Polarography (dropping mercury electrode) – application domain Polarograph-based analysis is primarily intended for which kind of samples or systems?

Introduction / Context:Polarography is an electroanalytical technique that records current–potential curves using a dropping mercury electrode (DME) or related electrodes. It quantifies electroactive species based on diffusion-controlled waves or peaks. Understanding the sample state best suited to polarography prevents misuse and clarifies how solutions must be prepared.Given Data / Assumptions:

• Technique operates with an electrode immersed in a conductive liquid.
• Analytes must be dissolved and electroactive within the potential window.
• Supporting electrolyte ensures controlled mass transport and ohmic behaviour.

Concept / Approach:Polarography is fundamentally a solution-phase method. Samples are liquids (often miscible with aqueous or non-aqueous electrolytes) containing analytes that undergo reduction or oxidation at the electrode. Gases and solids can be analysed indirectly only after dissolution in a solvent/electrolyte; isotopic discrimination is not the native purpose of polarography (mass spectrometry excels there). Thus, among the options provided, “miscible liquids” most closely captures the appropriate medium for direct polarographic analysis.Step-by-Step Solution:

Verification / Alternative check:Analytical chemistry references place polarography under voltammetric methods for solutions; standard protocols describe preparation of liquid samples and calibration with standard additions.

Why Other Options Are Wrong:

• Gaseous mixture: Requires conversion to solution; not the direct analytical format.
• Solids: Must be dissolved or otherwise transformed for electroanalysis.
• Isotopes: Not specifically a polarographic target; mass-based techniques are preferred.

Common Pitfalls:Assuming the “mercury” in the electrode implies gas-phase mercury or solid-sample compatibility; it simply provides a renewable liquid-metal electrode surface in solution.

Final Answer:Miscible liquids