Dopamine was analysed with LC-MS/MS equipped with 1290 HPLC (Agilent Technologies, CA, USA), Qtrap 5500 (AB Sciex, MA, USA), and a reverse phase column (Pursuit 5 C18 150 × 2 mm). 3 μl was injected into the LC-MS/MS system and ionized with turbo spray ionization source. 0.1% formic acid in H2O and 0.1% formic acid in methanol were used as mobile phase A and B, respectively. The separation gradient was as follows: hold at 10% B for 5 min, 10 to 70% B for 13 min, 70 to 90% B for 0.1 min, hold at 90% B for 8.9 min, 90 to 10% B for 0.1 min, then hold at 10% B for 2.9 min. LC flow was 200 μl min−1, and column temperature was kept at 23 °C. Multiple reaction monitoring was used in positive ion mode, and the extracted ion chromatogram (EIC) corresponding to the specific transition for each analyte was used for quantitation. The specific transitions (Q1/Q3) for dopamine and internal standard were 154.1/137.1 and 158.1/141.1, respectively. Data was analysed using Analyst 1.5.2 software.
