The assay of sulpha drugs by polarography is a method used to determine the concentration of sulphonamide compounds, which are commonly used as antibacterial agents. Polarography is an electrochemical technique based on the reduction or oxidation of a compound at an electrode (typically a dropping mercury electrode) while measuring the resulting current as a function of applied potential.


Here’s an outline of the process:

1. Basic Principle:

Polarography measures the current that flows in an electrochemical cell as a function of a gradually changing potential applied to a working electrode (usually a mercury electrode). The analyte (sulpha drug) undergoes a reduction or oxidation reaction at a specific potential, which causes a peak or wave in the current response.

2. Steps Involved:

  • Preparation of Solution: A known concentration of the sulpha drug is dissolved in a suitable solvent, usually containing an electrolyte like potassium chloride to maintain conductivity in the solution.

  • Polarographic Setup: The solution is placed in a polarographic cell that contains a reference electrode, working electrode (dropping mercury electrode), and a counter electrode. The potential is applied between the working and reference electrodes.

  • Reduction of Sulpha Drug: Sulpha drugs are reduced at specific potentials. For example, the nitrogen-containing groups in sulphonamides can be reduced to amines, producing a measurable current.

  • Recording Polarogram: As the potential is scanned, the current response is recorded. The current increases when the drug undergoes a reduction at a characteristic potential, forming a wave on the polarogram.

  • Quantification: The height or area of the wave is proportional to the concentration of the sulpha drug in the solution. By comparing this to a standard curve made with known concentrations, the unknown concentration can be calculated.

3. Advantages:

  • Sensitivity: Polarography is highly sensitive to small concentrations of sulpha drugs.
  • Selectivity: Different sulpha drugs have characteristic potentials, allowing for the selective determination of specific drugs.

4. Application:

This method is often used for quality control in pharmaceutical formulations, ensuring that sulpha drugs are present at the correct concentration.

By measuring the reduction wave, the concentration of sulpha drugs in a sample can be determined precisely.