Why don't you have a control for First Name and another control for Last Name since you are splitting the name anyway??? You can always concatenate the first and last to get the full name.
Then you can check for first and last - if either control is empty/null, then set the focus to the control that has missing data with an error message to fill in the control.
BTW, how do you handle names like "Jose De La Cruz", "Emilo De Leon Arroyo" or "Annie Lynn Wilson"???