Embodiments of the disclosure can include systems and methods for formation fluid sampling. In one embodiment, a method can include monitoring a relationship between a first characteristic of a formation fluid extracted from a formation and a second characteristic of the formation fluid extracted from the formation, determining, based at least in part on the monitoring, that a linear trend is exhibited by the relationship between the first characteristic of the formation fluid extracted from the formation and the second characteristic of the formation fluid extracted from the formation, and determining a reservoir fluid breakthrough based at least in part on the identification of the linear trend, wherein the reservoir fluid breakthrough is indicative of virgin reservoir fluid entering a sampling tool.