Circadian system coordinates biological processes with the daily rhythmic changes in nature. Since the disruption of the circadian rhythm is a likely player in the aetiology of numerous pathologies, it is crucial that we can reliably measure it. Typically, this involves assessing the daily fluctuations of key circadian biomarkers, namely melatonin and cortisol. Plasma or saliva samples are collected in regular time intervals and their concentrations can be quantified by Liquid Chromatography with Tandem Mass Spectrometry (LC-MS/MS). Here we optimised the LC-MS/MS sample preparation protocol, systematically altering one factor at a time. Simplified protocol was then used to investigate the effect of jet lag on the 24-hour rhythms of melatonin and cortisol. While melatonin exhibited a phase shift consistent with the time difference induced by jet lag, changes in cortisol levels did not enable precise phase shift calculations.
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