WP Query exclude category_name

I’ve got two loops.

One loop pulls the last four items from a category called “featured” thus:

$my_query = new WP_Query(‘category_name=featured&showposts=4’);

I’d like to have a second loop which pulls the last 8 items for every category EXCEPT featured. I wrote it using the minus sign to remove the unwanted category as:

$my_query = new WP_Query(‘category_name=-featured&showposts=8’);

But that does’t work. Any ideas of a better way of doing this?