using System.Collections.Generic;
public static void Main()
var list = new List<string>
"U-70754, U-70755, U-70786, U-70787, U-70788",
"U-70754, U-70755, U-70786, U-70787, U-70788",
"U-70754, U-70755, U-70786, U-70787, U-70788",
"U-70754, U-70755, U-70786, U-70787, U-70788"
var filteredList = list.SelectMany(x => x.Split(",", StringSplitOptions.RemoveEmptyEntries))
.ForEach(s => Console.WriteLine(s));