The chlorine-measuring method that uses a gas-permeable membrane is the polarographic method.

The chlorine-measuring method that uses a gas-permeable membrane is the polarographic method.

• A. Polarographic method
• B. Osmotic electrode method
• C. Membrane extraction method
• D. Functionalized polysulfonic extraction method

Answer: (A)

The key idea is that a gas-permeable membrane provides a selective barrier that lets chlorine species diffuse from the water sample into the sensing area, where an electrochemical reaction occurs and generates a current. In the polarographic (amperometric) setup, the electrode responds to the diffusion-limited current produced when chlorine that has diffused through the membrane is oxidized or reduced at the electrode. Because the membrane favors chlorine diffusion and blocks other components, the resulting current is proportional to the chlorine concentration, making this method characteristic of polarographic chlorine measurement. The other methods don’t rely on gas diffusion through a membrane to drive the electrochemical signal. Osmotic electrode methods use osmotic pressure across a semi-permeable barrier to create a potential difference rather than a diffusive current from a redox reaction. Membrane extraction and functionalized polysulfonic extraction methods involve transferring chlorine into a separate phase or binding it for detection, not generating a diffusion-limited electrochemical current through a gas-permeable membrane.

The key idea is that a gas-permeable membrane provides a selective barrier that lets chlorine species diffuse from the water sample into the sensing area, where an electrochemical reaction occurs and generates a current. In the polarographic (amperometric) setup, the electrode responds to the diffusion-limited current produced when chlorine that has diffused through the membrane is oxidized or reduced at the electrode. Because the membrane favors chlorine diffusion and blocks other components, the resulting current is proportional to the chlorine concentration, making this method characteristic of polarographic chlorine measurement.

The other methods don’t rely on gas diffusion through a membrane to drive the electrochemical signal. Osmotic electrode methods use osmotic pressure across a semi-permeable barrier to create a potential difference rather than a diffusive current from a redox reaction. Membrane extraction and functionalized polysulfonic extraction methods involve transferring chlorine into a separate phase or binding it for detection, not generating a diffusion-limited electrochemical current through a gas-permeable membrane.