Stability-Indicating Related Substances HPLC Method for Droxidopa and Characterization of Related Substances Using LC-MS and NMR

Ultrasound Assisted Electrochemical Deposition of Polypyrrole - Carbon Nanotube Composite Film: Preparation, Characterization and Application to the Determination of Droxidopa

Background:

Nowadays, polymeric composites modified with carbonaceous nanomaterials have been popular due to their greater application potentials in many application fields. However, the structural consistency of the composite prepared by electropolymerization suffers from agglomeration of Carbon Nanotubes (CNTs) probably due to their poor dispersion in the coating solution. Present study describes a new synthesis route for the preparation of polypyrrole/CNT composite film on a Glassy Carbon Electrode (GCE) via combining the ultrasonication and electrochemical pulsed deposition for the first time. The performance of the composite film was tested by monitoring the electrochemical oxidation of droxidopa which is used as a new psychoactive drug and synthetic amino acid precursor which acts as a prodrug to the neurotransmitters.

Methods:

The polypyrrole/CNT composite film was deposited onto a glassy carbon electrode via combining the ultrasonication and electrochemical pulsed deposition. The composite film was characterized by Scanning Electron Microscopy (SEM), Fourier Transfer Infrared Spectroscopy (FTIR), Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV). Then after, the electrochemical behavior of droxidopa was investigated on the GCE/PPy-CNT electrode.

Results:

SEM images of the surface morphology have revealed a more ordered film formation and enhanced conductivity of the surface has been confirmed by EIS measurements. The synergetic effect of this composite film was tested by monitoring the electrochemical oxidation of a new psychoactive drug; droxidopa at 0.45 V. The influence of solution parameters such as medium pH, pyrrole concentration and amount of CNT along with the instrumental parameters including applied pulse number on the peak formation was investigated by aid of cyclic voltammetry. Under the optimal conditions, by monitoring the oxidation peak in dp mode, two linear ranges have been observed in 4 - 20 μM which is well suited for droxidopa analysis in pharmaceutical preparations. The limit of detection (S/N=3) was calculated as 1.3 μM.

Conclusion:

Present study offers a fast, easy and sensitive method for the determination of droxidopa by providing a novel route for the preparation of PPy-CNT composite films for any further studies.