pH Testing
pH measurement is an analytical technique that quantifies the acidity or alkalinity of aqueous solutions. It provides insight into the concentration of hydrogen ions (H+) in a solution and is a crucial parameter in various scientific disciplines, especially in the fields of chemistry and biology. A common methodology for measuring this is USP <791>. The pH scale ranges from 0 to 14. Solutions with a pH below 7 are considered acidic, while those with a pH above 7 are considered alkaline or basic[1]. The pH of a solution can have a profound impact on chemical reactions, biological processes, and stability of various substances.
History of pH Measurement
The concept of pH was introduced by Søren Peder Lauritz Sørensen, a Danish chemist, in 1909. Sørensen developed the pH scale as a means of simplifying the notation of the concentration of hydrogen ions in solutions. His pioneering work laid the foundation for the modern understanding of pH and its widespread application in scientific research, industrial processes, and everyday life[2]. Understanding the importance of pH in the early 1900's has laid the groundwork in developing several types of pH-reading technologies including indicator reagents, pH test strips, metal electrode detectors, and glass electrode detectors[3], allowing for a wide variety of testing for different testing application types. Nowadays, to test biological reagents for research or manufacturing use according to USP regulations, potentiometric instruments capable of reproducing pH values to 0.02 pH units within the range of 23 to 27 degrees Celsius are often expected in maintaining product quality[1].
Importance of Testing Buffers, Reagents, and Media
Accurate pH measurement of select buffers, reagents and media play a pivotal role in scientific experimentation and quality control processes. This measurement ensures precision and reliability in scientific experiments, as deviations to known pH ranges of solutions can significantly impact solubility of reactant chemicals and reaction speeds[3]. In biological systems, maintaining the appropriate pH level is crucial for the functioning of enzymes, proteins, and cellular processes, as pH values have a direct impact of the denaturation of proteins.
pH testing is relevant to nearly all industries that deal with water. In chemical manufacturing processes, pH control of reagents allows for optimization of downstream reactions, preventing undesirable reactions and ensuring the necessary chemical transformations occur efficiently. From a reactant standpoint, any reagent with a pH higher or lower than its expected range will affect the pH of the overall system, increasing the likelihood that the expected product will either not be created, or will not match specifications.
pH Testing at Boston BioProducts
At Boston BioProducts, the pH measurement of solutions is a critical test for product quality. The process includes the following steps:
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- Calibration of the pH Meter: Before measuring the pH of a buffer solution, the pH meter is calibrated using certified NIST Traceable solutions with known pH values. This step ensures the accuracy of subsequent measurements.
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- pH measurement of sample: After calibration, the pH of the buffer solution is measured. The pH meter is rinsed with distilled water, and the probe sensor is immersed in the sample. The probe can then measure the electrical potential (voltage) produced by the tested solution, and can compare it to the potential of the known sample present internally within the glass electrode. The potential difference can then be used to determine the pH of the solution being tested.
Image 1: Correct calibration of pH meters is required to ensure accuracy of the device in testing biological reagents. While calibrating, it is important to document all derived values for future reference.
Image 2: Before and after use, the pH electrodes require rinsing using distilled water. Ensuring that electrodes are rinsed can help rid the pH reader of any debris from past use. Following the spraying of distilled water, the use of a Kimwipe is ideal to dry the affected area to prevent contamination or scratches on the probe.
Considerations and Limitations of pH testing |
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| Temperature | Temperature plays a significant role in pH measurements. With the rise in temperature, the molecular vibrations in the solution rise resulting in the ionization and formation of more hydrogen ions. The formation of more hydrogen ions eventually leads to more acidic behavior of the buffer solutions. Therefore, to achieve highest accuracy in pH determination or adjusting the pH of buffer solutions BBP diligently oversees that calibration and measuring of the pH of buffer solution is done at the same temperature. |
| Cleanliness of Electrodes | The regular and meticulous cleaning of pH electrodes holds great importance in maintaining the integrity of pH measurements. Coatings, deposits of salts, biofilms, or pollutants on the glass surface of the electrode can render them ineffective, ultimately skewing pH readings. It is imperative to clean the probe before calibration and conducting pH measurements |
| Ionic Strength of reagents | The addition of neutral salts, such as sodium chloride, can significantly impact the pH of a buffer solution by altering its ionic strength. Ionic strength, in turn, affects ionization constants, the activity of ionized species in the buffer, and the activity of hydronium ions, ultimately resulting in changes to the solution's pH. To maintain pH consistency, especially when preparing phosphate-buffered saline (PBS) or Tris-buffered saline (TBS) with varying sodium chloride concentrations, it is advisable to use combinations or mixtures of appropriate components to obtain the desired pH. |
| Dilution of reagents | Dilution of the buffer solution or addition of water (dilution) to a buffer solution can alter its pH due to reduction in ionic strength. This phenomenon is especially true in 5 X or 10 X (PBS and TBS) buffers as the pHs of the 1X diluted buffers are invariably lower than the corresponding 5x 10x buffers. In such cases the pH of the diluted buffers solutions may be adjusted with and acid or base to attain the required/desired pH. |
In addition to pH Testing, Boston BioProducts provides a comprehensive set of QC tests for custom reagents. Learn more about custom reagent development services.