When the first piston is moving in the second piston is moving out creating a more steady and predictable flow. Click on the above image to view the video. One of the more critical responsibilities of the pumping system is to mix multiple solvents in a consistent and accurate manner. When the HPLC analysis is performed with a non-varying solvent composition, the analysis is said to be done under isocratic conditions. When the HPLC analysis is performed with varying solvent compositions, the analysis is said to be done under gradient elution conditions.
Gradient elution is used to aide in the elution of components with a wide range of polarities.
Gradient elution allows the chromatographer to shorten the HPLC analysis and sharpen the later eluting components. Solvent gradients can be mixed either before the pump has applied pressure or after. Creating the gradient prior to the pumps is less expensive than mixing solvents after the pumps have applied pressure. Mixing the solvent before pressure is applied is less expensive and requires more solvent degassing than systems that mix the solvent on the high pressure side of the pumps. All rights reserved.