Constant pressure mode extended simple gradient liquid chromatography system for micro and nanocolumns

• We extended our simple splitless gradient liquid chromatography system.
• Strain gauge force transducer measures the force applied to the syringe piston.
• We tested the system by gradient separation of the test mixture of nitroesters.
• Faster gradient separations at the constant pressure conditions were realized.
• Identical volume-based chromatograms were obtained at different pressures.

Performing gradient liquid chromatography at constant pressure instead of constant flow rate has serious potential for shortening the analysis time and increasing the productivity of HPLC instruments that use gradient methods. However, in the constant pressure mode the decreasing column permeability during a long period of time negatively affects the repeatability of retention time. Thus a volume-based approach, in which the detector signal is plotted as a function of retention volume, must be taken into consideration. Traditional HPLC equipment, however, requires quite complex hardware and software modifications in order to work at constant pressure and in the volume-based mode. In this short communication, a low cost and easily feasible pressure-controlled extension of the previously described simple gradient liquid chromatography platform is proposed. A test mixture of four nitro esters was separated by 10–60% (v/v) acetone/water gradient and a high repeatability of retention volumes at 20 MPa (RSD less than 0.45%) was realized. Separations were also performed at different values of pressure (20, 25, and 31 MPa), and only small variations of the retention volumes (up to 0.8%) were observed. In this particular case, the gain in the analysis speed of 7% compared to the constant flow mode was realized at a constant pressure.