Question

HPLC: Look up how an injection valve works and provide sketches of the “load” and “inject” position. Briefly explain the flow of liquid through both positions.

Answer 1

The injection valve is responsible for controlling the flow of eluent through the autosampler device and allows fast and timely delivery of solvent volumes at pressures as high as 7000 psi.

In the LOAD position above, the pump is connected directly to the column inlet. The injection that has the sample solvent is inserted into the sample solvent inlet line and sample is forced out of syringe into the SAMPLE LOOP. After this excess sample is discarded.

Now the seal is rotated into the INJECT position. This is achieved manually by pushing the button of the valve. Alternatively, it is can be done on automatic basis too by the machinery.

In the inject position above, the pump connects to the sample loop and the the mobile phase flows out of the pump, which presses the sample into the column. The injection that hd the sample goes is then discarded.