Quantitative Colour Measurement Unlocks the Potential of the European Pharmacopoeia Scale

The European Pharmacopoeia colour scale was developed to facilitate communication regarding the colour of liquid pharmaceuticals. Image Source: Pexels user bogitw

Imagine trying to describe the colour of a light yellow liquid to someone across the world. What words do you use? How do you communicate the exact qualities of this particular shade? How do you describe the degree to which it differs from another, similar but distinctly different colour? These are questions faced by multiple industries across the globe and specialized colour indexes, such as the APHA and Gardner scales, have been developed to allow us to more easily categorize hues and share colour information. Within the pharmaceutical industry, one of the most commonly used colour indexes is the European Pharmacopoeia (EP) colour scale, which was created to harmonize liquid pharmaceutical classification and facilitate communication within the industry.1 Using a range of 37 discrete colours produced via specific combinations and dilutions of three primary colour solutions, the EP scale allows industry professionals to move away from vague and imprecise descriptors to a more consistent, uniform way of identifying colour quality in APIs, excipients, and any other liquid pharmaceutical products or components.

However, determining EP scale placement has traditionally relied on visual matching of a sample to a standard within the series. This process has several major points of vulnerability:

• Colours may vary between EP standard batches due to imprecise formulation or material degradation.
• Near-clear samples are often extremely difficult to match.
• Matching requires a relatively large sample volume.
• Matching relies on subjective visual assessment, which may be negatively affected by a host of factors, including viewing environment and observer colour vision deficits.

As such, visual colour matching with EP scale standards presents major risks to accurate and consistent colour assessment and compromises the ability to make meaningful use of the scale. Quantitative colour assessment using spectrophotometric technology allows you to overcome these limits, produce accurate, repeatable colour classification, and harness the full potential of the EP colour scale.

Spectrophotometric EP colour classification allows for the assessment of even small liquid samples. Image Source: Unsplash user Nithya Ramanujam

Spectrophotometric EP Colour Classification

Spectrophotometric colour measurement easily and objectively quantifies colour information while removing unstable and subjective factors that may distort results. By analyzing the transmission spectrum of the liquid and converting that spectrum to tristimulus colour values, the spectrophotometer is able to discern colour variations so minute they are undetectable to the human eye. At HunterLab, we have correlated tristimulus colour values with the EP colour standards and integrated this index in our EasyMatch QC software, giving pharmaceutical researchers and manufacturers a simple, validated method of determining EP colour with extraordinary precision and detail. The advantages of spectrophotometric EP colour classification using HunterLab spectrophotometers and EasyMatch QC software include:

• Eliminates subjective visual assessment and human error.
• Facilitates accurate colour determination, even in small samples.
• Allows for reliable measurement of near-clear liquids that present special challenges to human visual discrimination
• Expands quality control capabilities and provides “greater insight into lot-to-lot variability and precise colour tracking of multiple lots.”2

The extraordinary level of accuracy spectrophotometric EP colour classification provides enhances both quality control of existing liquid pharmaceuticals and evaluation of new pharmaceutical formulations. As biotech researchers Karin Lucas and Kevin Maloney note, HunterLab’s EP colour measurement system is particularly useful in assessing colour behavior over time, allowing for “a more quantitative and sensitive monitoring of colour change … than traditional visual appearance testing.”3

Objective colour analysis creates a common language within the pharmaceutical industry, facilitating communication amongst stakeholders. Image Source: Pexels user Eric Bailey

Facilitating Colour Communication

The EP colour scale was originally designed as a kind of communication mechanism that would allow colour information to be easily shared within the pharmaceutical industry. Spectrophotometric EP colour classification gives you the ability to realize this goal with greater ease than ever before. Because spectrophotometers measure colour the same way every time, regardless of operator or location, you are able to produce consistent EP colour scores across your supply chain based on objective analysis, facilitating information sharing and ensuring that all stakeholders are on the same page. This is especially critical in a time of increasing globalization of research, testing, and manufacturing practices, as a common chromatic language allows actors in disparate locations to meaningfully communicate with each other regarding product formulation and behavior. The result is an expanded ability to work harmoniously to produce the highest quality pharmaceutical products.

HunterLab Quality

HunterLab has been the world leader in spectrophotometry for over 60 years and is committed to continuously expanding the possibilities of colour measurement. Our versatile range of spectrophotometric instruments and sophisticated software packages are designed to meet the unique needs of the pharmaceutical industry and enhance your colour quality control at every stage of the research, development, and manufacturing process. Contact us to learn more about our products and dedicated customer support services.