Comparison of Chemical and Electrochemical Approaches to Abacavir Oxidative Stability Testing

At a Glance

Metadata	Details
Publication Date	2023-03-03
Journal	Sensors
Authors	Lucie Pražáková, Jan Fischer, Andrew Taylor, Anna Kubíčková
Institutions	Czech Academy of Sciences, Institute of Physics, Charles University
Citations	6
Analysis	Full AI Review Included

Executive Summary

This research compares traditional chemical oxidation (Hydrogen Peroxide, H₂O₂) against novel electrochemical methods using Platinum (Pt) and Boron-Doped Diamond (BDD) electrodes for the forced oxidative degradation of the pharmaceutical Abacavir.

Acceleration of Stress Testing: Electrochemical oxidation dramatically accelerates the required pharmaceutical stability testing. Achieving the target 15-20% API degradation took less than 10 minutes electrochemically, compared to hours or days required by H₂O₂ oxidation, even at elevated temperatures (50 °C).
Product Consistency: Both chemical and electrochemical methods produced the same two major degradation products (OP1, m/z 319.20; OP2, m/z 246.90), validating the electrochemical approach as a suitable mimic for long-term stability impurities.
Electrode Optimization: Optimal conditions were identified: Platinum achieved 15% degradation fastest at +1.15 V (7 min). BDD, operating in the radical region, achieved the fastest overall degradation rate at +4.0 V (57% loss in 10 min).
BDD Advantage: BDD electrodes demonstrated superior performance at high potentials (+4.0 V), utilizing indirect oxidation via hydroxyl radicals, which is critical for oxidizing non-electrochemically active compounds and resisting electrode passivation.
pH Dependence: Degradation kinetics were strongly pH-dependent on both electrode types, with the fastest oxidation rate achieved in ammonium acetate buffer at pH 9.0.
Predictive Power: Electrochemical oxidation produced a greater variety of degradation products (both OP1 and OP2) compared to H₂O₂ (primarily OP1), suggesting a more accurate prediction and characterization of potential impurities.

Technical Specifications

Parameter	Value	Unit	Context
Target API Degradation	15-20	%	Standard for pharmaceutical stability studies
Chemical Oxidation Time (15% loss)	>1	h	3% H₂O₂ at 50 °C
Pt Electrode Optimal Potential	+1.15	V	Achieved 15% degradation in 7 min
BDD Electrode Optimal Potential	+4.0	V	Achieved fastest degradation rate (57% loss in 10 min)
BDD Doping Ratio (B/C)	4000	ppm	Boron-Doped Diamond specification
BDD Electrode Area	0.20	cm²	Working electrode disc
Pt Mesh Electrode Area	53	cm²	Large-area working electrode
Electrolyte Concentration	0.20	mol L^-1	Ammonium acetate buffer
Fastest Degradation pH	9.0	-	Observed on both Pt and BDD electrodes
Degradation Product OP1 m/z	319.20	-	Identified by UHPLC/MS
Degradation Product OP2 m/z	246.90	-	Identified by UHPLC/MS
UHPLC Column	Kinetex C18 (100 x 2.1)	mm, µm	1.7 µm particle size
Mobile Phase Buffer	20	mmol L^-1	Ammonium Acetate (pH 7.0)
Cyclic Voltammetry Scan Rate	100	mV s^-1	Used for electrode characterization

Key Methodologies

1. Chemical Oxidation (H₂O₂ Baseline)

API Concentration: 1 mmol L^-1 Abacavir.
Oxidant: 3% (v/v) Hydrogen Peroxide solution.
Conditions: Oxidation performed at 25 °C and 50 °C.
Sampling: Samples collected for UHPLC/MS analysis at 1, 2, 3, 5, and 24 hours.

2. Electrochemical Oxidation Setup

Electrolyte: 0.20 mol L^-1 Ammonium Acetate buffer.
pH Control: Adjusted to 4.0, 7.0, and 9.0 using acetic acid and 25% ammonium hydroxide.
Reference Electrode: Ag|AgCl|3.00 mol L^-1 KCl (or Silver in 0.1 mol L^-1 AgNO₃ for Pt setup).

3. Platinum Electrode Methodology

Setup: Classic three-electrode cell (25 mL volume) with separate compartments and salt bridges.
Working Electrode: Large-area Platinum mesh (53 cm²).
Cleaning: Annealing in an upper reducing flame for 3 minutes before each measurement.
Operation: Potentiostatic oxidation, optimized at +1.15 V.

