The Padres also reassigned right-handed pitcher Leonel Campos and infielder Jonathan Galvez to Minor League camp.
The Padres now have 52 players in big league camp.
Liriano, who missed all of last season after having Tommy John surgery, impressed manager Bud Black during his time in camp. He'll likely begin the season with San Antonio. Liriano hit a home run Wednesday and hit .273 over 22 at-bats this spring.
"Liriano has some tools. He's still a little rough around the edges … but he has a skill-set that plays at a higher level," Black said.
Sampson had a 7.20 ERA in three games and five innings. He'll begin the regular season with El Paso. Campos had an 11.57 ERA in five games and 4 2/3 innings. He'll likely begin the season with Class A Advanced Lake Elsinore. Galvez hit .286 in 14 at-bats and is likely ticketed for El Paso or San Antonio.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.