Moisture transfer

JH Bell, NA Stevenson, JE Taylor. A moisture transfer effect in hard gelatin capsules of sodium cromoglycate. J Pharm Pharmacol 25 (suppl) 96P-103P, 1973. 

G Zografi, GP Grandolfi, MJ Kontny, DW Mendenhall. Prediction of moisture transfer in mixtures of solids transfer via the vapor phase. Int J Pharm 42 77-88, 1988. 

Water is introduced into closed pharmaceutical systems either accompanying the input materials or in the headspace as relative humidity [79]. Whatever water is contained within the dosage form and its container will ultimately equilibrate among the components according to its affinity for the solid ingredients and the number of association sites. The Sorption-Desorption Moisture Transfer model has been used to evaluate the thermodynamically favored state that will result after the equilibration process is complete [79]. 

Combining solids that have previously been equilibrated at different relative humidities results in a system that is thermodynamically unstable, since there will be a tendency for moisture to distribute in the system so that a single relative humidity is attained in the headspace. As shown in Fig. 7, moisture will desorb into the headspace from the component initially equilibrated at a higher relative humidity and sorb to the component initially equilibrated at a lower relative humidity. This process will continue until both solids have equilibrated at the final relative humidity. The final relative humidity can be predicted a priori by the sorption-desorption moisture transfer (SDMT) model [95] if one has moisture uptake isotherms for each of the solid components, their initial moisture contents and dry weights, headspace volume, and temperature. Final moisture contents for each solid can then easily be estimated from the isotherms for the respective solids. 

Fig. 7 Schematic representation of moisture transfer between solid components A and B with (a) headspaces isolated from one another and (b) headspaces allowed to equilibrate. Ra and Rb = initial relative humidities above A and B VA and VB = headspace volumes above A and B Rf and VT = final relative humidity and headspace volume above A and B. (From Ref. 95.)...

Pikal, M. J., Shah, S. Moisture transfer from stopper to product and resulting stability implications. Developments in Biological Standardization Vol. 74, 1991, p. 165-179. Acting Editors Joan C. May, F. Brown, S. Karger AG, CH-4009 Basel (Switzerland), 1992... 

Nieto, A., Castro, M.A., and Alzamora, S.M. 2001. Kinetics of moisture transfer during air drying of blanched and/or osmotically dehydrated mango. J. Food Engineer. 50, 175-185. 

Moisture. Transfer an accurately weighed portion of approx 1 g of the flash charge compn to a tared moisture dish 2 inches in diameter. Place the moisture dish and contents in a drying oven at 80°—85 °C for 2 hours, cool in a desiccator and weigh. Calculate the loss in weight of die dish and contents to percent moisture in die sample... 

Determination of Moisture. Transfer to a fared glass weighing dish a portion of approx 2 grams (g) of the sample and weigh accurately. Dry the dish and contents at 100°C to 105°C for 1 hr, cool in a desiccator and weigh. Calculate the loss in weight and percent of moisture... 

Veillard, M., Bentejac, R., Duchene, D., and Carstensen, J. T. (1979), Moisture transfer tests in blister package testing, Drug Dev. Ind. Pharm. 5,227-244. 

Badway, S. I. F., Gawronski, A. J., and Alvarez, F. J. (2001), Application of sorption-desorption moisture transfer modeling to the study of chemical stability of a moisture sensitive drug product in different packaging configurations, Int. J. Pharm., 223(1-2), 1-13. 

In one operational mode, the system pw is established by a large sample and is characterized by the sensor. The amount of moisture transfer from the sample does not significantly change its moisture content. The sensor is queried to identify its condition, and the result is converted into an estimation of pw. 

Place sample (5 to 10 ml) in a disposable sample cup, completely covering the bottom of the cup, if possible. Place sample into sample cup in a timely manner to minimize moisture loss or gain during handling. If sample is not to be tested immediately, place a sample cup lid on the cup to prevent moisture transfer with the room atmosphere. 

The relative amounts of sample and standard material have to be different because the moisture transferred from the food sample to the standard (characterized by the mass gain of the standard) must not result in a significant change in the vapor pressure maintained by the sample. Essentially, the sample replaces the salt solution in the Basic Protocol to create constant aw in the closed chamber. 

In trying to formulate DMP-754, Badway et al. (51) investigated binary blends as well as compacts of DMP-754 (Fig. 2) with anhydrous lactose and concluded that compaction of the blends resulted in an increase in the amount of hydrolysis seen (Table 5). Badway et al. postulated that this result was due to an increase in the number of contact points between the drug and the lactose resulting in an increased rate of moisture transfer leading to degradation. 

De Rosnay et al. (2000) assessed the reliability of schemes that parameterize land surface processes to find the correspondence between calculated mean annual fluxes of energy and moisture depending on detailed consideration of the vertical structure of soil. These schemes are used in general circulation models of the atmosphere (GCMAs). The calculations testify to the strong dependence of fluxes on vertical resolution. The 11-layer scheme parameterizing heat and moisture transfer in the top 1 mm thick layer of soil was found to be adequate. 

The simplest technique is to use separate numerical solvers for the fluid and solid phases and to exchange information through the boundary conditions. The use of separate solvers allows a flexible gridding inside the solid phase, which is required because of the three orders of magnitude difference in thermal conductivities between the solid and gas. It is also easy to include various physical phenomena such as charring and moisture transfer. Quite often, ID solution of the heat conduction equation on each wall cell is sufficiently accurate. This technique is implemented as an internal subroutine in FDS. 

In all the following operations, an atmosphere of prepurified nitrogen must be maintained throughout the reaction, and all glassware must be flame-dried or oven-dried and purged with nitrogen to remove traces of moisture. Transferals of molyb-... 

Cenco-Fitch Heat transfer apparatus Thermal moisture tester Rate of heating Heat flux Rate of heat and moisture transfer... 

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