Apparatus for proportionating, injecting, and/or routing analyte sample solutions in microlitre or nanolitre scale into at least one high-pressure fluid stream, comprising: a. at least one slider plate comprising at least one central bore and two complementary bores (24, 28) in at least one row, wherein the volume of the central bore in said row determines the sample solution volume to be injected and effects the proportionating of the sample solution, b. a sample supply channel connected to said central bore in a sample loading position of the slider plate for loading an aliquot of the sample solution into said central bore, with one of said complementary bores (24, 28) in said row connecting a solvent/buffer supply inlet port with a pertinent outlet connection for sustaining the high-presssure fluid stream in the sample loading position, c. an actuator for moving the slider plate from the sample loading position into a sample injection position in which the fluid stream passes through the central bore so as to inject the sample solution volume into the fluid stream, and d. a top stator plate and a bottom stator plate sandwiching the slider plate which is supported such as to enable a linear movement of the slider plate between its loading position and the sample injection position, characterized in that said supply inlet port and said outlet connection are connected to a capillary tube by means of a fitting connection respectively, said fitting connection being provided on the top stator plate or on the bottom stator plate, wherein at least one of said fitting connections comprises an assembly comprising a compression bushing, a backing bushing and a sealing bushing being fixed by means of a buckle element (36, 39) having at least one wing such that only axial and no torsion compression forces are exerted onto the assembly, wherein: • the backing bushing has a bore for pressing the sealing bushing and the compression bushing into the backing bushing and wherein the sealing bushing and the compression bushing are each provided with a central bore (82, 84) for feeding through a capillary tube, • the bore of the backing bushing has a partly slightly conical bore end for achieving a grouting of the sealing bushing such that the inner wall- of the central bore of the sealing bushing exerts a surface pressure being effective in radial direction onto the whole of the circumference of the external wall of the capillary end within the contact area between the external wall of the capillary and the inside surface of the central bore. a. at least one slider plate comprising at least one central bore and two complementary bores (24, 28) in at least one row, wherein the volume of the central bore in said row determines the sample solution volume to be injected and effects the proportionating of the sample solution, b. a sample supply channel connected to said central bore in a sample loading position of the slider plate for loading an aliquot of the sample solution into said central bore, with one of said complementary bores (24, 28) in said row connecting a solvent/buffer supply inlet port with a pertinent outlet connection for sustaining the high-presssure fluid stream in the sample loading position, c. an actuator for moving the slider plate from the sample loading position into a sample injection position in which the fluid stream passes through the central bore so as to inject the sample solution volume into the fluid stream, and d. a top stator plate and a bottom stator plate sandwiching the slider plate which is supported such as to enable a linear movement of the slider plate between its loading position and the sample injection position, • the backing bushing has a bore for pressing the sealing bushing and the compression bushing into the backing bushing and wherein the sealing bushing and the compression bushing are each provided with a central bore (82, 84) for feeding through a capillary tube, • the bore of the backing bushing has a partly slightly conical bore end for achieving a grouting of the sealing bushing such that the inner wall- of the central bore of the sealing bushing exerts a surface pressure being effective in radial direction onto the whole of the circumference of the external wall of the capillary end within the contact area between the external wall of the capillary and the inside surface of the central bore.