I'm into a RS method development of Piperaquine phosphate. Chromaographic condition is given below. RT of main peak and impurities is shortening as mobile phase become older.(RT shifted from 21 min to 12 min in 10-12 hrs for main peak). My HPLC is in good working condition, repeated the experiment using different reagent bottles.
Mobile phase A= 0.1%Trifluoroacetic acid in water
Mobile phase B= 0.05%Trifluoroacetic acid in mixture of Methanol and Acetonitrile 1:1
Column: inertsil ODS-3 150×4.6mm 3micron
Column temp 40°C
Solutions are prepared in mobile phase A and using a gradient run
Conducted an another trial by replacing methanol from mobile phase B with 0.1% TFA. Result was same.