1.HPLC conditions

a.HPLC column (lot, age, brand)

b.Mobile-phase composition (pH ± 0.05 unit, percent organic ± 2%)

c.HPLC instrument (dwell volume, detection wavelength ± 2 nm, column

temperature ± 5

◦

C, flow rate)

2.Sample preparation

a.Sample solvent (pH ± 0.05 unit, percent organic ± 2%)

b.Sample preparation procedure (shaking time, different membrane filters)

c.HPLC solution stability