A system and method are shown for performing cool, on-column sample injection into a chromatographic device having a capillary column which injection is achieved through the use of a syringe having a needle. The column diameter is minimized by the provision of an inlet assembly connected to the inlet end of the column, a sealing member disposed in the inlet assembly, for forming a fluid tight seal in the inlet end when the sample is injected onto the column to prevent the sample from escaping and for reducing the effective length of the needle at the point of insertion of the needle into the column and a guide member for reducing the effective length and for supporting the needle during insertion into the column. A temperature controller for controlling the temperature of the column in the region where the sample is injected is also disclosed. The sealing member is shown to include an elastomeric member and further the system includes a mechanism for continuously cooling the elastomeric member. The elastomeric member is shown to include a septum having a bore formed therein for passage of the needle therethrough. A new sample vial closure is also shown for use in the system, which closure applies only a minimal axial force on the needle. In such a system and method the need for a long syringe is obviated. The column inner diameter can be minimized by the system and method which permits the needle of the syringe to having a minimum outer circumference.