Dynamic vapor sorption

The formation of niclosamide hydrates, and the effect of relative humidity on the solvatomorphs obtained from acetone and ethyl acetate has been studied [79], The acetone and ethyl acetate solvatomorphs could be desolvated, and exposure to elevated humidity resulted in the formation of two hydrate structures. Each hydrate could be dehydrated into a different anhydrate phase, but only the hydrate formed from the acetone desolvate could be rehydrated to form a hydrate phase. Dynamic vapor sorption has been used to develop a method for determining the onset relative humidity of a glass transition and associated crystallization process [80]. 

Teoh, H.M., Schmidt, SJ., Day, G.A., and Faller, J.F. 2001. Investigation of commeal components using dynamic vapor sorption and differential scanning calorimetry. J. Food Sci. 66, 434-440. Tromp, R.H., Parker, R., and Ring, S.G. 1997. Water diffusion in glasses of carbohydrates. Carbo-hydr. Res. 303, 199-205. 

There are many examples of second-order analyzers that are used in analytical chemistry including many hyphenated spectroscopic tools such as FTIR-TGA, IR-microscopy, as well as GC-MS, or even two-dimensional spectroscopic techniques. Another hyphenated technique that is being developed for the study of solid-state transitions in crystalline materials is dynamic vapor sorption coupled with NIR spectroscopy (DVS-NIR).26 DVS is a water sorption balance by which the weight of a sample is carefully monitored during exposure to defined temperature and humidity. It can be used to study the stability of materials, and in this case has been used to induce solid-state transitions in anhydrous theophylline. By interfacing an NIR spectrometer with a fiber-optic probe to the DVS, the transitions of the theophylline can be monitored spectroscopically. The DVS-NIR has proven to be a useful tool in the study of the solid-state transitions of theophylline. It has been used to identify a transition that exists in the conversion of the anhydrous form to the hydrate during the course of water sorption. 

Water sorption-desorption isotherms can be carried out by using thermobalances. Now specific instruments allow to measure water sorption-desorption isotherms at different constant temperatures (e.g., dynamic vapor sorption instrument (DVS), Surface Measurement Systems Ltd., Monarch Beach, US). 

Measured using Dynamic Vapor Sorption, Sudzucker AG. 

There are several advantages to the dynamic vapor sorption device. First, any humidity value can be dialed in, whereas salt solutions are not available for every humidity value and some are quite toxic. Second, since the weight is monitored as a function of time, it is clear when equilibrium is reached. The dynamic devices also give the sorption/desorption rates, although these can easily be misused (see the drying kinetics section later). The salt solution method, on... 

A relatively fast and less labor-intensive process is the dynamic vapor sorption method. In this automated process, the sample is placed on a microbalance within the environment of a given relative humidity at a constant temperature. The relative humidity is changed continuously with a device controlled by a computer. The change in sample weight is monitored as a function of time or as a function of relative humidity, and the event is recorded. The weight gained (adsorption) or weight lost (desorption) versus relative humidity may... 

In the preformulation study, the comprehension of physicochemical properties regarding water-solid surface interaction is beneficial to the handling, formulation, and manufacture of the finished products. Data on sorption/de-sorption isotherm, hydration of salts of drug product, water sorption of pharmaceutical excipients, and kinetics of water adsorption or desorption of a substance can be obtained effectively by the dynamic vapor sorption method. The knowledge may be utilized for dosage form design and supports the understanding of the mechanism of action. 

Figure 1 The dynamic vapor sorption chart for microcrystalline cellulose. The percentage mass change is based on a 10-mg sample of microcrystalline cellulose reference material. Steps refer to relative humidity changes. Source Courtesy of Surface Measurement Systems (1).

Figure 7.1 The dynamic vapor sorption chart for microcrystalline cellulose.

Water vapor sorption (WVS) is used to assess the hygroscopicity of the hot melt extruded formulations. WVS is used in quantification of amorphous content in pharmaceutical solids. Prodduturi et al. investigated the use of rapid dynamic vapor sorption techniques for analysis of films containing hydroxypropyl cellulose and clotrimazole. ... 

Penner EA (2013) Comparison of the new vapor sorption analyzer to the traditional saturated salt slurry method and the dynamic vapor sorption instrument. M. Sc. dissertation, University of Illinois... 

A practically very useful method to investigate hydrates is dynamic vapor sorption (DVS) (see Section 8.2.3.2). It provides information on the water sorption behavior of substances, and while it is less suited than slurry experiments to obtain thermodynamic parameters of hydrates, it provides very valuable kinetic information. 

Dynamic vapor sorption (DVS) (sometimes also called gravimetric vapor sorption (GVS)) is a suitable method to investigate hydrate formation and hygroscopidty. In a... 

Moreover, isopiestic water sorption data and dynamic vapor sorption (Soboleva et al., 2011) provide information on water uptake as a function of relative humidity in the surrounding gas phase. This information, if combined with pore size distribution data, could help determine the wetting angle in pores or the Gibbs energy of water sorption as functions of pore size. 

Dynamic vapor sorption kinetics and isotherms. Different vapor concentrations were generated with gravimetrically calibrated vapor diffusion tubes at 25 C under constant flow of carrier gas (15 ml/min helium). Vapor concentrations were adjusted by dilution with a second computer controlled helium flow (0-200 ml/min). Sorption measurements were carried out similar to those described above for nitrogen. Equilibrium was usually assumed and the next partial pressure was adjusted when the frequency change of the QCM was less than 1 Hz in 90 seconds. The close coincidence of adsorption and desorption branches of many isotherms shows that the measurements are ofen close to true equilibrium. 

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