Fig 1.
Chromatograms of blank solvent, OL standard solution, OLM standard solution, and a mixture of OLM and OL standards.
(A) depicts the mobile phase used for the study (50:50 methanol and 0.1% H3PO4 in Mill-Q water). (B) depicts unique OL peak produced by testing of OL 25 μg/mL standard. (C) depicts the unique OLM peak produced by testing the OLM 25 μg/mL standard. (D) depicts both OL and OLM peaks produced by testing the OL/OLM 25 μg/mL standard mixture.
Fig 2.
Standard curves generated from the measurement of OL and OLM present in OL/OLM standard mixtures ranging in concentration from 0.05
μg/ml to 25 μg/mL. (A) depicts the curve of OLM. (B) depicts the curve of OL. These figures validate the linearity of analytical method validation under current ICH guidelines.
Table 1.
Intra- and inter-day precision and accuracy for OLM in QC samples.
Table 2.
Intra- and inter-day precision and accuracy for OL in QC samples.
Fig 3.
Chromatograms of OLM solubility samples in different pH buffers.
OLM and OL were simultaneously detected in the solubility samples, demonstrating the degradation of OLM. Chromatograms were produced from solubility testing of OLM (A) in pH 1.2 buffer, (B) in pH 3.5 buffer, (C) in pH 4.6 buffer, and (D) in pH 6 buffer at 1 hour. Peak identification: (1) peak at 1.5 min is the solvent peak, (2) peak at 3.3 min is the OL peak and (3) peak around 5.5 min is the OLM peak.
Fig 4.
Solubility measurements of OLM in different pH buffers at 1, 2, 3, and 28 hours.
(A) the concentrations of OLM in each buffer over 28 hours. (B) the corresponding concentrations of OL in each buffer over 28 hours.
Fig 5.
Saturated solubility of OLM at different pHs measured at 28 hours.
Table 3.
Parameters of the zero-order kinetic model of OLM hydrolysis to OL in different pH buffers.
Fig 6.
Residual analysis of the linear regression plotting of OLM hydrolysis data with the zero-order kinetic model (A), first-order kinetic model (B), and second-order kinetic model (C).
Fig 7.
Fitting of OLM hydrolysis in different pH buffers at the zero-order kinetic model.