The IP-RPLC conditions utilized were essentially those according to Rentel et al. Briefly, the eluent was generated by mixing 5 mM TBuAA in ACN-water (10:90, v/v) (A) and 5 mM TBuAA in ACN-water (80:20, v/v) (B) at pH 7, both containing 1 µM EDTA. An Acquity UPLC BEH C18 column (2.1 x 150 mm, 1.7 µm dp, 130 Å) (P/N: 186002353) from Waters was used. The gradient program started with a 1-min hold at 40% B, followed by a linear increase of 40% to 60% B in 20 min. The eluent was held at 60% B for 2 min, followed by a flush to 100% B for 2 min. The flow rate was 0.2 mL/min and the column oven temperature was 60 °C.