A system for separation of analytes in a liquid sample, said system comprising: • a control unit for controlling and regulating flow rate and pressure of the system; • an inlet for introducing the sample into the system; • a first column having a sorbent for trapping the analytes, said first column being switchable between a trapping mode and an elution mode, said trapping mode enabled when the inlet is in fluid communication with the first column, and said elution mode enabled when the analytes trapped in the first column are eluted;. a holding loop wherein partly separated analytes eluted from the first column and a mobile phase gradient may be stored for further separation, • two or more fluid pumps connected in parallel and controlled by the control unit to deliver a mobile phase at a flow rate of 300 nL/min to 50 μL/min through said first column at a pressure of 1 bar to 50 bar, when the column is in elution mode, • one fluid pump, or two or more fluid pumps connected in parallel, controlled by the control unit to deliver a make-up flow at a flow rate of 300 nL/min to 50 μL/min at a pressure of 1 bar to 50 bar, said make-up flow being introduced between the first column and the holding loop, wherein all said fluid pumps are controlled by the control unit to establish said mobile phase gradient, • one or more valves switchable between a low pressure position and a high pressure position, wherein said low pressure position establishes a fluid connection from the first column to the holding loop, whereas said high pressure position establishes a fluid connection with a high pressure fluid pump on one side of the loop and a conduit leading to a chromatography column on the other side of the loop, wherein the control unit is adapted to activate the high pressure fluid pump and force the gradient and analytes in said loop through the chromatography column at a flow rate of 20nL/min to 20 μL/min and a pressure of 1 bar to 3,000 bar. • a control unit for controlling and regulating flow rate and pressure of the system; • an inlet for introducing the sample into the system; • a first column having a sorbent for trapping the analytes, said first column being switchable between a trapping mode and an elution mode, said trapping mode enabled when the inlet is in fluid communication with the first column, and said elution mode enabled when the analytes trapped in the first column are eluted;. a holding loop wherein partly separated analytes eluted from the first column and a mobile phase gradient may be stored for further separation, • two or more fluid pumps connected in parallel and controlled by the control unit to deliver a mobile phase at a flow rate of 300 nL/min to 50 μL/min through said first column at a pressure of 1 bar to 50 bar, when the column is in elution mode, • one fluid pump, or two or more fluid pumps connected in parallel, controlled by the control unit to deliver a make-up flow at a flow rate of 300 nL/min to 50 μL/min at a pressure of 1 bar to 50 bar, said make-up flow being introduced between the first column and the holding loop, • two or more fluid pumps connected in parallel and controlled by the control unit to deliver a mobile phase at a flow rate of 300 nL/min to 50 μL/min through said first column at a pressure of 1 bar to 50 bar, when the column is in elution mode, • one fluid pump, or two or more fluid pumps connected in parallel, controlled by the control unit to deliver a make-up flow at a flow rate of 300 nL/min to 50 μL/min at a pressure of 1 bar to 50 bar, said make-up flow being introduced between the first column and the holding loop, wherein all said fluid pumps are controlled by the control unit to establish said mobile phase gradient, • one or more valves switchable between a low pressure position and a high pressure position, wherein said low pressure position establishes a fluid connection from the first column to the holding loop, whereas said high pressure position establishes a fluid connection with a high pressure fluid pump on one side of the loop and a conduit leading to a chromatography column on the other side of the loop, wherein the control unit is adapted to activate the high pressure fluid pump and force the gradient and analytes in said loop through the chromatography column at a flow rate of 20nL/min to 20 μL/min and a pressure of 1 bar to 3,000 bar. • one or more valves switchable between a low pressure position and a high pressure position, wherein said low pressure position establishes a fluid connection from the first column to the holding loop, whereas said high pressure position establishes a fluid connection with a high pressure fluid pump on one side of the loop and a conduit leading to a chromatography column on the other side of the loop, wherein the control unit is adapted to activate the high pressure fluid pump and force the gradient and analytes in said loop through the chromatography column at a flow rate of 20nL/min to 20 μL/min and a pressure of 1 bar to 3,000 bar.