CZE was performed with a CESI 8000 Plus (Sciex) equipped with a Neutral OptiMS capillary cartridge (30 µm ID, L = 90 cm), neutrally coated. The cartridge was washed and conditioned according to the manufacturer's protocols. Separation conditions: Cartridge temperature: 15 ºC, Sample tray temperature: 4 ºC, background electrolyte: 3% HAc, conductive liquid: 3% HAc, hydrodynamic injection: 2.5 psi for 60 s (corresponds to ~20 nL). The individual separation method steps are listed in Table . Overnight, the capillary was rinsed alternating between high flow (100 psi, 2 min)and low flow (10 psi, 120 min) steps with water. For long-term storage, both separation and conductive lines were rinsed (100 psi) with water for 5 min, respectively, and the cartridge was stored at 4 ºC.