Freeze drying methods

The volatile fraction as defined by the various wet oxidation methods and most of the direct injection methods would be that fraction removed by acidification and purging with inert gas at room temperature. In the freeze-drying method of Gordon and Sutcliffe [29] the volatile fraction is that fraction lost by sublimation in vacuo. There have been no actual determinations of these losses, and for the most part Skopintsev s numbers were accepted as valid for all of these methods, largely because they are the only numbers available. 

Nagai, M., Nishino, T. II Aluminia ceramics fabricated by the spray-froze/freeze-drying method. International Institute of Refrigeration (Com. Cl, p. 186-190, Tokyo, 1985... 

Finally, radiochemical methods of analysis may be used to follow rates of detritiation. This method is particularly useful for very slow reactions (where it is impractical to collect data for any appreciable extent of reaction) as an initial rate approach may then be employed. Separation difficulties, at least for aqueous solutions, may be overcome by using the freeze-drying method or the more recent countercurrent dialysis and Sephadex gel filtration techniques. ... 

Natural penicillin is fragile and breaks down in the presence of impurities and enzymes, having a half-life of just 2.5 h even when cooled to 0 °C. The method of choice for stabilizing penicillin for storage and shipment turned out to be the freeze-drying method. Penicillin is frozen in trays at —30 °C it is then placed in a chamber at a pressure of 0.1-0.6 Torr to sublimate the ice crystals into water vapor and removed. 

Other semi-2-IPNs [52] processed by the freeze-drying method included IPN from 4,4 -bismaleimido diphenylmethane (BMI) and linear BTDA/3,4 -ODA polyamic acid that were dissolved in 1,3,5-trioxane (Fig. 16). The resulting semi-2-IPNs exhibited higher Tgs and reduced phase separation, and contained no plasticizing solvent. A comparison of unidirectional properties of composites prepared by the freeze-dry process to those by traditional solvent evaporation process is presented in Table 13. The freeze-drying method for the preparation of IPNs appears to be superior to previous technology. 

Kimura, Y., Ito, T.,Yoshikawa, H., Tachiwaki, T., Hiraki, A. Growth and characterization of homogeneous yttrium-barium-copper oxide (YBa2Cu307 6) powders prepared by freeze-drying method. Jpn. J. Appl. Pltys., Part 2 29,... 

Kondou, S., Kakojawo, K., Sasaki, Y. Synthesis of PbfZpJTij J03 by freeze drying method. Nippon Kagaku Kaishi (7), 753-758,1990... 

B. Optimization of Eutectic Crystaliine Freeze-Drying Method at Small Scale... 

Peak levels of the drug were observed at 4-6 h postadministration in the cases of the solid dispersion systems. In the case of dicumarol crystal powder, peak levels were observed at 2 to 12 hours postadministration. Average AUC values (0 8 h) of dicumarol following the administration of the dicumarol-PVP solid dispersion systems were 3.31 times (coevaporation method) and 1.54 times (freeze-drying method) that of control. The corresponding numbers for p-cyclodextrin dispersions were 2.18 and 1.72. 

Another approach to a total combustion is the freeze-drying method of Gordon and Sutcliffe (34). In this method, the seawater sample is acidified with phosphoric acid and taken to dryness in a freeze-drier. The resulting sea salts are analyzed in a commercial C-H-N analyzer. The results obtained by this method are higher than those of Sharp (27) and agree quite well with those of Skopintsev and Timofeyeva (10). Again,... 

Shortly after we had run this comparison study, our own aged freeze-drier collapsed into obsolescence. In order to make this method work, the freeze-drier must be specially constructed, without resin in the vacuum chamber and with traps placed in the vacuum line to prevent the back-diffusion of oil vapors from the pump to the vacuum chamber. While we have been awaiting the rejuvenation of our own instrument, rebuilt to these specifications, Michael McKinnon, of our laboratory, has developed a variation of the Russian evaporation method. In this method, as in the freeze-drying method, the great problem is avoiding contamination. Fortimately, when contamination does occur, it seems to affect an entire batch of samples. It is therefore possible to detect the contamination by the judicious use of standards. This method gives values for DOG of the same order as the lowest freeze-drying values or the Sharp (27) direct injection values. 

We still do not have a referee method for DOC. The resolution of the disagreement between the various total combustion methods has yet to be accomplished. Probably we will find that the Sharp (27)-direct injection and the Gordon and Sutcliffe (34)-freeze-drying methods are measuring the same quantities once the problem of contamination is solved, and it will be the difference between their values and those of the Russians which has to be resolved. 

The freeze-drying method is one of solvent volatilization, but it differs from the common solvent evaporation techniques in that the solvent is sublimed from the solid state. A solution, prepared by means of soluble salts or by dissolving metals in acid, is frozen and the solid solvent, usually water in the form of ice, is sublimed away giving the dried salts. The process gives high surface area powders of excellent chemical homogeneity. 

The two purified components, component I and component II (the stability and storage of trypsinized component II will be described below), are relatively stable proteins and can be stored in the freezer (at -20 °C) for at least 3 months without loss of their activities, if freezing and thawing are not repeated too frequently. To store them for longer periods, however, it is preferable to freeze-dry and keep them in a deep freezer (-80 °C) in a desiccator both components are stable under the conditions for normal freeze-drying method without any additives. 

Ultrasound-Responsive Liposomal Preparation by Freeze-Drying Method... 

The freeze-drying method uses sublimation (solid to vapor transformation) to dry specimens. This method requires freezing a specimen rapidly to below —80°C in a chamber. At that temperature, the chamber is degassed under a low pressure of below 0.1 Pa. The specimen can be dried in such a condition after several hours to several days. 

Controlled-release biodegradable PLG polymers loaded with parathyroid hormone were formulated as a freeze-dried form with particle size ranging from 27 to 47 i. The freeze-dried method did not alter the surface morphology, particle size, and parathyroid hormone content or release rate of the microspheres. The freeze-dried microspheres resuspended very rapidly and uniformly in solution. In vitro release studies indicated that except for a slight early burst ranging from 4-18%, release of parathyroid hormone from the nanoparticles was very slow over the first 14 days. At 15 days, release of parathyroid hormone accelerated rapidly. 

Monophasic Ln x MnOs (Ln = La, Nd) perovskites with high surface areas (8-27 m /g) were synthesised at mild conditions by the freeze-drying method, and were found to be active for the catalytic combustion of ethane at low temperatures (573 to 648 K). As a general troid, the substitution of the rare earth cation by potassium decreased the intrinsic activity, reduced the reaction order in oxygen and, for the more substituted samples (x>0.10), it increased the selectivity to ethene. It was found that the rare earth cation also influenced the catafytic activity of the substituted perovskites. These effects were analysed in terms of structural modifications induced by the introduction of potassium in the perovskites. 

Catalytic asymmetric cyanation using 20 mol % of the complex of Ti(Oz-Pr)4 with diisoporpyl tartrate (10 Fig. 1) was reported by Oguni [42,43]. The mixture of Ti(Oi-Pr)4 and 10 (Fig. l)did not exhibit high enantioselectivity. Moreover, the selectivity and the reactivity were still low when the formed isopropyl alcho-hol was removed under reduced pressure using the freeze-dry method. High reactivity and an enantioselectivity of up to 90% were observed when the isopropyl alcohol was again added to the freeze-dried titanium complex. 

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