Plug unit and connection system for connecting capillaries, particularly for high-performance liquid chromatography

A connection system for connecting a capillary tube, the connection system including:

• (a) a bushing unit having a receptacle opening in which is defined a capillary tube receptacle opening, the capillary tube receptacle opening including a floor wall and a bushing capillary tube opening located in the floor wall;
• and
• (b) a plug unit including:
• (i) a plug housing having an axial borehole,
• (ii) a plug capillary tube projecting through the axial borehole of the plug housing,
• (iii) an elongated annular sealing element through which a front end region of the plug capillary tube is received so that a front end surface of the plug capillary tube is flush with a front end surface of the annular sealing element, the annular sealing element having an outer diameter that corresponds, at least in a front axial sub-region of the annular sealing element, to an inner diameter of the capillary tube receptacle opening of the bushing unit,
• (iv) wherein the plug housing is adapted to detachably connect to the bushing unit, and
• (v) a pressure piece through which a rear portion of the annular sealing element extends, the pressure piece having a front end spaced apart from a front end wall of the annular sealing element and having a rearward end surface that faces away from the front end wall of the annular sealing element, the pressure piece is in position to abut a shoulder of the annular sealing element;
• (c) wherein the pressure piece and the annular sealing element are both connected rigidly to the plug capillary tube so as to prevent relative movement between the pressure piece, the annular sealing element, and the plug capillary tube, and so that the front end region of the plug capillary tube, the annular sealing element, and the pressure piece are insertable simultaneously into the receptacle opening of the bushing unit with the front end region of the plug capillary tube projecting into the capillary tube receptacle opening in alignment with the bushing capillary tube opening;
• and
• (d) wherein when the front end region of the plug capillary tube, the annular sealing element, and the pressure piece are inserted into a fully inserted position in the receptacle opening and the plug housing is placed in the connected position, the plug housing applies an axial force to the pressure piece, the annular sealing element, and the plug capillary tube so as to press at least the front end wall of the annular sealing element against the floor wall of the capillary tube receptacle opening.