[Spectrophotometric determination of codeine through charge-transfer reaction]

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Codeine is an important pharmaceutical agent.
• Accurate quantification of codeine is crucial for quality control.
• Charge-transfer reactions offer potential for developing new analytical methods.

Purpose of the Study:

• To investigate the charge-transfer reaction between 7,7,8,8-tetracyano-quinodimethane (TCNQ) and codeine.
• To develop a spectrophotometric method for the determination of codeine.
• To explore the mechanism and thermodynamic parameters of the charge-transfer complex formation.

Main Methods:

• Spectrophotometric analysis of the reaction between TCNQ and codeine in acetone.
• Optimization of reaction conditions for codeine determination.
• Validation of the developed method using Beer's law and recovery studies.

Main Results:

• Stable charge-transfer complexes were formed, exhibiting a bathochromic shift up to 843 nm.
• A linear relationship (Beer's law) was observed for codeine concentrations between 0.1-1.6 µg/mL.
• The apparent molar absorptivity was 1.7 x 10^4 L·mol⁻¹·cm⁻¹, with high recovery rates (98.94–99.12%) in pharmaceutical samples.

Conclusions:

• A simple, rapid, accurate, and selective spectrophotometric method for codeine determination was successfully developed.
• The method is suitable for the quantification of codeine in pharmaceutical preparations.
• The study provides insights into the charge-transfer complexation mechanism and thermodynamics.