If you want to break "John Smith" into "John", "Smith" and "J ane Doe" into "J ane", "Doe" then split is not for you - it will always split on each space, for "J ane Doe" will become "J", "ane", "Doe".
Substring can do it:
string input = "J ane Doe";
int lastSpace = input.LastIndexOf(' ');
string firstName = input.SubString(0, lastSpace);
string lastName = input.Substring(lastSpace);
Or you could use a Regex:
(?<firstName>.*)\s(?<lastName>[A-Z][a-zA-Z-]*)$
Which would capture the last name by looking for the final capitalized word.