Photochemical interaction of ascorbic acid and nicotinamide in aqueous solution: A kinetic study

Area of Science:

• Photochemistry
• Chemical Kinetics
• Analytical Chemistry

Background:

• Ascorbic acid (AH2) is susceptible to photodegradation.
• Understanding factors influencing AH2 stability is crucial for its applications.
• Nicotinamide (NA) is a common compound with potential photochemical interactions.

Purpose of the Study:

• To investigate the photodegradation kinetics of ascorbic acid (AH2) in the presence of nicotinamide (NA).
• To determine the influence of pH on the photodegradation rate and photochemical interaction.
• To quantify the concentrations of AH2 and NA in degraded solutions.

Main Methods:

• UV radiation (30 W) was used to induce photodegradation of AH2 with varying NA concentrations.
• First-order kinetics were analyzed to determine rate constants (k obs and k0).
• A two-component spectrometric method was employed for quantitative analysis of AH2 and NA.

Main Results:

• Photodegradation of AH2 was approximately twofold faster in the presence of NA compared to AH2 alone.
• Second-order rate constants (k') for the photochemical interaction increased with pH, attributed to AH2 ionization.
• The spectrometric method provided precise (±2%) and comparable results to HPLC analysis.

Conclusions:

• Nicotinamide (NA) acts as an electron acceptor, enhancing the UV-induced photodegradation of ascorbic acid (AH2).
• The rate of photodegradation is pH-dependent, increasing as ascorbic acid ionizes to ascorbyl anions.
• A validated spectrometric method is effective for determining AH2 and NA concentrations in photodegraded mixtures.