Patent ID: 6962658

Claim:
A liquid chromatography system having a variable flow rate injector comprising: (a) an injection valve having a sample load position and a sample inject position; (b) a sample source; (c) a microcolumn having an inner diameter of two mm or less in fluid communication with the injection valve; (d) a variable flow rate working fluid supply in fluid communication with the injection valve and the separation column so that when the injection valve is in the sample load position a working fluid can flow into the microcolumn and sample can be placed for injection into the microcolumn, and when the injection valve is in the sample inject position the working fluid displaces placed sample for injection into the microcolumn; and (e) a controller in communication with the variable flow rate working fluid supply and the injection valve for controlling the flow rate of the working fluid, wherein when the working fluid displaces the sample from the injection zone, the working fluid flows at a first flow rate, and after the working fluid displaces the sample, the working fluid flows at a second flow rate and wherein the second flow rate is less than about 100 μl/min; wherein the first flow rate is at least 25% less than the second flow rate.