Implode, explode and spaces problem

I have a simple and complex search at one of our sites...in the simple search the user can search for all the words (AND) or any of the words (OR) using the standard one line text field common at most sites. The routines were written to check the query, make sure there are no odd characters, words less than three characters or restricted words. We explode the query on the basis of spaces, run varies checks on the keywords then implode the statement inserting the AND or OR and spaces as required. The problem is spaces. The rountine will not pick up an error with a query like: "(space)KEYWORD(space)(space)(space)KEYWORD(space)" The routine will try to contruct a query for the mysql like: "(space) AND (space) AND KEYWORD" etc etc.......obviously this query will not run properly. Any idea on how to solve the problem would be a big help: ken