Conductivity Testing

Conductivity Testing is the assessment standards of a solution's ability to conduct electricity through the movement of charged ions. A common methodology is USP <644>. Conductivity is usually measured as milli-Siemens/cm (mS/cm) or micro-Siemens/cm (μS/cm)[1].

History of Conductivity Testing

Conductivity measurement can be traced back to the 19th century when scientists began to explore the electrical properties of solutions. Early experiments by researchers like Michael Faraday laid the foundation for understanding the conductivity of electrolytes[2]. The development of conductivity measurement techniques advanced significantly in the 20th century with the advent of more accurate instruments and methodologies. This progress allowed conductivity to become a widespread analytical technique used in various scientific, industrial, and environmental applications[3].

Importance of Testing Conductivity

USP <644> serves as a fundamental tool to assess the integrity and purity of solutions[1]. For instance, in pharmaceutical manufacturing, accurate conductivity readings are essential to guarantee the consistency of drug formulations. Conductivity measurement also plays a vital role in environmental monitoring, helping to assess water quality and detect contaminants. Assessing electrical conductivity in solutions has proved to be one of the most effective methods of studying ion-ion, ion-solvent, and solvent-solvent interactions as well, uncovering the answers to many questions scientists or manufacturers may have about their solutions[3]. Additionally, it is a critical parameter in research and development, aiding scientists in understanding and optimizing chemical processes, particularly those involving ionic species, or water types[4].


Image 1: Conductivity testing. Performing conductivity testing using an in-house pH and conductivity meter, to test in-progress product samples for proper specifications. This process is checked twice - before and after the filtration of a given reagent to maximize results.

Conductivity Testing for Buffers, Media, and Reagents

Buffers, reagents, and media are integral components in many scientific and industrial processes. Their specific chemical compositions, and individual conductivities can significantly influence the conductivity of solutions in which they are combined with. This occurs due to the increase in ion concentrations that reagents may introduce to the overall reaction and can lead to skewed and non-replicative results. In biotechnology and pharmaceuticals, for instance, buffers are used to maintain pH levels and stabilize reactions, and would not be able to function properly under incorrect conductivity specifications.

Conductivity Testing at Boston BioProducts

Conductivity is determined at Boston BioProducts by applying an alternating electrical current (I) across two electrodes immersed in the solution and measuring the resulting voltage (V) (see image 1 for visual). These electrodes are held together within a probe attached to a Mettler Toledo seven compact duo S213 conductivity meter, compliant with USP, EP, and JP standards. While immersed in solution, the cations migrate toward the negative electrode of the probe, and anions move toward the positive electrode, allowing current to pass through the solution. The resulting current passing through the solution is measured, determining its conductivity. This given value is then displayed to reflect the unique specifications of the tested component.

Considerations and Limitations of Conductivity Testing

Temperature of the Solution Conductivity is temperature-sensitive, with higher temperatures increasing conductance. Ensure temperature compensation for consistency.
Concentration of the Solution Extremely concentrated solutions may affect the outcome of the conductivity reading and should be diluted from a 1X to a 10X solution prior to performing the conductivity test.
Ionic Strength of Reagents Ambient Gases Ambient air can influence conductivity, particularly carbon dioxide (CO2) as it forms the carbonic acid (H2CO3), which dissociates into ions in solution.

In addition to Conductivity Testing, Boston BioProducts provides a comprehensive set of QC tests for custom reagents. Learn more about custom reagent development services.