Project Supplier Invoice Account Generator

I amin the process of modifying Project Supplier Invoice Account Generator for one of our custom processes and need to find out the invoice_id for what it has run .

My question is : Is there a way i can link the itemkey genarated with invoice_id, how can I find out the invoice_id based on the itemkey, where is this information stored.

I need to know this very urgently, and will greatly appreciate any help on it.

Thanks