Ascorbic acid assisted photodegradation of methylcobalamin using corrective irrelevant absorption spectrophotometric assay: A kinetic study

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 323; p. 124902
• Main Authors: Zahid, Saima, Anwar, Zubair, Qadeer, Kiran, Ejaz, Muhammad Ahsan, Wajidi, Mehwish, Yasin, Hina, Fatima, Kaneez, Razzak, Mariam, Noreen, Aisha, Vaid, Faiyaz Hussain Madni, Ahmad, Iqbal
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 15.12.2024
• Subjects: Hydroxocobalamin; Irrelevant absorption; Methylcobalamin; Photodegradation kinetics; Spectrophotometric assay; Hydroxocobalamin; Spectrophotometric assay; Methylcobalamin; Photodegradation kinetics; Irrelevant absorption
• ISSN: 1386-1425; 1873-3557
• DOI: 10.1016/j.saa.2024.124902

Degradation scheme for the photolytic degradation of methylcobalamin (MC) in the presence of ascorbic acid (AH2). [Display omitted] •Photodegradation of methylcobalamin in the presence of ascorbic acid (AH2).•Application of linear and non-linear correction of irrelevant absorption.•First-order rate constant for the photodegradation of MC is determined.•Second-order rate constants for photochemical interaction of MC and AH2.•Fluorescence characteristic of MC in the presence of AH2 is determined. Photodegradation of drug substances leads to the formation of known and unknown degradation products. These unknown degradation products interfere and give erroneous results because of absorption on analytical wavelengths. This interference could be eliminated using the correction of irrelevant absorbancies. This study is based on the application of linear and non–linear correction of irrelevant absorption for the determination of methylcobalamin (MC) and hydroxocobalamin in the photolytic degradation assisted by ascorbic acid (AH2). MC follows first–order degradation kinetics and the rate of degradation (kobs) ranges from 1.99–2.34 × 10−2, min−1 at pH 2.0–12.0. The second–order rate constants (k2) for the photochemical interaction of MC and AH2 are in the range of 17.9–60.3 × 10−2 M−1, min−1 (acidic region) and 10.3–24.6 × 10−2 M−1, min−1 (alkaline region). The k2–pH profile was found to be bell–shaped and the maximum rate of degradation in the presence of AH2 is at pH 5.0 (60.3 × 10−2 M−1, min−1) due to the protonation of MC. However, in alkaline pH, the rate of photodegradation decreases due to the ionization form of AH2 which is AH− species.