High performance liquid chromatography

HPLC was performed using an Agilent model 1100 system (Agilent, Santa Clara, CA) with a variable wavelength detector and a β-RAM-LS radioactivity detector (IN/US Systems; Tampa, FL) with a 500-μL lithium glass, flow-through, solid-flow cell or a 500-μL liquid cell.

The column used was a Microsorb 100–5 silica column (250 × 4.6 mm, Varian; Palo Alto, CA). Mobile phase [acetonitrile:water:ethanol:acetic acid:0.83 M ammonium acetate (0.78:0.14:0.07:0.04:0.007, v/v, pH 3.6)] was used in isocratic conditions at a flow rate of 2.7 mL/min. [¹⁴C]choline eluted at 3.6 min.

The column used was a Phenomenex Luna C18 column (150 × 4.6 mm, 5 μm; Torrance, CA). Mobile phases A [potassium phosphate:sodium heptanesulphonate:tetramethylammonium chloride (0.05 M:0.025 M:0.0025 M, pH 3.0)] and B (acetonitrile) were used with a gradient run from 0% B to 10% B over 10 min, then to 95% B over 20 min at a flow rate of 1.0 mL/min. [¹⁴C]choline was eluted at 8.1 min. [¹⁴C]DMAE eluted at 8.8 min.

The column, mobile phases and flow rate used were the same as in Method B, except that a gradient was run from 0% B to 10% B over 15 min, then to 30% B over 10 min at a flow rate of 1.0 mL/min.

The column used was a Phenomenex Luna C18(2) column (150 × 2.0 mm, 3 μm; Torrance, CA). Mobile phases A (0.1% formic acid in water) and B (0.1% formic acid in acetonitrile) were used with a gradient run from 5% B, held for 1.5 min, to 60% B at 7 min at a flow rate of 0.2 mL/min.