1.First create a full back-up of the contentdatabase that you want to split!
2.Verify that you meet the following minimum requirements: If you are using Windows authentication to connect to SQL Server, the user account must also be a member the SQL Server dbcreator fixed server role on the SQL Server instance where the database will be created. If you are using SQL authentication to connect to SQL Server, the SQL authentication account that you specify when you create the content database must have dbcreator permission on the SQL Server instance where the database will be created.
3.On the Start menu, click Administrative Tools.
4.Click SharePoint 2010 Management Shell.
5.At the Windows PowerShell command prompt, type the following command:
is the name of the site collection, and is the name of the destination content database.