Acidity, pH and

Only acids are sour. Sourness is not identical to chemical acidity or pH, which is a function of the hydrogen ion concentration, but also appears to be a function of the entire acid molecule. A combination of pH and acid concentration determines the actual degree of the sour taste. At the same pH, any organic acid, eg, citric acid, exhibits a far greater sourness than a mineral acid, eg, hydrochloric acid (27,28). 

Acid leaks that cause problems of fluctuating pH and acid corrosion. 

Friedman AL, Brittain D, Menon L (2007) Roles of pH and acid type in the anodic growth of porous alumina. J Chem Phys 127 154717-154723... 

Romero, C. and Bakker, J., Interactions between grape anthocyanins and pyruvic acid, with effect of pH and acid concentration on anthocyanin composition and color in model solutions, J. Agric. Food Chem., 47, 3130, 1999. 

Buffering the mobile phase with appropriate buffer solution will result in the sole AH as chemical species. In this mode we can easily use RPLC (provided the phase will stand the pH ), and acids are eluted according to their hydrophobicity. 

As mentioned earlier, understanding the pH equation and the regulation and control of pH is fundamentally important when considering very many life and health processes. A simple indication of the importance of environmental pH is for growth of crops (soil pH) and acid rain (water pH), which can affect the ecosystem. Indeed, optimum conditions for purification of water and sewage treatment also are pH dependent. Physiologically, pH is critical to maintain normal body functions and key to biochemical reactions in the blood and other body fluids. Buffers and buffer systems are the primary means to regulate and maintain pH, and are discussed in more detail below (with examples in Appendix 3). 

LoBrutto, R. et al. Effect of the eluent pH and acidic modifiers in high-performance liquid chromatography retention of basic analytes. J. Chromatogr. A. 2001, 913, 173-187. 

Munson R. K. and Gherini S. A. (1993) Influence of organic acids on the pH and acid-neutralizing capacity of Adirondack lakes. Water Resour. Res. 29, 891-899. 

A kinetic study of the photohydroxylation of the quinone (371) in potassium hydroxide and perchloric acid solution, has been reported. The phototautomerism of the quinone (372) has been studied and the effect of pH and acidity evaluated. - ... 

There have been many attempts to investigate the effect of extractives on cure chemistry and bonding to wood (33-35). For example, the effect of extractives from pressure-refined hardwood fiber on urea-formaldehyde resin was studied (34, 35) and it was found that the ethanol-soluble extractives decreased the gel time as much as 41%, and the sequentially extracted water-soluble extractives increased the gel time in excess of 65%. There was little correlation between the extractive content and gel time however, an empirical relation between the pH of the extractives and the gel time was observed (35). The effect of several species of wood on the gel time of urea-formaldehyde resin have also been studied (36). In these studies the gel time was correlated with the pH and acid buffering capacity of the extract. 

Buchanan, R.L., Edelson-Mammel, S.G., Boyd, G., and Marmer, B.S. 2004. Influence of acidulant identity on the effects of pH and acid resistance on the radiation resistance of Escherichia coli 0157 H7. Food Microbiology 21 51-57. 

Food preservation has for a long time employed a combination of factors in which acids have played an important role (Knochel and Gould, 1995). It is, therefore, of great interest to effectively apply the combined effects of several factors that inflict obstructions to the growth of microbes (Chirife and Favetto, 1992). Studies on a specific organism, and inclusion of several factors, such as water activity, temperature, pH, and acid concentration, have often been carried out in model systems, and mathematical models have been developed describing the behavior (Hsiao and Siebert, 1999). 

Fig. 23.6 Relationship between pH and acid dyes adsorbed by Nylon 66...

Romero, C. Bakker, J. Interactions between grape anthocyanins and pyruvic acid, with effect of pH and acid concentration on anthocyanin composition and color in model solutions. J. Agric. Food Chem. 1999, 47, 3130-3139. Mateus, N. Silva, A. M. S. Vercauteren, J. De Freitas, V. A. P. Occurrence of anthocyanin-derived pigments in red wines. J. Agric. Food Chem. 2001, 49,4836-4840. 

Firmness, Soluble Solids and Acidity Changes. During the postharvest ripening period, the changes in firmness, soluble solids, pH and acidity of kiwifruit at 20°C in the presence of 5 ppm ethylene gas are shown in Table I. 

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