FAQ: If I make one measurement of a nearly clear solution and select all of the EasyMatch EP indices to display the results the results are all different. How do I know which one is correct?
Answer:
Please remember that EP2.2.2 is a visual color specification not an instrumental specification. This means that if you use an instrument then you must validate your results. If you read the EP2.2.2 visual color specification you will find that there is no reference to selecting a single EP color spline. The EP2.2.2 visual color specification requires that the user compare the sample to all EP color solutions and pick the closest match. This would imply that when using the EasyMatch software that the EP 10mm 2.2.2 result is the correct answer.
We have had many pharmaceutical companies in the USA request the ability to use a single EP color spline. During their validation process (IQ/OQ/PQ) they explain why they chose the color spline. The typical use of EP color is for ageing testing. They record the color of the solution when it is made and then measure the solution at regular intervals over the course of its useful lifetime, typically 1 to 3 years. They then set a specification such as color will never be less than a certain EP color for the first year of storage.
What if the manufacturer does not know what color the sample will be after one year? Remember when it is made it is nearly colorless. What if when it was measured it was a GY7 then after one year it was a Y5. This could happen since visually GY7 and Y7 have a Chroma difference of only 0.3 and if the sample were exactly in the middle between the stock colors if could be only a Chroma of 0.15 difference from them. The typical user would say that the solution was colorless, but the instrument would pick only one index as being the closest. In this example the user might request to add a single spline index so they could stay on the same spline as the sample color changes. If the product was very clear when it is first manufactured if the user knows that as it ages it becomes Yellow, then the user can choose to use the Y scale so that the first reading is Y7 and then one year later it might be Y5 or Y4.
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