Remove space between columns

[Jose M]

I have the following code

    <div class="row" id="wrapcontenido">
        <div class="span9 columns" id="contenido">
                        Content
        </div>

        <div class="span3 columns" id="menuderecha">
                Menu
       </div>
      </div>

Displays 20 pixels of distance between the columns, but I want them
together, how I can remove that space?
any css class?

Thanks!