Cell freeze drying in vacuum. Quenching was used to stop enzymatic activity at ultralow temperatures, whereas drying at low temperature removed water molecules from cells to deactivate enzymes during SCMS measurements under ambient conditions. Freeze drying was performed by placing cold Petri dish (with residual LN2) containing coverslips into a SpeedVac (Thermo Scientific, Savant SPD111V). The rotor of the SpeedVac was removed to accommodate the Petri dish. Cell drying can be accomplished within 5-7 minutes following the standard drying procedures.