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Image of medication for article on drug stability testing.
Published On: August 31st, 2021
Stability testing of pharmaceutical products such as medications in pills, creams, liquids, etc., is a critical characteristic of any pharmaceutical agent. Stability not only indicates how long medication is effective when sitting on a shelf but patient safety can also be threatened when some medications break down over time or when exposed to light or heat.As the United States Pharmacopeia explains, “Stability is the extent to which a product retains, within specified limits and throughout its period of storage and use, the same properties and characteristics that it possessed at the time of its manufacture.” It is clear how the stability testing of pharmaceutical products is the backbone of the pharmaceutical industry.

How Are Pharmaceutical Products Tested for Stability?

Directly measuring the potency of pharmaceutical over a time period and when exposed to different conditions is the gold standard for determining stability. However, this method is time-consuming and costly. Consequently, it is rarely performed. Instead, measures such a pH give an excellent clue that changes are occurring. Therefore, pH changes are often used for the stability testing of pharmaceutical products.

Briefly, pH measures the acidity of a solution. All pharmaceutical agents have a standard pH, and a change in the pH is an excellent indicator that the agent is undergoing changes that will alter its safety and potency. Hence, stability testing for pharmaceutical products often uses pH as an easy, accurate measure of stability.

Additionally, the stability testing of pharmaceutical products involves more than just testing the active ingredient. Medications have other inert ingredients such as buffers and binders to hold the compound together or prevent the active ingredient from precipitating out of a liquid (e.g., in a syrup). Measuring the pH of buffers and binders can be equally important when stability testing of pharmaceutical products.

What Is A pH Meter Used For?

A pH meter is used to measure the degree of acidity or alkalinity of a solution. It was developed in 1909 by a Danish Chemist named Søren Sørensen. By calculating the concentration of free hydrogen ions in a solution (H+) and plotting this concentration on a logarithmic scale, Sørensen devised an easy to understand the measure of 0 – 14 where 0 is the maximum acidity of a solution with the most hydrogen ions, and 14 is the maximum alkalinity with the least hydrogen ions. Since that time, stability testing of pharmaceutical products has used these meters and Sørensen’s pH scale.

When performing stability testing of pharmaceutical products, a pH meter using two electrical probes submerged in the solution acts as a battery. The amount of voltage that passes from one electrode to the other indicates how many free hydrogen ions are present, hence the solution’s pH.

With the rapid speed at which pharmaceutical companies try to develop new drugs to put into the marketplace, rapid pH testing of pharmaceutical products becomes vital. Competition among various companies can be intense as many companies work to develop similar drugs simultaneously.

Why pH Meter Calibration Is Important

As it is vital to perform stability testing of pharmaceutical products by measuring the pH over time and following exposure to various light and temperature conditions, it makes sense that calibrating the pH meter is extremely important. Cleaning, calibrating, and maintaining a pH takes a constant and consistent effort by a laboratory technician.

pH meters are delicate pieces of equipment designed to measure a solution’s acidity precisely, accurately, and reproducibly. Therefore, they need to be in perfect condition if used for stability testing of pharmaceutical products.

There is significant training required for a technician to know how to clean and maintain the electrodes of a pH meter properly. Calibration is also crucial to ensure accurate readings. Stability testing of pharmaceutical products quickly becomes meaningless if a pH meter is not maintained (including cleaned after every single use and calibrated as recommended by the manufacturer). As an example, one manufacturer gives the following recommendations for cleaning their manual pH meter:

  1. Soak the electrode in a cleaning solution or a specific solution depending on the solution just tested for at least 15 minutes. This will allow any microscopic contamination or solid particles to dissolve from the electrode.
  2. It is best to use a cleaning solution that is created based on the solution just tested. So different substances with different levels of acidity should each have their cleaning solution to ensure the electrodes are completely free of any residual tested sample.
  3. Rinse the electrode using deionized water and soak the electrode in a pH neutral storage solution for a minimum of 2 – 3 hours although soaking overnight is best.
  4. Run the calibration protocol.

pH Meter Automation<

With the above example of just a part of the manual work done by a technician, pH meter automation has become an ideal option for any laboratory performing stability testing of pharmaceutical products. The time saved is tremendous as the technician who would have been spending hours properly maintaining the pH meter is now free to do other tasks. Also, there is no exposure by personnel to the reagents used in the cleaning and testing process, so the safety of individuals is much greater.

As mentioned earlier, that competitive edge needed when competing among pharmaceutical manufacturers can be achieved with rapid pH testing of pharmaceutical products by automated pH meters.

Measuring the pH of viscous liquids can be especially challenging as the readings are rarely consistent with traditional pH meters. The options include purchasing a pH meter for viscous samples or simply changing a probe on an automated pH meter. Obviously, the easier, less expensive, and more versatile solution is to automate pH readings. In this way, rapid pH testing of pharmaceutical products will be dramatically quicker, easier, and more reliable.

Hudson Robotics pH Meter Automation

Hudson Robotics has been the leader in life science and pharmaceutical laboratory automation for nearly 40 years. To learn more about stability testing of pharmaceutical products and all aspects of laboratory automation to ensure you maintain that competitive edge, contact Hudson Robotics today.