Conductivity measurement is a fundamental technique used to quantify the ability of a substance to conduct electrical current. It's widely applied in various fields such as chemistry, environmental science, and engineering. Here's an overview of the basics of conductivity measurement:

1. Conductivity: Conductivity ($\kappa$) is a measure of how well a substance conducts electricity. It is the reciprocal of resistivity ($\rho$). Conductivity is usually expressed in units of Siemens per meter (S/m) or microsiemens per centimeter (μS/cm).

2. Principle of Measurement:

• Conductivity measurement is based on the principle of applying an electric field across a sample and measuring the resulting current flow. The conductivity of the sample is calculated using Ohm's Law: $\kappa =\frac{I}{V}\cdot \frac{1}{L}$, where $I$ is the current, $V$ is the voltage, and $L$ is the distance between the electrodes.
• For solutions, the conductivity depends on the concentration of ions present and their mobility in the solution. Higher ion concentration and higher ion mobility lead to higher conductivity.

3. Measurement Setup:

• Electrodes: Two electrodes are immersed in the sample solution. These electrodes are typically made of materials that do not react with the solution and have a high conductivity themselves, such as platinum or graphite.
• Cell Constant: The distance between the electrodes and their surface area determines the cell constant, which is essential for converting the measured conductance to conductivity.
• Measurement Circuit: A constant alternating current (AC) or direct current (DC) is passed through the sample using a conductivity meter. The resulting voltage drop across the electrodes is measured.

4. Calibration:

• Conductivity meters need to be calibrated using standard solutions of known conductivity. Calibration ensures accurate and reliable measurements.
• Calibration points typically include a low-conductivity standard (e.g., deionized water) and a high-conductivity standard (e.g., a standard potassium chloride solution).

5. Factors Affecting Measurement:

• Temperature: Conductivity is temperature-dependent. Most conductivity meters have built-in temperature compensation to correct for temperature variations.
• Electrode condition: Clean electrodes are essential for accurate measurements. Contamination or electrode degradation can affect measurement accuracy.
• Sample characteristics: Conductivity can be influenced by factors such as the presence of impurities, dissolved gases, and the pH of the solution.

Conductivity measurement is invaluable in various applications, including monitoring water quality, assessing the purity of solutions, and controlling industrial processes.