Duplicates in BindingList

Hi,

   I am facing roadblocks in creating businessrules to verify the duplicates in BindingList<>. I have an Order and OrderDetails BusinessObjects. The Order Entity has the BindingList<OrderDetails> , which is populating the Datagrid in the UI. Now i need to have a business rule that check for duplicate ProductID's in the BindingList. Could someone please let me know how to accomplish this. . Please