Yet another problem with Session with DB

[eluser]R_Nelson[/eluser]
this is how i set the DB session

Code:

function is_logged_in()
    {
        $CI =& get_instance();    
        $is_logged_in = $CI->session->userdata('is_logged_in');
        if(!isset($is_logged_in) || $is_logged_in != true)
        {                
            return false;
        }else{
            return true;
        }        
    }

it works just fine but what i'm having problems with is if i shut down firefox and come back in i have 2 sessions in the DB or if i login via IE or another computer what i would like to do is purge the older one from the database i know how to remove it but i need help with checking to see if there is more than 1 and witch one is older!