When and for what purpose was the Western Arms Tripplett Steel shotgun model I488 made and what is it's worth?

Triplet Steel was a mark used by Syracuse Arms and Western Arms Corp was a trade name used by Ithaca about 1928-1945. I can't remember all the history right now, but somewhere Syracuse became a part of Ithaca, so I'd say your shotgun was probably made around 1928-30. It's purpose was most likely for hunting but possibly for trap shooting.