string[] arrCols = format.Split(":");
char[] cr="[]:".ToCharArray();
string[] Format = "[Col1] : [Col2] : [Col3] : [ColX]".Split(cr);
foreach(string s in Format)
{
Console.WriteLine(s);
}
string[] columns = System.Text.RegularExpressions.Regex.Split("[Col1] : [Col2] : [Col3] : [ColX]", " : ")
foreach (string column in columns) {
// do whatever with column
}