Overpressure in nano acquity

Hi all,
I have connected a new nano LC 25 cm, BEH, c18 column, we were in the process of equilibration of the column with the following parameters: flow rate: 0.3 ul/min, with 100% ACN showed a pressure of 4100psi (was done for 10 column volume), with 80:20::ACN:Water showed 5200psi (was done for 10 column volume) and when it was put for 50:50::ACN: Water, it showed an overpressure. Before attaching the column we had done set pressure diagnostics by blocking the analytical inlet which passed the test. 
Please, can anyone help in this regard?


  • Pflan

    May I ask what year you purchased your M-Class?  Older models had a max back pressure of 10k (which a 50:50 ACN: Water mix could be from mathematical calculation).  Newer models max out at 15k.