This is a clear-cut case for a CSV parser, so you should be using .NET's own CSV parsing capabilities or cdhowie's solution.
Purely for your information and not intended as a workable solution, here's what contortions you'd have to go through using regular expressions with Regex.Split()
:
You could use the regex (please don't!)
(?<=^(?:[^"]*"[^"]*")*[^"]*) # assert that there is an even number of quotes before...
\s*,\s* # the comma to be split on...
(?=(?:[^"]*"[^"]*")*[^"]*$) # as well as after the comma.
if your quoted strings never contain escaped quotes, and you don't mind the quotes themselves becoming part of the match.
This is horribly inefficient, a pain to read and debug, works only in .NET, and it fails on escaped quotes (at least if you're not using ""
to escape a single quote). Of course the regex could be modified to handle that as well, but then it's going to be perfectly ghastly.