split content database and attach to multiple site collections

Hi,

I have a site collection with five sub sites for departments and content database size is reached to 200 GB. We are using this sites for document management. Now i want to create a new site collection for each department and attach department related data by splitting existing content database.(as per microsoft one site collection can have one Content Database)

How can i achieve this scenario? Please provide me a steps for this. 

Any help would be greatly appreciated.

Thanks...