The kit contains a set of seven brownish yellow color reference standards (identified sequentially from BY1 to BY7) and 3 empty sample cells. The solutions are produced from 3 primary metal salt solutions of ferric(III) chloride, cobalt(II) chloride, and copper(II) sulfate, in accordance with chapter 2.2.2 ′Degree of colouration of liquids′ of the European Pharmacopoeia (Ph. Eur.).