Whenever, you need to use GROUP_CONCAT with differente separator(I mean default separator is ',', But you want to change '@','#','&' etc as you want). then you have to use use SEPARATOR keyword in GROUP_CONCAT(). If you are working on laravel then you have to also use DB::raw() for write GROUP_CONCAT() inside the this function.
So, Basically how to change seprator in group_concat(), In following example i change ',' separator into '@'.you can use the following example how to use in laravel 4 and 5.
$items = DB::table('items')
,DB::raw("(GROUP_CONCAT(items_city.name SEPARATOR '@')) as `cities`"))