So, for the same level of separation power — that is, the same number of theoretical plates (as indicated in Fig. 1), the flow rate on the UHPLC column must be reduced to ~ 0.9 mL/min. At that flow rate the analysis time achieved on the UHPLC column was approximately 70% longer than that on the AFT column. Further, at equal numbers of theoretical plates, the pressure on the 1.9 μm particle packed UHPLC column was 7400 p.s.i. compared to 5300 p.s.i. on the AFT column