Determination of Acid/Base Dissociation Constants Based on a Rapid Detection of the Half Equivalence Point by Feedback-Based Flow Ratiometry

One of the uses of acid-base indicators is to show the end point of the titration, so the accurate determination of acidity constant and pH range of indicators needs to be done. This study aims to determine the acidity constant (pKa) of mangosteen pericarp extract and its accuracy as an indicator of acid-base titration. Determination of pKa was done by a simple potentiometric titration method. The titration data were plotted in three graphs, i.e., pH, ΔpH/ΔV (the (the first derivative), and Δ2pH/ΔV2 (the second derivative) versus titrant volume to determine the equivalence point of the titration. The accuracy test was carried out by comparing the volume of oxalic acid used to titrate NaOH solution using the indicator of mangosteen pericarp extract and phenolphthalein indicator. The result showed that the equivalence point was found on the titrant volume of 8.6 mL and a measured pH of 9.84. so the pKa value of mangosteen pericarp extract was 7.20, and the pH range was 6.20 to 8.20. the average volume of oxalic acid used to titrate 5 mL of NaOH using phenolphthalein as the indicator was 5.2 mL while the titration used mangosteen pericarp extract was 5.23 mL. The accuracy of mangosteen pericarp extract was 99.42%. By the result, it can be concluded that potentiometric titration can be used as a simple way to determine the acidity constant of mangosteen pericarp extract. Moreover, the mangosteen pericarp extract can be used as an alternative acid-base titration indicator to substitute the common acid-base titration in the laboratory.

Download Full-text

Acid-Base Equilibria in Glacial Acetic Acid. III. Acidity Scale. Potentiometric Determination of Dissociation Constants of Acids, Bases and Salts1

Journal of the American Chemical Society ◽

10.1021/ja01594a014 ◽

1956 ◽

Vol 78 (13) ◽

pp. 2974-2979 ◽

Cited By ~ 83

Author(s):

S. Bruckenstein ◽

I. M. Kolthoff

Keyword(s):

Acetic Acid ◽

Glacial Acetic Acid ◽

Dissociation Constants ◽

Potentiometric Determination ◽

Acid Base ◽

Acidity Scale

Download Full-text

Determination of Chlorinity of Water without the Use of Chromate Indicator

International Journal of Analytical Chemistry ◽

10.1155/2010/602939 ◽

2010 ◽

Vol 2010 ◽

pp. 1-7 ◽

Cited By ~ 6

Author(s):

Tae-Kee Hong ◽

Myung-Hoon Kim ◽

Myung-Zoon Czae

Keyword(s):

Sea Water ◽

Sudden Change ◽

Weak Acid ◽

New Method ◽

Optimal Conditions ◽

Equivalence Point ◽

Acid Base ◽

Initial Ph ◽

Insoluble Salt

A new method for determining chlorinity of water was developed in order to improve the old method by alleviating the environmental problems associated with the toxic chromate. The method utilizes a mediator, a weak acid that can form an insoluble salt with the titrant. The mediator triggers a sudden change in pH at an equivalence point in a titration. Thus, the equivalence point can be determined either potentiometrically (using a pH meter) or simply with an acid-base indicator. Three nontoxic mediators (phosphate, EDTA, and sulfite) were tested, and optimal conditions for the sharpest pH changes were sought. A combination of phosphate (a mediator) and phenolphthalein (an indicator) was found to be the most successful. The choices of the initial pH and the concentration of the mediator are critical in this approach. The optimum concentration of the mediator isca.1~2 mM, and the optimum value of the initial pH isca.9 for phosphate/phenolphthalein system. The method was applied to a sample of sea water, and the results are compared with those from the conventional Mohr-Knudsen method. The new method yielded chlorinity of a sample of sea water of (17.58 ± 0.22) g/kg, which is about 2.5% higher than the value (17.12 ± 0.22) g/kg from the old method.

Download Full-text

EXPLORING OF ACID-BASIC PROPERTIES, DEVELOPMENT AND VALIDATION OF THE METHOD OF QUANTITATIVE DETERMINATION OF ORIGINAL PHARMACEUTICAL SUBSTANCE

Drug development & registration ◽

10.33380/2305-2066-2019-8-1-66-71 ◽

2019 ◽

Vol 8 (1) ◽

pp. 66-71

Author(s):

G. M. Alekseeva ◽

V. F. Apraksin ◽

Yu. E. Generalova

Keyword(s):

Quantitative Determination ◽

Active Compound ◽

Dissociation Constants ◽

Acid Dissociation ◽

Bromocresol Green ◽

Acid Base ◽

Indicator Method ◽

Pharmaceutical Substance ◽

Basic Properties

Introduction. The object of analysis was a newly synthesized organic substance, a derivative of 4-aminobenzoic acid and malonic ester – 4,4’-(propandiamido) sodium dibenzoate, which has an antisteatotic effect. For the quantitative determination of pharmaceutical substances, it is preferable to use titrimetric methods of analysis, since they are absolute and allow us to estimate the content of the active compound in the substance without using standard samples. Aim. The objective of this work was to develop and validate a quantitative determination method for 4.4’-(propandiamido) sodium dibenzoate. Materials and methods. The analyzed compound is a salt of a weak dibasic acid, which exhibits basic properties in an aqueous solution; therefore, for its quantitative determination, a direct acid-base titration method (acidimetry) was proposed. The method of quantitative determination of the active compound in the substance 4,4’-(propandiamido) sodium dibenzoate will be used in future studies for routine analysis, therefore a visual (indicator) method for determining the end point of the titration has been chosen. To prove the suitability of the developed method and the possibility of obtaining reliable results of the quantitative content of the active compound in the newly synthesized pharmaceutical substance the used analytical method was validated. Results and discussion. The study of the acid-base properties of the newly synthesized substance was carried out using the method of potentiometric titration, on the basis of which the values of the dissociation constants were calculated. Using spreadsheets, the pKa1 and pKa2 values were calculated using a titration model of a multi-basic acid, the pKa values of which are 7.2 and 5.0. The titration curve that was constructed from the experimental data and the curve constructed from the calculated values of the dissociation constants almost completely overlapped with each other. Based on the data obtained, a 0.1% water-alcohol solution of bromocresol green (blue) with pT=4.6 was selected for titration, the color transition interval of which falls into the titration jump of the analyte. The developed methodology was validated according to the requirements of the XIV edition State Pharmacopoeia of the Russian Federation by the following indicators: specificity, linearity, accuracy, precision (convergence and internal reproducibility), robustness, analytical domain. Conclusion. As a result of the performed studies, the values of acid dissociation constants of the newly synthesized pharmaceutical substance 4,4’-(propandiamido) sodium dibenzoate were determined, and a method for quantitative determination was developed and validated using acidbase titration.

Download Full-text