<?php
$str = 'this is a string  "that has quoted text" "" inside.';
var_dump ( preg_split('#\s+("[^"]*")\s+|\s+#', $str, -1 , PREG_SPLIT_DELIM_CAPTURE) );
?>

array(7) {
  [0]=>
  string(4) "this"
  [1]=>
  string(2) "is"
  [2]=>
  string(1) "a"
  [3]=>
  string(6) "string"
  [4]=>
  string(22) ""that has quoted text""
  [5]=>
  string(2) """"
  [6]=>
  string(7) "inside."
}