This probably has a simple answer, but I must not have had enough coffee to figure it out on my own:
If I had a comma delimited string such as:
string li
string s = "A,B,C";
string replaced = "'"+s.Replace(",", "','")+"'";
Thanks for the comments, I had missed the external quotes.
Of course.. if the source was an empty string, would you want the extra quotes around it or not ? And what if the input was a bunch of whitespaces... ? I mean, to give a 100% complete solution I'd probably ask for a list of unit tests but I hope my gut instinct answered your core question.
Update: A LINQ-based alternative has also been suggested (with the added benefit of using String.Format and therefore not having to worry about leading/trailing quotes):
string list = "Fred,Sam,Mike,Sarah";
string newList = string.Join(",", list.Split(',').Select(x => string.Format("'{0}'", x)).ToList());