Physicochemical properties of drugs in solution

however, we recount the various ways to express the strength of a solution, since it is of fundamental importance that we are able to interpret the various units used to denote solution concentration and to understand their interrelationships, not least in practice situations. 

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Orally administered dosage forms are absorbed into the systemic circulation following dissolution in the GI tract. Because substances must be in solution for the absorption from the GI lumen, the absorption rate of poorly water-soluble drugs is limited by their rate of dissolution. The dissolution rate is affected by the unique physicochemical properties of the drug and by physiological factors the pH, composition, and hydrodynamics of the GI medium. 

There are a number of physicochemical properties of an API that are impacted upon size reduction, which need to be considered while resolving pharmaceutical problems related to solubility limitations. Clearly, dissolution rate and its dependence upon particle size reduction is one of those critical properties (Ross and Morrison, 1988 Rabinow, 2004 Kocbek et al., 2006). For example, in the case of oral administration of a poorly water-soluble API, the increase in dissolution rate attendant with size reduction provides for more drug in solution, and available for absorption, during its gastrointestinal transit (Chaumeil, 1998 Merisko-Liversidge et al., 2003 Patravale et al., 2004 Pouton, 2006). 

The final stage of the residue analysis procedures involves the chromatographic separation and instrumental determination. Where chromatographic properties of some food residues are affected by sample matrix, calibration solutions should be prepared in sample matrix. The choice of instrument depends on the physicochemical properties of the analyte(s) and the sensitivity required. As the majority of residues are relatively volatile, GC has proved to be an excellent technique for pesticides and drug residues determination and is by far the most widely used. Thermal conductivity, flame ionization, and, in certain applications, electron capture and nitrogen phosphorus detectors (NPD) were popular in GC analysis. In current residue GC methods, the universality, selectivity, and specificity of the mass spectrometer (MS) in combination with electron-impact ionization (El) is by far preferred. 

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