Applications of the Tunable Diode Laser Absorption Spectroscopy: In-Process Estimation of Primary Drying...

Area of Science:

• Pharmaceutical Sciences
• Chemical Engineering
• Process Analytical Technology

Background:

• Accurate prediction of product temperature during primary drying is critical for successful lyophilization.
• Existing models rely on ice sublimation rate (dm/dt) and vial heat transfer coefficient (Kv), which can exhibit significant variability.
• Variations in Kv between vial suppliers can lead to erroneous temperature predictions.

Purpose of the Study:

• To evaluate the impact of dm/dt measurement variability and Kv on product temperature prediction during lyophilization.
• To introduce and validate a new approach for calculating drying heterogeneity.
• To assess the performance of a tunable diode laser absorption spectroscopy (TDLAS) sensor for dm/dt measurement.

Main Methods:

• Utilized a second-generation TDLAS sensor for real-time dm/dt measurement.
• Calculated Kv and assessed intersupplier variability for identical vial types.
• Developed and applied a novel method to estimate batch drying heterogeneity during primary drying.

Main Results:

• TDLAS dm/dt measurements showed good agreement (5%-10% difference) with gravimetric methods across scales.
• Significant intersupplier variability in Kv was observed, highlighting risks of using generic values.
• TDLAS-derived product temperatures were within ±1°C of thermocouple measurements during primary drying.
• The new approach for estimating drying heterogeneity demonstrated good agreement between theoretical and experimental outcomes.

Conclusions:

• TDLAS is a reliable method for measuring dm/dt in lyophilization, improving temperature prediction accuracy.
• Acknowledging and accounting for Kv variability is essential for precise product temperature modeling.
• The developed method for assessing drying heterogeneity provides valuable insights into batch uniformity.