In the pharmaceutical industry an impurity is considered, defined the any other organic material besides the drug substance or pharmaceutical ingredients.  The impurity may be formed during the formulation or upon aging of two APIs in medicines. Stability testing is an integral part of pharmaceutical development. The primary purpose of stability testing is to provide supporting evidence on stability behavior of pharmaceutical drug products. Stability is the capacity of a drug product to remain within specifications established to ensure its identity, strength, quality and purity.