Nanospray typically involves offline operation in static mode (flow rate ≈ 20 nL/min.) or online using nanobore LC. A third mode,microscale flow injection, has received scant attention due to throughput and carryover limitations. The recent development of reliable nL/min. flow generation coupled with mass-directed variable (parked) flow alleviates these experimental deficiencies.

　　Upon injection, the system operates at a microspray flow rate and automatically decreases to nanospray flow rate when the requisite total ion count (TIC) is detected; upon run completion,high-flow conditions are restored. Post-injection delay time and carryover are minimized by increasing inter-injection wash volume.Signal acquisition at true nanospray flow rates enables extensive characterization by MS/MS for sub-microliter nanoscale injection.