Drying from solutions discussion

Disordered conformation. Figure 5 shows electron micrographs of xanthan D and F obtained from xanthan vacuum-dried from solutions yielding the disordered conformation. The various molecular assemblies are assigned as follow I = single -stranded, II = perfectly matched double stranded, III = branched from double - to single stranded. This assignment will be discussed below. 

The dry surface chemistry, i.e. chemistry of solid-gas interfaces has its own methodology and language. A substantial difference between wet and dry surface chemistry is that adsorption from solution is always an exchange, the empty surface is in fact occupied by solvent. In spite of an obvious relationship between dry and wet surfaces, only wet surface chemistry will be discussed here, although some quantities (e.g. the BET surface area) and relationships involve results obtained for dry surfaces. In particular, certain adsorbates considered show substantial vapor pressure at room temperature, and sorption of their vapors has been studied. Such results, albeit related to sorption of the same species from aqueous solution are beyond the scope of the book. 

The phenomena presented in this book were discussed in many reviews. For example, Schwarz [13] discussed methods used to characterize the acid base properties of catalysts. The review on sorption on solid - aqueous solution interface by Parks [14] includes also principles of surface science. The book Environmental Chemistry of Aluminum edited by Sposito reviews the solution and surface chemistry of aluminum compounds. Chapter 3 [15] provides thermochemical data for aluminum compounds. Chapter 5 [16] lists the points of zero charge of aluminum oxides, oxohydroxides and hydroxides with many references on adsorption of metal cations and various anions on these materials. Unlike the present book, which is confined to sorption from solution at room temperature, publications on coprecipitation and adsorption from gas phase or at elevated temperatures are also cited there. Brown et al. [17] reviewed on dry and wet surface chemistry of metal oxides. Stumm [18] reviewed sorption of ions on iron and aluminum oxides. The review by Schindler and Stumm [19] is devoted to surface charging and specific adsorption on oxides. Schindler [19] published a review on similar topic in German. Many other reviews related to specific topics are cited in respective chapters. 

In the US, two separate guidelines have been developed, one covering both metered dose inhalers (MDIs) and dry powder inhalers (DPIs) and one covering nasal sprays, inhalation solutions, and suspensions and inhalation sprays [22, 23], The guidance on MDIs and DPIs is however still in draft form nearly 10 years after being published for comment one of the unresolved issues is the dose content uniformity requirements which are discussed later in this chapter (Section 16.5.4). There are also other sections which would benefit from further discussion, in particular the number and nature of some of the tests that may be expected on stability. 

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