Application Note: Instrumental method for quantitation of colour in drug solutions
EP Colour is used to assign a colour rating to liquid samples indicative of the product quality. The original intent of using EP Colour was to improve colour communication over more ambiguous word descriptors such as ‘slightly yellow’ by visual comparison to a fixed set of 37 transparent EP liquid colour standards, all of which are yellow.
As defined in European Pharmacopoeia Method 2.2.2, the visual EP Colour Scale consists of three primary colour standard solutions (yellow, red and blue) combined with a dilute hydrochloric acid solution to make five standard colour solutions – B (brown), BY (brownish-yellow), Y (yellow), GY (greenish-yellow) and R (red) that are subsequently diluted with hydrochloric acid (10g/l HCl) to make 37 reference EP liquid colour standards – 9B, 7BY, 7Y, 7GY and 7R.
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