$recent->query of cat problem

The following is a portion of code from my function.php:

$recent = new WP_Query();
$catID = "3";
$recent->query("cat=$catID");

$catID = “3” works.
$catID = “4” works.
$catID = “23” does NOT work.

In order to get a double digit variable to work, I have to change the double quotes in $recent->query to single quotes. But, with single quotes, the single digit variable will not work.

The problem comes when I loop this function and some variables are single digits, some double.

Thank you for any help you may be able to offer.