Principle of polarography – which sample state is analyzed? Polarography (dropping-mercury-electrode voltammetry) is primarily used to analyze which type of samples?

Introduction / Context:
Polarography is an electroanalytical technique employing a dropping mercury electrode (or its variants) to record current–voltage curves and quantify electroactive species. Knowing the physical state and preparation of samples suited to polarography helps avoid conceptual errors about where the method applies.

Given Data / Assumptions:

• Technique: polarography/voltammetry at liquid interfaces.
• Working electrode immersed in an electrolyte solution.
• Analytes must be soluble and electroactive within the potential window.

Concept / Approach:
Polarography fundamentally operates in the liquid phase—aqueous or non-aqueous solutions—where ions or molecules undergo reduction/oxidation at the electrode surface. While gases and solids can be studied indirectly (after dissolution or via other techniques), the direct application is to liquid solutions. The “isotonic solutions” option is a specific subset of liquids and not the general answer expected in a fundamentals question.

Step-by-Step Solution:

Verification / Alternative check:
Analytical chemistry texts position polarography under solution electrochemistry with calibration curves for dissolved ions and organics.

Why Other Options Are Wrong:

• Isotonic solutions: Too narrow; polarography applies to many liquid solutions, not only isotonic ones.
• Gases / Solids: Not directly analyzed without dissolution or different instrumentation.

Common Pitfalls:
Assuming the mercury drop implies mercury vapor/gas analysis; the electrode simply provides a renewable liquid metal surface in a solution.

Final Answer:
Liquids