Determination of Two-Steps Acid Dissociation Constants of L-Ascorbic Acid by Capillary Zone Electrophoresis

Abstract

Two-steps acid dissociation constants of L-ascorbic acid (AA) were determined through the changes in the effective electrophoretic mobility in capillary zone electrophoresis. Although ascorbic acid is oxidatively degradable in an aqueous solution, especially in alkaline conditions, the effective electrophoretic mobility of AA was successfully measured in the pH range between 1.87 and 11.97. In the analysis of the first-step acid dissociation constant (pK a1 ) at weakly acidic pH conditions, a coated capillary with 1,3-propanesultone and a pressure-assist were utilized to detect anionic AA. In the analysis of the second-step acid dissociation constant (pK a2 ) at weakly alkaline pH conditions, AA was successfully detected at the pH range up to 11.97 with the help of Cu catalyst to remove the dissolved oxygen in the separation buffer. Acid dissociation constants were independently determined as pK a1 = 4.15±0.01 and pK a2 = 12.07±0.04 by non-linear least-squares analyses. AA did not fully dissociate at the weakly alkaline pH range, and the effective electrophoretic mobility of the dianion form of AA was extrapolated for the analysis.

Development of Novel Analysis and Characterization Methods Utilizing Reaction Dynamics in a Separation Capillary

“…pK a values of acid-degradable pravastatin [18] and hexamethylenetetramine [19] were determined under degraded conditions without any interference from the degraded species. Determination of acid dissociation constants by CE was also successful with alkaline-degradable catecholamines [20], ascorbic acid [21], and flavin derivatives [22]. Heat-degradable bupropion [23] and hydrochlorothiazide [24] were also examined.…”

Noble-metal-free single-phase Co3V2O8with the structural integrity of nanofibers for the selective detection of ascorbic acid

“…2 Despite the important role of AA in a number of metabolic functions, AA is unstable in aqueous solution (aq) since it is easily oxidized to dehydroascorbic acid, which makes it difficult to quantify and detect. 3,4 Currently, several methods such as electrochemical, 5,6 electrophoretic 7,8 and spectrophotometric 9,10 techniques have been widely developed to quantify specific target biomolecules including AA. Nonenzymatic electrochemical biosensors have particularly attracted much interest due to their simple operation, fast response, and high selectivity for quantitative analysis.…”