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Factors Influencing Microbial Growth: pH01:29

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Microorganisms are classified as acidophiles, neutrophiles, or alkaliphiles based on their pH growth preferences, reflecting their adaptations to specific environments. Maintaining a stable intracellular pH is critical for macromolecular stability and enzymatic activity, which can be challenged by external pH variations.Neutrophiles, such as Escherichia coli, grow optimally between pH 5.5 and 8.0. These microorganisms inhabit neutral or slightly acidic environments and employ mechanisms like...
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Hydronium and hydroxide ions are present both in pure water and in all aqueous solutions, and their concentrations are inversely proportional as determined by the ion product of water (Kw). The concentrations of these ions in a solution are often critical determinants of the solution’s properties and the chemical behaviors of its other solutes. Two different solutions can differ in their hydronium or hydroxide ion concentrations by a million, billion, or even trillion times. A common means of...
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For an ideal solution, the pH is defined as the negative logarithm of the hydrogen ion concentration. For a non-ideal solution, an accurate measurement of the pH must consider the negative logarithm of the hydrogen ion activity rather than concentration. In such a solution, the pH can be more accurately defined as the negative logarithm of a product of the hydrogen ion concentration and its activity coefficient.
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Critical Aspects of pH Measurement for Bacteriostatic Water for Injection.

Jinbo Hu1, Ali Kyad1, Kathleen Burke1

  • 1Attribute Sciences, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA, 91320, United States.

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|March 4, 2023
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Summary

Accurate pH measurement of bacteriostatic water for injection (bWFI) is challenging due to its low ionic strength. This study characterizes critical factors like probe suitability and meter settings to ensure reliable bWFI pH results.

Keywords:
Bacteriostatic water for injectionHigh purity waterpH

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Area of Science:

  • Analytical Chemistry
  • Pharmaceutical Science

Background:

  • Bacteriostatic water for injection (bWFI) is a common parenteral pharmaceutical diluent.
  • bWFI lacks buffering capacity and has low ionic strength, complicating accurate pH measurement.
  • Current United States Pharmacopeia (USP) guidelines for bWFI pH measurement do not fully address these analytical challenges.

Purpose of the Study:

  • To characterize the critical factors influencing accurate pH measurement of bWFI.
  • To raise awareness of the challenges in measuring the pH of low ionic strength pharmaceutical solutions.
  • To provide recommendations for reliable routine bWFI pH measurements.

Main Methods:

  • Comprehensive characterization of the bWFI pH measurement process.
  • Evaluation of probe suitability, measurement stabilization time, and pH meter settings.
  • Assessment of the impact of adding KCl on ionic strength and measurement consistency.

Main Results:

  • bWFI pH measurements are prone to long response times and noisy signals, leading to inconsistent results.
  • Factors like probe selection and meter settings significantly impact bWFI pH measurement accuracy.
  • Even with USP-recommended KCl addition, variability persists without careful control of measurement parameters.

Conclusions:

  • Standard pH measurement protocols may be inadequate for bWFI due to its unique properties.
  • Careful consideration of probe suitability, stabilization time, and meter settings is crucial for reliable bWFI pH determination.
  • The findings and recommendations are applicable to pH measurements of other low ionic strength pharmaceutical solutions and water samples.