I have had difficulty creating a connection string in c# that will connect to a remote SQL server using a public IP, named instance and a port number (other than 1433). Anyo
Try this, replacing 666 with the port number you want to use, 190.190.200.100 with the IP address you want, etc.:
Data Source=190.190.200.100\MyInstance,666;Network Library=DBMSSOCN;Initial Catalog=myDataBase;User ID=myUsername;Password=myPassword;