Demand for reliable methods of preparing and storing highvalue samples has rejuvenated the market for freeze-dryers, also known as lyophilizers. In response, vendors have transformed freezedryers from clunky, homemade agglomerations of pumps, flasks, and cold traps to precision instruments under strict computer control. Freeze-drying removes close to 100 percent of the water from a sample, leaving behind either the structural framework of plant or animal tissues or powdery chemicals, proteins, or residues.
One of the most significant trends in freeze-drying instrumentation has been the integration of lyophilization’s three steps (freezing, primary drying, and secondary drying) into a single, miniaturized instrument.
Freeze-drying is hard on vacuum pumps, which is why Labconco includes a moisture detector in the drain lines of some units. The sensor prevents the pump from turning on in the presence of significant moisture. “The last thing you want is to ruin your pump by having it suck in a liter of melted ice,” says Labconco product manager Jenny Sprung. Pumps can also slowly be ruined by units with coils that cannot handle the volume of sublimate.
Freeze-drying requires close control over freezing rate, drying temperature, and pressure in order to prevent product melt-back, which occurs when the product temperature rises above its critical point.
Product temperature is controlled by adjusting the shelf temperature. It may still vary significantly, however, depending on its thickness, the solids content, the thickness of the dry layer during primary drying, and the equipment’s condensing rate and heat transfer dynamics.
Historically, drying temperature is adjusted by trial and error until a suitable freeze-drying process is established for a particular quantity of a specific product. Subsequent runs are conducted according to that protocol, without in-process temperature monitoring.
This empirical approach requires numerous trial runs, which may be unreasonable to perform at scale with very high-value products. “So the goal should be to achieve an acceptable freeze-drying protocol in a single test run,” says T.N. Thompson, president of Millrock Technology (Kingston, NY). Millrock has championed a technique, Auto-Dry, to assist in achieving rapid optimization.
Auto-Dry generates a baseline protocol based upon user input. It consists of a software algorithm and a PLC (programmable logic controller) that can replace the existing controller.
Once the baseline protocol is established, the freeze-dryer automatically adjusts the shelf temperature to minimize freeze-drying time while keeping the product well below its critical temperature.
Auto-Dry automatically detects the end of primary drying and advances to secondary drying using either a conservative or an aggressive profile.
With conventional freeze-drying, the operator needs to monitor product temperature and manually adjust shelf temperature over the entire course of the lyophilization. The result is typically a long, conservative cycle. “Reducing lyophilization time is critical for keeping operating costs to a minimum,” Mr. Thompson notes.
Lastly, when considering the purchase of a freeze-dryer all but the most experienced users should consult with an expert to determine which configuration and features best fit the user’s needs.
- Features trap cooling temperature of up to -45ºC
- Ice holding capacity is 1L/time
- Safety features include: automatic operation for vacuum pump, monitoring for vacuum degree and trap temperature, stop watch, selecting the setting for power recovery
- Includes sheet key type, digital display
- Include ice holding capacity for light to moderate loads and have dual refrigeration systems for samples with very low eutectic points
- Provide a compact benchtop design and include a 12-port drying chamber
- -105°C 4.5 liter systems remove over 4 liters of water in 24 hours
Benchtop™ K Series Manifold
- Ease of use is ensured by one button start-up that activates all operating parameters in the correct sequence
- Employ environmentally friendly CFC-free refrigeration systems
- Condenser temperatures from range -55ºC to -105ºC
- Equipped with the Sentry 2.0 user-friendly control system
Freeze Dryer w/ concentrator
- Works well for samples with solvent
- Prevents bubbling of a sample within the tube by a strong centrifugal force; permits 100% recovery
- “Concentrator” can concentrate & dry using various capa city tubes from 1.5 ml micro- tubes to 50 ml tube