(A – C) Extracted ion chromatograms of a standard mixture of dATP, dCTP, dGTP, dTTP, ATP, CTP, GTP, and UTP (5 μM in aqueous solution), using the traditional TEAA ion-paring mobile phase (pH 7.0) with different TEAA concentrations: 5 mM (A), 25 mM (B), and 100 mM (C). (D) Extracted ion chromatogram of a standard mixture of dATP, dCTP, dGTP, dTTP, ATP, CTP, GTP, and UTP (1 μM in aqueous solution), using the TEAA ion-paring mobile phase (pH 7.0) with the TEAA concentration at 100 mM. Chromatographic separation was performed on an Atlantis T3 (2.1× 100 mm, 3 μm) column, under a gradient mobile phase consisting of mobile phase A (TEAA, pH 7.0) and mobile phase B (10% acetonitrile in mobile phase A), with gradient B% (min) as 0 (0) → 60 (6.0) → 0 (6.1) → 0 (10) at a flow rate of 0.5 mL/min.