Abstract: An inlet seal assembly for sealing an injection port member in a chromatography instrument, comprising an injection port member having a bottom surface with a raised metal ring, an inlet seal member with an upper surface, a peripheral groove formed in the upper surface of the inlet seal member, a soft ring made of resinous plastic material positioned in the peripheral groove of the inlet seal member opposite the raised metal sealing ring of the injection port member, a reducing nut holding the inlet seal member against the injection port member, and threads connecting the reducing nut to the injection port member whereby to press the soft ring of the inlet seal member against the raised metal sealing ring of the injection port member to form a seal between the sealing ring and the injection port member. A method of making and using the inlet seal assembly.