Base/acid ratio

The general manufacturing scheme for phosphate salts is shown in Figure 11. Condensed phosphates are prepared from the appropriate orthophosphate or mixture of orthophosphates, so the preparation of orthophosphates must be considered first for the manufacture of any phosphate salt. Phosphoric acid is neutralized to form a solution or slurry with a carefully adjusted acid/base ratio according to the desired orthophosphate product. The orthophosphate may be recovered either by crystallization from solution, or the entire solution or slurry may be evaporated to dryness. The dewatering (qv) method is determined by the solubihty properties of the product and by its desired physical properties such as crystal size and shape, bulk density, and surface area. Acid orthophosphate salts may be converted to condensed phosphates by thermal dehydration (calcination). 

Fig. 2-12. The effect of the acid/ base ratio on the selectivity of sotalol on teicoplanin CSP (250 x 4.6 mm) in the new polar organic mode. The flow rate was 1.0 mL min at ambient temperature (23 °C).

An example of the effect of acid and base concentration on the separation of propranolol is shown in Fig. 2-13. In this case, the baseline separation is achieved by adjusting the concentration without changing the acid/base ratio. 

The buffer range is the pH range over which the buffer is effective. It is related to the ratio of concentrations of the weak acid and its conjugate. The further the ratio is from 1, the less effective the buffering action. Ideally, the acid/base ratio should be between 0.1 and 10. Since log10 10 = 1 and log10 0.1 = — 1, buffers are most useful within 1 pH unit of the weak acid s pfQ. 

A buffered solution may contain a weak acid and its salt, e.g. acetic acid and acetate ion, or a weak base and its salt, e.g. NH3 and NH4CI. By choosing the appropriate components, a solution can be buffered at virtually any pH. The pH of a buffered solution depends on the ratio of the concentrations of buffering components. When the ratio is least affected by adding acids or bases, the solution is most resistant to a change in pH. It is more effective when the acid-base ratio is equal to unity. The pK of the weak acid selected for the buffer should be as close as possible to the desired pH, because it follows the following equation ... 

The presence of triethylamine in the aqueous portion of the mobile phase was shown to be important for the separation of enantiomers of /-Boc-amino acids, whereasa native amino acids were almost not affected by the addition of TEAA [34]. Lee and Beesley [48] observed that a change in the ionic interactions occurred when changing the acid/base ratio in reversed and polar organic mobile phases or changing the buffer pH in the reversed-phase mode. Consequently, the retention, selectivity, and peak shape is affected. 

A number of factors other than the solvent can affect the stereoselectivity of deprotonation of esters, such as the acid-base ratio and the nature of the base. But selective formation of (E)-silyl ketene acetals from esters remains a problem, particularly since they are more reactive than the (Z)-isomers. 

Some degradation products are either very polar or very nonpolar in nature this may present an issue in chromatography, where they may not be retained or strongly adsorbed on the column, respectively. One may also want to double check the reference standard for its purity, moisture content, and/or salt/ acid-base ratio for calculation. An analytical chemist must remember to explore all possibilities if mass balance issue is observed (either during method development, validation and/or stability testing). 

In solvents of low dielectric constant, difficulties arise in the determination of the protolysis constants as lack of knowledge of the species present makes uncertain the calculation of the acid-base ratio. In aprotic solvents the solvent does not participate in the acid-base equilibrium, and it is necessary to have a second acid-base system to exhibit the acidity function. In the absence of a solvent, hydrogen chloride reacts with aniline as follows ... 

This procedure has been repeated in our laboratory and in production (modified version) hundreds of times, and the average for 1993 activity/acid-base ratio was 96%, with a standard deviation of 2%. This indicates that, if the proper procedure is followed, then a reproducible yield of Grignard reagent can be attained. The most common variation on this preparation is the type of Mg activation (see Chapter 4). Other recommended preparations can be found within this book (see especially Chapters 3 and 4) and in the literature [continuous process Ref. 41 and batch process Refs. 42, 43]. 

The work described in the foregoing sections is of a preliminary nature. Nevertheless, it offers hope that experimental scales of free hydrogen ion concentration (pcn or pmn) in seawater may be feasible. One need not know pmn or pan to derive meaningful equilibrium data, such as acid-base ratios and solubilities, provided that suitable apparent equilibrium constants are chosen (7). In these cases, the unit selected for the acidity scale disappears by cancellation. Nevertheless, the acidity of seawater is a parameter of broader impact. It plays a role, for example, in the kinetics of organic oxidation-reduction reactions and in a variety of quasi-equilibrium processes of a biological nature. The concentration of free hydrogen ions is clearly understood, and its role in these complex interactions is more clearly defined than that of a quantity whose unit purports to involve the concept of a single-ion activity. 

Control of pH is vital in synthetic and analytical chemistry, just as it is in living organisms. Procedures that work well at a pH of 5 may fail when the concentration of hydronium ion in the solution is raised tenfold to make the pH 4. Fortunately, it is possible to prepare buffer solutions that maintain the pH close to any desired value by the proper choice of a weak acid and the ratio of its concentration to that of its conjugate base. Let s see how to choose the best conjugate acid-base system and how to calculate the required acid-base ratio. 

It should be noted, however, that the distinction between the two strategies is only instrumental to the discussion, since intermediate situations whereby homoionic and heteroionic hydrogen-bonding interactions may co-exist, for example, and —0 can be obtained by means of a large acid base ratio. 

A much better basis than depression of the respiratory center for the explanation of the carbon dioxide retention is the increase in alkaline reserve (1). If one assumes that the body attempts to maintain a constant pH and that the body is still partially successful in this attempt after the administration of morphine, an increase in base must lead to a retention of carbon dioxide to neutralize the base and a further retention to keep the acid-base ratio constant. 

In the region of the titration curve in which the pH changes very little upon addition of acid or hase, the acid/base ratio varies within a narrow range (10 1 at one extreme and 1 10 at the other extreme). 

When adjusting for pH effect on h. it should be noted that the hydrogen ion concentration, in addition to being a component of the mass action expression, can affect the acid/base ratio. For example, in the following H2S system ... 

The answer is B. This is actually one way of defining pKa value. At the pKa value, the acid-base ratio is 1. So the best answer is Choice B. In addition, it is near the pKa value that the solution will have its best buffering capacity. So Choice D wrong. 

Graph of Resolution against Acid Base Concentration (Acid/Base Ratio 1 1)... 

The resemblance of this ratio to a monoprotic acid-base ratio can be seen by comparison of equation (12-7) with... 

The solution contains a reservoir of base that consumes the added acid, and a reservoir of acid to consume added base. In each case, the acid-base ratio is changed, but with only a moderate effect on the pH of the solution. Very little of the H+ or OH added will remain as such. The following example illustrates the quantitative treatment of buffer action. 

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