Epimeric Separation of l-Ascorbic Acid and d-Isoascorbic Acid by Capillary Zone Electrophoresis

Abstract

Capillary zone electrophoresis (CZE) was used for separation of L-ascorbic acid (L-AA) and D-isoascorbic acid (D-IAA) in a model system. The effects of borate buffer concentration (0.05-0.25 M) and pH (pH 7.5-9.0) on migration time, resolution (Rs), and theoretical plates (N) were investigated. The migration times of L-AA and D-IAA increased with the increasing pH of carrier electrolyte (0.2 borate buffer), and the resolutions (Rs) of L-AA and D-IAA were calculated to be 12.98 at pH 9.0. Concentrations of borate buffer (pH 9.0) increased the Rs values of L-AA and D-IAA, and buffer concentrations >0.1 M were found to be effective for separation of L-AA and D-IAA. Methanol in the carrier electrolyte was also influential in improving the separation of L-AA and D-IAA, which increased with the increasing concentrations (0-10%) of methanol. The optimal separation conditions for L-AA and D-IAA were as follows: carrier electrolyte, 0.2 M borate buffer (pH 9.0); applied voltage, 25 kV, with an uncoated fused silica capillary, 75 microm (i.d.) x 57 cm.

CE methods applied to the analysis of micronutrients in foods

“…L-DHAA possesses the same vitamin activity as L-AA whereas the C 5 epimer of L-AA known as D-isoascorbic acid (D-iAA) or erythorbic acid possesses limited vitamin activity [8]. Ascorbic acid is highly sensitive to several external conditions which include light, temperature, heat, salt, pH and oxygen and enzymes [73]. As a result, precise quantification with conventional methods has been difficult [74].…”

“…In only four cases (two organic and two integrated) was L-AA not detected. Epimeric separation of L-and D-has also been carried out using CZE but in a model system by Liao et al [73]. In this study, the effects of borate buffer concentration, migration time and resolution were investigated.…”

Analysis of natural antioxidants by capillary electromigration methods

“…Several CE works have focussed on the separation and detection of ascorbic acid and other vitamins [100][101][102] while other works have been devoted to determine the amount or presence of L-ascorbic and D-isoascorbic acids [103][104][105][106] in different foods. While L-ascorbic acid is contained in most vegetables and fruits, D-isoascorbic acid does not naturally exist in foods being used as an additive due to its antioxidant activity.…”

“…This point, together with the fact that D-isoacorbic acid has only a 5 % of the L-ascorbic activity [104], has made of this separation an interesting goal in food analysis. These compounds have successfully been separated as standards by CZE using a 0.2 M borate buffer at pH 9.0 [103], from plant tissues using a similar running buffer [105], and from juices using a 50 mM tricine buffer at pH 8.8 [104], with limits of detection of 1.6 and 1.1 mg/L for L-ascorbic acid and D-isoascorbic acid, respectively [104]. A method based on MEKC using sodium deoxycholate as micellar agent was proposed by Thompson et al to replace the HLPC method used to analyze Lascorbic acid [107].…”

An Ascorbic Acid Oxidase-based Sensing Platform for Stereoselective Interaction with Ascorbic Acid and Isoascorbic Acid

“…8,9 Hence, it is urgent to develop a sensitive and rapid method for stereoselective interaction and detection of AA and IAA. Currently, various methods including high performance liquid chromatography, 10,11 capillary zone electrophoresis, [12][13][14] and electrochemical methods 15,16 have been reported for stereoselective interaction with AA and IAA. Among those methods, electrochemical sensing offers many merits, such as convenience, easy operation, low cost and high sensitivity, 17 and is gradually growing into a significant research technique for stereoselective interaction.…”