During the evaluation of the effect of TEA concentration (5-25 mM), pH (4.8-9) of the eluent, and column temperature (5-80 °C), eluent A consisted of milli-Q water with TEAA and eluent B of ACN with TEAA. The gradient started with a 1-min hold at 80% B, followed by a linear decrease of to 66.7% B from 1-21 min, and a hold at 66.7% B for 2 min. The flow rate was 0.2 mL/min. Final conditions for the analysis of mixtures of FLP with impurities were 25 mM TEA in both eluent A and B, an eluent pH of 6.3, and column temperature of 80 °C, applying an 80-66.7% B gradient as mentioned above.