Using precision colour stability to achieve brand trust

A client wanted to ensure colour consistency in pharmaceutical capsules, following regulatory required modifications to the capsule formulation. 

 

Any variation in capsule and tablet colour could raise concerns among healthcare professionals and patients, as colour shifts may indicate broader changes in the product. Therefore, it was critical to assess and maintain consistent colour stability across batches, ensuring that any potential changes remained within acceptable limits to uphold product integrity and trust.

 

To evaluate potential colour discrepancies, a series of comprehensive tests can be conducted. These tests ensure that any variations in colour are detected and assessed, whether they occur during production or as a result of exposure to external conditions once the product leaves the factory.

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Colour measurement

 

Colour measurement can be carried out using a variety of different techniques and equipment, allowing for objective measurement under specific lighting conditions. For this client’s product, RSSL used the DigiEye System (700mm Cube) which enables sample views from directly above and calibrated colour images.

Figure 1 - DigiEye scanner with bespoke capsule holder

 

To simulate typical daylight conditions when viewing the product, the CIE standard illuminant D65 was used, approximating a colour temperature of 6500 K. Utilising our 3D printing expertise, we designed and manufactured a custom holder tailored specifically for the analysis.

 

By combining the system’s software with the bespoke 3D-printed holder, RSSL was able to simultaneously analyse all 25 samples, isolating the colour values of each individual capsule.


This approach also allowed for detailed filtering of the image to identify components with varying colours or degrees of separation, enabling an in-depth assessment of colour variance across the entire sample set as well as each capsule. 

With a large number of samples, the ability to rapidly image the set and assess colour differences between individual capsules and the average value is not only highly beneficial but also crucial. The total colour difference (ΔE) for each capsule, compared to the average, was automatically calculated using the ΔE2000 colour difference method.

 

Figure 2: Delta E 2000 Calculation

The colour data was calculated for each capsule separately whilst still providing high-quality images of all of the samples under the same illuminations and conditions. This analysis can also be carried out on capsules with multi colours, as demonstrated in Figure 3 using a capsule with a yellow and red portion. 

 

The results determined that the variation in colour between each capsule was very low. The majority of these results would not be perceptible to the human eye (<1 ∆E), with the remaining results within the region only perceptible through training/close observation (1 - 2 ∆E).

 

Using this technology not only demonstrates the very subtle colour differences in samples which are non-perceptible by the human eye, but also the ability to obtain this information quickly and accurately. 

Figure 3 - Box plot of capsule colour variation

Capsule stability testing

 

To determine the photostability of a clients product, the capsules were placed into a photo stability cabinet for direct exposure for approximately two weeks. The same sample set encased in foil was also added to the test as a reference. Both sets of capsules were exposed to light with a total lux exposure of 2.7 MLuxh and a UV-A exposure of 832 Wh/m2.

Figure 4: Pink capsules - control reference

Figure 5: Pink capsules - exposed

The colour measurements were taken of both the exposed capsules and the reference capsules from the pink capsule samples. The average colour difference seen was a ∆E value of 6. 77 of the exposed capsules compared to the reference capsules.

 

 

The results determined a clear perceptible colour difference in the samples after long term light exposure despite the samples looking very similar at a glance was identified (Figure 6). RSSL’s capabilities can also include exposure to a variety of environmental conditions available, which in this case, the client didn’t require.

 

Figure 6: Post exposure colour difference swatch (Left - control, Right - exposed)

 

 

Summary

 

The DigiEye system is an effective technology for precise colour measurement of pharmaceutical capsules and tablets. It captures high-resolution images under controlled lighting conditions, such as the CIE standard illuminant D65, to simulate daylight. The system also allows for simultaneous analysis of multiple samples, isolating and measuring the colour values of individual capsules or tablets.

 

Not only on a multiple level, but also enables detailed examination of colour consistency within each sample and across different sections, helping to identify any variations or anomalies in colour that could indicate broader issues with the formulation or production process.

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