Abstract: A method and system for dispensing a fluid to provide a predetermined weight percent concentration of a sample material to the fluid. An estimated density value for the fluid is used to determine the volume of fluid to dispense in an initial injection of fluid which is less than the total volume of fluid required to achieve the predetermined weight percent concentration. A working fluid density is then determined from the volume of fluid dispensed and a measurement of the weight of the fluid dispensed. The working density is then used to determine the volume of fluid to dispense in a subsequent injection. Preferably, at least three fluid injections are performed, and the working density is determined after each fluid injection.