Moisture induced solid phase degradation of l-ascorbic acid Part 1: a kinetic study using tristimulus colorimetry and...

Area of Science:

• Pharmaceutical Sciences
• Physical Chemistry

Background:

• l-Ascorbic acid (Vitamin C) is susceptible to degradation.
• Solid-phase degradation kinetics and pathways are not fully elucidated.
• Moisture and air are known factors influencing ascorbic acid stability.

Purpose of the Study:

• To investigate the kinetics of l-ascorbic acid degradation in the solid phase.
• To determine the influence of moisture and air on degradation rates.
• To evaluate tristimulus colorimetry as a method for monitoring solid-phase degradation.

Main Methods:

• Solid-phase degradation studies under varying moisture conditions.
• Kinetic analysis following zero-order reaction models.
• High-performance liquid chromatography (HPLC) assay for quantification.
• Tristimulus colorimetry for color change assessment.
• Development of a method for dehydroascorbic acid determination.

Main Results:

• Solid-phase l-ascorbic acid degradation followed zero-order kinetics, influenced by moisture content.
• Exclusion of air suggested an oxidative degradation route, though dehydroascorbic acid was not detected.
• Activation energies measured by HPLC (37.57 kJ mol⁻¹) and colorimetry (33.30 kJ mol⁻¹) showed a 12.8% difference.
• Tristimulus colorimetry was more sensitive to early degradation than HPLC but lacked specificity.

Conclusions:

• Moisture significantly accelerates solid-phase l-ascorbic acid degradation following zero-order kinetics.
• Tristimulus colorimetry is a potentially rapid and non-destructive tool for monitoring l-ascorbic acid degradation onset.
• Further research is needed to identify specific degradation products and pathways.