Tunable Diode Laser Absorption Spectroscopy (TDLAS)

TDLAS is a non-invasive spectroscopic method for the determination of the concentration of a gas or a gas component. A laser beam is generated by a NIR-Laser and launched through the sample, the absorption spectrum is recorded and allows accurate measurement of gas concentrations with detection limits < 10^-5 ppm. In freeze-drying, the concentration of water vapor in the gas phase is continuously determined in the spool piece between chamber and condenser. Since the TDLAS unit is installed at an angle relative to the duct, the beam is subjected to a Doppler shift resulting in a wavelength shift of the absorption spectrum. The comparison of this spectrum to a reference allows calculation of flow velocity and of mass flow rates through the spool piece. Mass flux measurements can be integrated to provide an estimate of mass removed and a thereby information about the status of the process. Since there is no contact between the TDLAS unit and the sterile area, the use in both R&D and manufacturing freeze-dryers is possible for process control under aseptic conditions. A combination with MTM technology appears desirable for the design and optimization of lyophilization cycles and calculation of process parameters in pre-existing cycles. TDLAS is also a useful tool for operational qualification of freeze-dryers as well as scale-up and transfer of lyophilization processes from one freeze-dryer to another.

Figure: Technical setup of TDLAS apparatus

Back to Home

Back to Research