4. BDD Electrode Methodology

Setup: Low-volume (1 mL) glass batch cells without separate electrode compartments.
Working Electrode: BDD disc (0.20 cm², B/C ratio 4000 ppm).
Cleaning/Activation: Anodic cleaning using 0.50 mol L^-1 Sulfuric Acid for 10 minutes (at +2.5 V or +4.5 V).
Operation: Potentiostatic oxidation, tested up to +4.50 V (optimized at +4.0 V for fastest degradation).

5. Analytical Method (UHPLC/MS)

Instrumentation: Waters Acquity UPLC H Class with QDa mass spectrometer.
Separation: Kinetex C18 column (100 x 2.1 mm, 1.7 µm).
Mobile Phase: Acetonitrile (A) and 20 mmol L^-1 Ammonium Acetate (pH 7.0) (B).
Detection: PDA (254 nm) and Mass Spectrometry (TIC mode).

Commercial Applications

This research validates the use of advanced electrochemical materials and techniques for critical processes in the pharmaceutical and environmental sectors.

1. Pharmaceutical Development & Quality Control

Rapid Stability Testing: Implementation of electrochemical cells (using Pt or BDD) to replace time-consuming chemical stress tests, significantly reducing the time required for forced degradation studies mandated by regulatory bodies (e.g., ICH Q1A).
API Impurity Characterization: Providing a more comprehensive and accurate prediction of degradation pathways and impurity profiles compared to standard H₂O₂ methods, streamlining drug submission documentation.
High-Throughput Screening: The speed and low sample consumption of the electrochemical method enable high-throughput screening of new drug candidates for oxidative stability early in the development pipeline.

2. Advanced Electrode Manufacturing (BDD Technology)

High-Potential Electrochemical Reactors: Utilizing BDD’s wide potential window and resistance to passivation for industrial applications requiring high-efficiency radical generation (e.g., OH radicals) for oxidation processes.
Electrochemical Sensing and Analysis: BDD electrodes are ideal for sensitive voltammetric determination of organic compounds in complex biological or pharmaceutical samples due to their low background current and stability.

3. Environmental Remediation and Wastewater Treatment

Pharmaceutical Removal: The demonstrated high-efficiency oxidation of Abacavir using BDD at high potentials (+4.0 V) is directly applicable to the complete electrochemical destruction of persistent organic pollutants (POPs) and pharmaceutical residues in industrial and municipal wastewater streams.
Electrochemical Disinfection: The robust radical generation capability of BDD can be leveraged for advanced oxidation processes (AOPs) used in water purification and disinfection.

View Original Abstract

A novel electrochemical approach using two different electrode materials, platinum and boron-doped diamond (BDD), was employed to study the oxidative stability of the drug abacavir. Abacavir samples were subjected to oxidation and subsequently analysed using chromatography with mass detection. The type and amount of degradation products were evaluated, and results were compared with traditional chemical oxidation using 3% hydrogen peroxide. The effect of pH on the rate of degradation and the formation of degradation products were also investigated. In general, both approaches led to the same two degradation products, identified using mass spectrometry, and characterised by 319.20 and m/z 247.19. Similar results were obtained on a large-surface platinum electrode at a potential of +1.15 V and a BDD disc electrode at +4.0 V. Degradation of 20% of abacavir, the rate required for pharmaceutical stability studies, took only a few minutes compared to hours required for oxidation with hydrogen peroxide. Measurements further showed that electrochemical oxidation in ammonium acetate on both types of electrodes is strongly pHdependent. The fastest oxidation was achieved at pH 9. The pH also affects the composition of the products, which are formed in different proportions depending on the pH of the electrolyte.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s23052776

References

2012 - Current trends in forced degradation study for pharmaceutical product development
2016 - Forced degradation studies
2007 - Development and validation of a reverse-phase liquid chromatographic method for assay and related substances of abacavir sulfate [Crossref]
2018 - Forced degradation studies: Regulatory guidance, characterization of drugs, and their degradation products—A review
2012 - Stability testing of pharmaceutical products
2011 - How to approach a forced degradation study
2022 - Forced Degradation—A Review
2021 - Forced degradation study—A new approach for stress testing of drug substances and drug products