Patent ID: 7722764

Claim:
A gradient pump apparatus comprising: a gradient pump capable of mixing and feeding plural types of solutions; an isocratic pump capable of feeding a solution; a switching valve for switching the solutions fed from said gradient pump to be sent to and analytic section with the solution fed from said isocratic pump, or to be drained; a first pressure sensor for sensing a solution feed pressure of said gradient pump; a second pressure sensor for sensing a solution feed pressure of said isocratic pump; and a control unit for computing a difference between the pressure sensed by said first pressure sensor and the pressure sensed by said second pressure sensor, extracting a solution feed pressure of said isocratic pump in accordance with the computed pressure difference, shifting said switching valve such that the solutions fed from said gradient pump are sent to said analytic section with the solution fed from said isocratic pump, and controlling operation of said isocratic pump in match with shift timing of said switching valve such that the solution feed pressure of said isocratic pump approaches at a value of said extracted solution feed pressure.