An unknown peak detected in a stressed sample is identified using UV absorption and tandem HPLC-Mass Spectral analysis and finally confirmed with the authentic sample. Its identity is confirmed as 2,4-diethyl-9H-thioxanthen-9-one, a photoinitiator which is directly linked to the UV cured ink on the foil used in market packaging. Levels are quantitated and shown to be significantly below industry standards for formal safety qualification thus alleviating concern for patient safety. Detailed analysis of the product packaging scheme indicates the mode of contamination arises from the UV cured ink printed foil configuration in production.