Fused silica capillaries were supplied by Polymicro Technologies (Phoenix, AZ, USA). All CE-MS experiments were performed in a 7100 CE coupled with an orthogonal G1603A sheath-flow interface to a 6220 oa-TOF LC/MS spectrometer (Agilent Technologies, Waldbronn, Germany). ChemStation and MassHunter softwares (Agilent Technologies) were used for the CE and TOF mass spectrometer control, data acquisition and processing. The TOF mass spectrometer was operated in ESI+ mode and the optimized parameters are presented in the Supporting Information.
Separations were performed at 25°C in a 72 cm long (LT) × 75 µm i.d. × 365 µm o.d. capillary. All capillary rinses were performed flushing at 930 mbar. For new capillaries or between workdays, the capillaries were flushed off-line with 1 M NaOH (15 or 5 min, respectively), water (15 or 10 min), and BGE (30 or 15 min) to avoid the unnecessary contamination of the MS system. Samples were hydrodynamically injected at 50 mbar for 10 s (54 nL, i.e. 1.7% of the capillary, estimated using the Hagen-Poiseuille equation 35 ), ,and a separation voltage of +25 kV (normal polarity, cathode in the outlet) was applied. The autosampler was kept at 10°C using an external water bath (Minichiller 300, Peter Huber Kältemaschinenbau AG, Offenburg, Germany). Between runs, the capillary was conditioned flushing with water (2 min) and BGE (2 min).
Separations were performed at 25°C in a 72 cm long (LT) × 75 µm i.d. × 365 µm o.d. capillary. All capillary rinses were performed flushing at 930 mbar. For new capillaries or between workdays, the capillaries were flushed off-line with 1 M NaOH (15 or 5 min, respectively), water (15 or 10 min), and BGE (30 or 15 min) to avoid the unnecessary contamination of the MS system. Samples were hydrodynamically injected at 50 mbar for 10 s (54 nL, i.e. 1.7% of the capillary, estimated using the Hagen-Poiseuille equation 35 ), ,and a separation voltage of +25 kV (normal polarity, cathode in the outlet) was applied. The autosampler was kept at 10°C using an external water bath (Minichiller 300, Peter Huber Kältemaschinenbau AG, Offenburg, Germany). Between runs, the capillary was conditioned flushing with water (2 min) and BGE (2 min).