multipoint sampling, and software-driven quantitative outputs suitable for PAT-driven process control. The result is better process understanding, reduced over-drying and improved manufacturing efficiency and product quality.

Reference

• Application note: Monitoring pharmaceutical solvent drying processes using the Prima PRO Process Mass Spectrometer. Thermo Fisher Scientific, Winsford, Cheshire, United Kingdom. Author: Graham Lewis. EPM-AN1452-EN 6/25, © 2025 Thermo Fisher Scientific Inc.