Comparison of hydrodynamic injection and the matrix-switching LC–CE method using two sample injections for multiple peaks: (A) hydrodynamic injection of 11-nL sample 100 μM in each analyte with CE separation; (B) hydrodynamic injection of 33-nL sample 100 μM in each analyte with CE separation; (C) injection of a 20-μL sample 5 μM in each analyte using matrix-switching LC–CE. Conditions for (A) and (B): running buffer, 100 mM lithium acetate, pH 4.75; separation voltage, 18 kV. Conditions for (C): LC buffer, 7.5 mM lithium citrate, pH 2.5/acetronitrile (70:30 v/v); CE buffer, 150 mM lithium acetate, pH 4.75; 80 s stacking time at 22 kV; separation voltage, 18 kV. Peak identities as in Figure 3.