using System;

            using System.Text.RegularExpressions;       

public class Program

{

    public static void Main()

    {

          var inputs = new []{ "'Test string','abc'", "'Test string ','abc'", "'Test string' ,'abc'", "'Test string', 'abc'", "'Test string   '   ,   'abc'", "Test string','abc','John's test'" };

​

            foreach (var input in inputs)

            {

               var results = Regex.Split(input, @"(?<=')\s*,\s*");

               foreach (var result in results)

                  Console.WriteLine(result);

            }

    }

}