In the past it was necessary to use press-fit connectors with specific dimensions to connect columns of those dimensions. Modern press-fit connectors are "laser-milled" to provide highly reproducible taper angles throughout the length of the press-fit, ensuring an excellent seal. The press-fits are now treated with Agilent Ultra Inert deactivation to provide a robust and inert flow path.
Glass unions can be sealed with polyimide sealing resin which ensures a leak-free and solid connection. This method is recommended if glass press-fit unions are used: Instructions for Using Polyimide Sealing Resin with Glass Press-fit Unions