Unable to write to config file

[eluser]Dsyfa[/eluser]
Hi,

I have some fields in my config that I would like to modify dynamically.

Code:

/*
|--------------------------------------------------------------------------
| Global Meta Data
|--------------------------------------------------------------------------
*/
$config['md_keywords'] = 'lorem, ipsum';
$config['md_description'] = 'Lorem - Ipsum.';

This is the code that I'm using to modify the above fields.

Code:

$data[ 'keywords' ] = $this->input->post( 'keywords', true );
$this->config->set_item( 'md_keywords', $data[ 'keywords' ] );

Where am I going wrong?

Thanks