Automated freeze-drying

In a freeze drying plant automated in this way, the desorption rates and the desorbable water content (in % of solids) can be measured, calculated and documented. 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

The control system of the freeze-drying unit provides control, monitoring and documentation of the process. Such a system must be reliable and comply with GM P and GAMP (Good Automation Manufacturing Practice) demands with respect to computer validation. It should be SCADA (Supervisory Control and Data Acquisition) compatible. A possible hardware architecture is shown in Figure 2.55.1. 

This section describes the automation of freeze-drying processes. The automatic loading and unloading a freeze-drying plant can be found in Section 2.4.1. 

Collection of the purified material is accomplished by diverting flow into an appropriate sized vessel as the peak of interest passes through the detector. Valves are available to facilitate or even automate this operation. Recovery can be accomplished by evaporation (normal phase), by freeze drying (reverse phase), or by extraction from an aqueous phase (reverse phase) into an organic solvent followed by evaporation. Obviously solvent impurities are of concern when recovering the compound of interest since these impurities... 

At first sight, then, complex mechanical setups as we propose for semicon-tinuous or continuous freeze-drying seem susceptible to serious hazards in the sterility control of the operation. However, this is not as dramatic as it looks since the essential part of the process—if not the entire process—is carried out automatically and can be done entirely within a sterile environment by remote control. Indeed, today highly sophisticated automation can be achieved if we resort to the advanced technologies developed for the nuclear industry and profit by the experience of their operators. However, this sophistication will definitely bear on the cost and this can be a serious drawback for conventional low-priced products. 

Changes and advances in mechanical design of freeze-drying equipment and control systems have had a strong impact. Modem freeze-dryers are easier to use, require less operator intervention and are applicable to a wide variety of products. Current, automated freeze-dryers allow the initial steps of the protocol to be implemented, thereby providing the operator with more data of interest also, they are safer and easier to operate than previous models. 

Freeze-drying has rarely been considered an effective choice with a view to automating sample pretreatment, possibly because of the contradictory results obtained so far. However, there is solid evidence that this technique is suitable for many purposes. 

The first chapter introduces both general aspects of sample preparation and the main problems encountered in automating sample treatments. The second provides a brief discussion of the underexploited potential of freeze-drying for delivering samples in forms that facilitate their subsequent analysis. Chapter 3 is devoted to a kind of energy that has also received inadequate attention from analysts ultrasounds. 

In summary, DSC is a rapid technique and can be automated but requires a significant financial outlay for the equipment and does not provide T values for all samples under consideration for freeze-drying. 

This chapter does not deal with the electronic soft- and hardware to document the data, to calculate the desired results, and to monitor failures. The hardware is available in different configurations and the software can be bought or developed to fit into the software used in production. The prerequisites discussed are those for the methods of measurements and the plant layout to permit automation. The general prerequisite is the use of the same freeze-drying methods from product development through pilot plant studies to production for example, the same principle of temperature and pressure measurements, identical definitions of tolerances, and similar criteria for statistical evaluations. If this prerequisite is not observed, the development steps may have to be repeated to permit later automation. 

The uniformity of the quality of a product in different vials in one charge and the reproducibility between charges are the criteria for efficient production. This section deals therefore with the uniformity of one charge and the reproducibility of different charges in automated processes. The uniform freezing and freeze-drying are mainly influenced by (1) the correct situation of the stopper in the filled vial, (2) the bottom form of the vial (not the glass thickness), (3) the heat transfer from the brine in the shelves to the... 

P Haseley, GW Oetjen. Freeze-drying with automated control of residual moisture in model substances and in human albumin products for subsequent viral inactivation. Symposium on the Freeze-drying of Pharmaceuticals and Biologicals, Center for Pharmeceutical Processing Research, Breckenridge,... 

Other fire protection features have been incorporated into CNG refueling facilities such as methane detectors to warn of leaks from the dispenser, and automated fire suppression systems activated by ultraviolet/infrared detectors. Dry chemical is the preferred fire suppression material since water line protection from freezing is difficult in outdoor settings. The methane detectors can also be used to shut down the compressor and dispenser if desired. 

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