Refractometry & Polarimetry


Polarimeters - A known standard for precision in pharmaceutical quality control


Sven Boetcher, Head of Product Lines; Joerg Baempfer, Product Manager, Anton Paar OptoTec GmbH, Seelze-Letter, Germany


This article highlights the continuing importance of polarimetric analysis, with an emphasis on its critical role in the pharmaceutical industry. It explores the principles of optical activity, application areas, benefi ts of polarimetric measurement, and functionalities for error prevention. It also examines methods to achieve data integrity and compliance in a highly regulated environment. An example using amino acids demonstrates its practical applications and possible future use in the analysis of amino acids on the way to fi nal products.


Polarimetry is a long-established analytical technique, with its origins dating back to exploration of optical activity in the 19th century. Over time, it has become an indispensable device for quality control across various industries. Polarimeters, the instruments central to polarimetric analysis, provide rapid and precise measurements, making them essential for quality assurance, especially in pharmaceutical applications.


The pharmaceutical industry prescribes polarimetry for analysing active pharmaceutical ingredients (APIs), as prescribed in international pharmacopoeias like USP 781 and EUP Annex 2.2.7. These standards ensure that optical rotation measurements contribute to verifying API purity, concentration, and stereochemical properties.


Principles of optical rotation: Understanding the basics


Why is optical rotation important in pharmaceuticals?


Pharmaceuticals that are optically active have a molecule that is their mirror image. This molecule can have different pharmacological effects, toxicity, or have no effect at all. The optically active pharmaceutical and its mirror image are referred to as enantiomers. They might possess identical physical properties – however their physiological properties might differ dramatically. Enzymes have an active center which can prefer one substrate’s enantiomer over the other, as the induced fi t of different enantiomers of the same substrate differs.


Enantiomer-specifi c effects necessitate rigorous quality control to ensure the desired therapeutic outcome. Polarimetry enables precise enantiomeric analysis, making it critical for:


• New substance development: determining stereochemical properties crucial for biological activity


• Quality control: verifying API compliance with purity standards


• Purity determination: detecting minor impurities that could affect drug effi cacy and safety


Modern polarimeters, such as Anton Paar’s MCP series, are designed to meet international pharmacopoeia standards and ensure compliance with FDA 21 CFR Part 11 and GMP Volume 4 Annex 11.


High reliability with minimal effort and cost


Anton Paar’s MCP polarimeters deliver reliable, non-destructive measurements with minimal maintenance. Unlike high-performance liquid chromatography (HPLC), which requires regular upkeep, MCP polarimeters feature robust construction and advanced optics that ensure consistent performance.


Their user-friendly interfaces and automated features allow for seamless integration into laboratory workfl ows, reducing operator error and operational costs.


Advancing polarimeter technology: Measure, comply, perform


Meeting the demands of regulated industries


Working in highly regulated industries comes with certain expectations. Passing audits is a must.


Ensuring compliance and audit readiness


Qualifi cation and validation Compliance in regulated industries is often seen as a major burden since it’s considered time-consuming, and requires effort and a good understanding of key concepts. These days, manufacturers of laboratory instruments not only aim to provide excellent measuring technology, tools, services, and documentation, but also – and this is becoming more and more crucial – instrument software features that support you in your daily laboratory operations and, at the same time, help you fulfi l compliance regulations.


Instruments and systems need to operate in a fully qualifi ed environment, with validated processes and instrument-/system-specifi c qualifi cation packages, as well as qualifi ed installation support. Such packages need to follow guidelines in USP <1058> regarding analytical instrument system qualifi cation.


This initial activity and possible requalifi cation and compliant maintenance over the complete instrument lifecycle guarantee audit readiness, documented step by- step with the system qualifi cation status available at a glance.


Even small issues require time-intensive follow-up. Big ones are business-critical. Either way, that’s extra stress and costs.


Measure with the high-performing, automated MCP polarimeter series from Anton Paar. It eliminates errors before they can even occur, bringing you maximum effi ciency and reduced costs.


Accuracy up to <±0.0020° OR. Zero errors. Full compliance. Results in seconds.


Comply by complementing the capabilities of MCP polarimeters with the available high-performance data handling tools. The sophisticated software solutions provide a centralised platform for data collection, storage, and analysis, empowering pharmaceutical companies to manage vast amounts of data with ease and effi ciency. No matter if the instrument is operated standalone, or remote-controlled with the Anton Paar desktop software or in combination with the central data hub AP Connect, more than just compliance with regulatory requirements such as 21 CFR Part 11 and GMP Volume 4 Annex 11 can be taken as granted.


Perform by having perfect results in seconds for the highest effi ciency in your lab


Guided workfl ows keep training efforts low and optimise operation


The Toolmaster™ function recognises measuring cells and automatically transfers data to the instrument, which eliminates human error.


(Semi-)automated workfl ows for system suitability tests (SST) and calibration improve analysis effi ciency.


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