September 28, 2023

Chemical vs. Physical Stability of Formulations

physical stability of formulations

Physical and chemical stability play a crucial role in the development, manufacture, and storage of a wide range of different product types, including pharmaceuticals, cosmetics, foods, and agrochemicals. However, there are some important distinctions in the origins of physical and chemical stability and also in the experimental techniques used to measure them.

Physical Stability

Physical stability refers to the ability of a formulation to maintain its physical properties, such as appearance, texture, and particle size, over time. A great deal of effort and research has been put into preparation methods to improve the physical stability of formulations, as poor physical instability can lead to issues such as sedimentation, creaming, and caking.1 Physical instability can also have effects on the efficacy and even safety of the product.2

The overall physical stability of a product can be affected by various factors, including temperature, humidity, and light exposure. For example, during storage, shipping, or usage, exposure to high temperatures can lead to phase separation or variations in particle size, potentially affecting customer perception and satisfaction.3

formula stability comparison

Chemical Stability

Chemical stability, on the other hand, refers to the ability of a formulation to maintain its chemical integrity and potency over time. Integrity and potency really refer to the molecular structures of the active ingredients in a product and whether they remain intact and unchanged. Chemical instability can lead to degradation of the drugs or chemicals, which can affect its efficacy, safety, and shelf life and is normally influenced by pH fluctuations, oxidation, hydrolysis processes, or bacterial activity.

Oxygen is highly problematic when it comes to chemical stability, as many drug molecules will react with oxygen, undergoing an unwanted chemical change. Reactions with oxygen lead to degradation and the formation of impurities and degradation products. Hydrolysis, which can occur on exposure to water, is a similar process that results in similar problems with the formation of new, unwanted compounds.

chemical stability

Measuring Stability

The phenomena contributing to chemical and physical stability in a sample differ; therefore, they require distinct measurement techniques for analysis.

Physical stability is usually assessed by visual inspection and long-term testing – it can take up to several months to assess whether a sample has any instabilities. Sedimentation and creaming tests are crucial in emulsions to assess whether particles remain suspended, settle to the bottom, or separate from the solution.4

Understanding particle size is crucial for determining and predicting physical stability and performing rheological measurements to understand the physical and mechanical properties of the final product. Conducting a comprehensive physical and long-term stability assessment can be a rather time-consuming process. Advanced analytical instrumentation can enhance testing throughput, provide greater objectivity, and allow for analysis of the product in its native state.

Chemical stability is usually assessed with analytical methods that are used for chemical identification, such as liquid or gas chromatography (HPLC – GC), mass spectrometry (MS), and infrared spectroscopy (FTIR). These methods help identify and quantify any degradation products or impurities that may form due to chemical instability. In addition, stability studies are conducted under various conditions such as temperature, humidity, and light exposure to determine the shelf life of the drug product.

measuring chemical stability

Turbiscan Technology

When it comes to physical testing, Formulaction has the most extensive range of top-of-the-line analyzers to help you perform comprehensive and informative testing to improve your product ranges.

The Turbiscan instrumentation series has devices for aging, shelf-life, dispersibility, redispersion, phase separation, destabilization and aggregation tests, covering the full profile of potential physical instabilities in your product. For certain products, such as crude oils and fuels, that require specialist handling, Formulaction provides dedicated instrumentation to address many of these challenges and streamline your testing process.

Formulaction recognizes the many challenges of working in the modern laboratory, such as the importance of small-footprint instruments and rapid data analysis to accompany measurements. Thus, all of Formulaction’s devices have been designed with speed and efficiency in mind, aiming to minimize the lab footprint. They come equipped with one-click stability evaluations.

Engineered for user-friendliness, the Turbiscan range requires no expert operators and offers testing conditions between 20 to 60 °C, ensuring your products’ stability in any environment upon market release. The inclusion of quantitative analysis simplifies product comparisons and allows you to gauge the effectiveness of process improvements and design changes.

Several instruments, including the Turbiscan Tower and Trilab, are capable of performing various types of measurements and tests, with the Turbiscan Lab being recognized as the global standard for stability analysis.

Shelf-Life Prediction Turbiscan

To find out how you can outperform the competition by accelerating your stability studies with more accurate, quantitative data, contact us today. Our team of experts will outline why the Turbiscan could be the ideal solution for your physical stability testing needs.

References and Further Reading

  1. Gardner CR, Walsh CT, Almarsson Ö. Drugs as materials: Valuing physical form in drug discovery. Nat Rev Drug Discov. 2004;3(11):926-934. doi:10.1038/nrd1550
  2. Gao, Y., Gesenberg, C., & Zheng, W. (2017). Oral formulations for preclinical studies: principle, design, and development considerations. In Developing solid oral dosage forms (pp. 455-495). Academic Press.
  3. Müller RH, Radtke M, Wissing SA. Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) in cosmetic and dermatological preparations. Adv Drug Deliv Rev. 2002;54:131-155. doi:10.1016/S0169-409X(02)00118-7
  4. Pal R. Modeling of sedimentation and creaming in suspensions and pickering emulsions. Fluids. 2019;4(4). doi:10.3390/fluids4040186

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