using regular exppression can solve your problem

private void DoSplit(string str)
{
    str += str.Trim() + " ";
    string patterns = @"\w+:([\w+\s*])+[^!\w+:]";
    var r = new System.Text.RegularExpressions.Regex(patterns);
    var ms = r.Matches(str);
    foreach (System.Text.RegularExpressions.Match item in ms)
    {
        string[] s = item.Value.Split(new char[] { ':' });

//do something } }

Using a regular expression can solve your problem:

private void DoSplit(string str)
{
    str += str.Trim() + " ";
    string patterns = @"\w+:([\w+\s*])+[^!\w+:]";
    var r = new System.Text.RegularExpressions.Regex(patterns);
    var ms = r.Matches(str);
    foreach (System.Text.RegularExpressions.Match item in ms)
    {
        string[] s = item.Value.Split(new char[] { ':' });
        //Do something
    }
}