Tracking problems and possible solutions in the quantitative determination of small molecule drugs and metabolites in biological fluids using liquid chromatography–mass spectrometry

Analytical Methods for Quantification of Drug Metabolites in Biological Samples

“…LLE sometimes gives better sample clean up showing less matrix effect in comparison with SPE [70]. Additionally, LLE is in general simpler and may be applicable to almost all laboratories using large variety of available solvents.…”

“…Occasionally, due to the nature of dissociation pathways, resulting in low molecular weight product ions, radial ejection preceding dissociation and/or charge stripping, reliable precursor → product ion transitions cannot be established. Alternatively, a precursor → precursor scan for reducing noise can be employed [70].…”

“…The use of other reagents such as formic or acetic acid, trifluoroacetic acid in conjunction with 10 mM ammonium acetate or addition of 1% propionic acid to the mobile phase may overcome the ME of trifluoroacetic acid. Triethylamine may be replaced with other ion paring reagent such as hexylamine [70].…”

“…Optimization of IS concentration is critical to avoid ion suppression by co-eluting analyte leading to standard curve nonlinearity [70]. Even if stable labeled isotope IS is used, ME should still be investigated.…”

“…online SPE) or the analytical column. Most carry-over problems can be minimized by an appropriate choice of injector wash solutions and methods, by proper choice of mobile phase and tubings, and by choice of suitable stationary phase and proper variation in the solvent strength [70]. Carry-over becomes prominent after injection of analyte at high concentration and should be assessed during the validation of the method.…”