Ionic Equilibria and pH

Ionic Equilibria and pH reviews the quantitative aspects of aqueous acid-base chemistry. Definitions and concepts are presented and appropriate worked examples illustrate calculations of concentration, pH and ionization constants. Acid-base properties of salts (salt hydrolysis) is introduced and explained along with the common-ion effect and calculation of hydrolysis constants. Equilibria of acid-base buffers with respect to buffer preparation, calculating the pH of a buffer solution and application of the Henderson-Hasselbalch equation, buffer range and buffer capacity is discussed. Determining the pH during acid-base titrations, selecting the appropriate acid-base indicators, and generating pH titration curves are explained.

Solubility and Partition Coefficient of Salicylamide in Various pH Buffer Solutions

The solubility and partition coefficient are essential physicochemical parameters in developing a pharmaceutical dosage form of medicine. In addition, these parameters help to predict the absorption of an active compound in oral or topical dosage forms. Salicylamide, an active ingredient available in oral and topical dosage forms, is a weak acid (pKa 8.2) and is sparingly soluble in water. Meanwhile, its solubility and partition coefficients are influenced by the pH of the environment. The Henderson-Hasselbalch equation is used to predict solubility-pH and partition-pH profiles at various pH solutions. This study aims to determine salicylamide's solubility and partition coefficient in various pH (2–11). Both tests were carried out in various pH buffer solutions (at a concentration of 0.02 M and 0.2 ionic strength) in a water bath shaker at a temperature of 37 ± 0.5 °C. In addition, the salicylamide content was determined using the UV spectrophotometer method at the maximum wavelength at each pH. The results showed that the solubility increased at pH 2–10, while the partition coefficient value decreased. On the other hand, at pH 11, there was an increase in the number of ionized species, but the solubility decreased.

A primer on tissue pH and local anesthetic potency

The relationship between pH, p Ka, and degree of local anesthetic ionization is quantified by the Henderson-Hasselbalch equation. As presented in standard textbooks, the effect of pH on the degree of ionization of any particular local anesthetic is not immediately clear due to the x-axis displaying pH − p Ka, which requires conversion to pH, based on the p Ka for each local anesthetic, a complex process. We present a graphical solution that clarifies the interrelationships between pH, p Ka, and degree of ionization by plotting p Ka on the x-axis versus the percentage of unionized local anesthetic on the y-axis. The vertical intercept from the x-axis to the pH curves allows rapid and accurate estimation of the degree of ionization of any local anesthetic of known p Ka.

Prompt Rise in Urinary Ammonium Excretion Suffices To Mitigate Metabolic Acidosis in an Experimental Animal Model of Severe Normovolemic Hemodilution

Recently, we have established a model of severe stepwise normovolemic hemodilution to a hematocrit of 10 % in rats employing three different colloidal volume replacement solutions (Voluven, Volulyte and Gelafundin) that are routinely used in clinical practice at present. We did not see severe dilutional acidosis as to be expected, but a decline in urinary pH. We here looked on further mechanisms of renal acid excretion during normovolemic hemodilution. Bicarbonate, which had been removed during normovolemic hemodilution, was calculated with the help of the Henderson-Hasselbalch equation. The urinary amount of ammonium as well as phosphate was determined in residual probes. The absolute amount of free protons in urine was obtained from the pH of the respective samples. The amount of protons generated during normovolemic hemodilution was approximately 0.6 mmol. During experimental time (5.5 h), distinct urinary ammonium excretion occurred (Voluven 0.52 mmol, Volulyte 0.39 mmol and Gelafundin 0.77 mmol). Proton excretion via the phosphate buffer constituted 0.04 mmol in every experimental group. Excretion of free protons was in the range of 10-6 mmol. The present data prove that the prompt rise in urinary ammonium excretion is also valid for acute metabolic acidosis originating from severe normovolemic hemodilution.

Acute Kidney Injury

Simple acid-base disorders are defined by changes in pH and the initial change in 1 of the 2 variables, serum bicarbonate (HCO3-) and PCO2. Low pH indicates acidosis, and high pH indicates alkalosis. If 1 of the 2 components (HCO3-or PCO2) decreases, the other component also decreases (a compensatory change that minimizes the change in the ratio and the pH) and vice versa, as shown in the Henderson-Hasselbalch equation. Emphasis has been placed on the Henderson-Hasselbalch equation because the equation describes the 4 acid-base disorders and their compensatory changes.