How are Reference Standards used in the Pharmaceutical Industry?

The use of reference standards is a central component of pharmaceutical analysis and quality assurance. Reference substances (or reference standards) play a crucial role throughout the entire life cycle - from definition and manufacture right through to use in the laboratory.

What is a reference standard?

A reference standard is a highly pure, characterised substance whose identity and content are unambiguously determined. It serves as a benchmark for analytical investigations. These must be distinguished from so-called working standards, which are derived from reference standards and can be used for routine analyses. These also have assured quality, but are regularly checked against the primary standard. This distinction is essential, as primary standards are often expensive and only available in limited quantities, whilst working standards enable practical laboratory operations.

Which regulatory frameworks govern the use of reference standards?

The regulatory basis for the use of reference substances is defined in particular by pharmacopoeias such as the USP (<11>) and the European Pharmacopoeia (Ph. Eur. 5.12). Both pharmacopoeias stipulate that reference substances may only be used for their intended use and that high traceability to international standards must be ensured. They also distinguish between different types of standards, including primary, secondary and international standards, the latter of which are frequently provided by organisations such as the WHO.

Further guidelines regarding the use and handling of reference substances can be found in the EU GMP Guidelines, Part I, Chapter 6, and Part II, Chapters 5, 6 and 11, as well as in WHO Technical Report Series 885, WHO Expert Committee on Specifications for Pharmaceutical Preparations, Annex 3.

How are reference standards tested?

The use of reference substances is closely linked to their characterisation and certification. Before use, they must undergo comprehensive analytical testing. This includes methods such as NMR, HPLC, GC or Karl Fischer titration to determine identity, purity and water content. The content of a reference substance is often calculated indirectly via what is known as 'potency', by subtracting all known impurities from 100%. This systematic characterisation ensures that the substance can serve as a reliable benchmark.

Another important point is the establishment of in-house reference substances (in-house standards). As official pharmacopoeia standards are often expensive and only available in small quantities, pharmaceutical companies frequently rely on their own working standards. These are produced in-house or obtained from production batches and subsequently qualified against official standards. This requires complete documentation, validated analytical methods and proof of traceability to a primary standard.

How are reference substances used in practice?

In practice, reference substances are used for three main purposes. Firstly, they are used for quantitative determination, for example to determine the content of active pharmaceutical ingregredients or impurities. Here, the content is determined either absolutely via a mass balance or relatively via biological activity (potency). Secondly, they are used for qualitative analyses, in particular for identity testing and to verify the purity of a substance. Thirdly, they are used to verify the performance of analytical instruments and methods, i.e. to ensure that a measurement system is functioning correctly.

A key aspect of their use is correct handling in the laboratory. Reference substances must be used in accordance with the specifications of the relevant pharmacopoeia, for example regarding weighing, dilution or any drying prior to use. The information on the label - such as content, storage conditions and expiry date - must also be strictly observed. Errors in handling can directly lead to incorrect analytical results and thus jeopardise the quality of medicinal products.

Reference substances are typically used within the framework of quality control. They are used to test production batches of active pharmaceutical ingredients and finished medicinal products. This involves verifying whether identity, purity and content meet the specified requirements. Reference substances also play an important role in method development and validation, as they serve as a reference point for assessing measurement uncertainties and accuracy.

In addition to their analytical use, the management of reference substances is also of great importance. This includes aspects such as storage, stability, the necessary reanalyses and the corresponding documentation. Reference substances must be stored under defined conditions - often refrigerated or deep-frozen - to ensure their stability. Furthermore, regular reanalyses are carried out to ensure that the substance remains suitable. Typical re-analysis intervals are initially around two years and later involve annual checks.

How are reference substances documented?

A Certificate of Analysis (CoA) is issued for each reference substance, containing all relevant information. This includes the origin, date of manufacture, content, impurities and intended use of the standard. This documentation is necessary to meet GMP requirements and ensure full traceability.

In summary, reference substances are indispensable tools in the pharmaceutical industry. They enable reliable and reproducible analyses, ensure the quality of medicinal products and meet regulatory requirements. However, their use requires careful selection, comprehensive characterisation and strict adherence to handling and documentation regulations. Only in this way can it be ensured that they serve as a reliable benchmark in pharmaceutical analysis.