The sudden appearance of an unknown peak during an HPLC analysis of a pharmaceutical product can be a critical finding causing delays and requiring considerable resource (both time and money) to resolve. The immediate need to investigate an unknown peak is a common problem and is generally accompanied with aggressive timelines and stressful conditions and the issue can be caused by many things which can range from simple sample preparation contamination, all the way to unexpected degradation/stability properties of the product. In any case, it is essential that a rapid and effective investigation take place to quickly determine the identity of the anomalous peak and determine the root cause of its presence in the product.