Chromatographic and Mass Spectrometric Method Development
Instrument Configuration and MS Tuning The majority of contemporary bioanalytical methods employ liquid chromatography-tandem mass spectrometry using a...
Instrument Configuration and MS Tuning
The majority of contemporary bioanalytical methods employ liquid chromatography-tandem mass spectrometry using a triple quadrupole instrument operated in multiple reaction monitoring mode, in which the analytical system comprises an autosampler, liquid chromatography pump, chromatographic column, electrospray ionisation interface, a first mass analyser that selects the precursor ion, a collision cell in which the precursor undergoes controlled fragmentation, and a second mass analyser that monitors specific product ions. Method development begins with infusion-based tuning of a reference standard to establish the optimal ionisation polarity and source parameters, followed by optimisation of the multiple reaction monitoring transitions through selection of the most abundant and selective precursor-to-product ion pairs, with at least two transitions typically monitored for each analyte to provide qualifier and quantifier confirmation.
Column Selection and Mobile Phase Optimisation
Column selection in bioanalytical liquid chromatography is guided by analyte polarity and the desired analysis speed, with sub-two-micrometre octadecylsilane columns of short length representing the most common choice for small molecule drugs owing to their capacity to deliver rapid, high-resolution separations. Phenyl-hexyl stationary phases offer enhanced selectivity for aromatic compounds through pi-pi interactions, hydrophilic interaction liquid chromatography columns are employed for highly polar or ionic analytes poorly retained under reversed-phase conditions, and chiral stationary phases are reserved for the separation of enantiomers of racemic drugs exhibiting stereospecific pharmacokinetics. Mobile phase development involves careful selection of the aqueous-organic ratio, buffer identity, and pH to achieve adequate retention, peak shape, and ionisation efficiency, followed by optimisation of the gradient profile to balance chromatographic resolution against total analysis time.