Measurement of melatonin in body fluids: Standards, protocols and procedures

Abstract: The circadian rhythm of melatonin in saliva or plasma, or of the melatonin metabolite 6‐ sulphatoxymelatonin in urine, is a defining feature of suprachiasmatic nucleus function, the endogenous oscillatory pacemaker. These measurements are useful to evaluate problems related to the onset or offset of sleep and for assessing phase delays or advances of rhythms in entrained individuals. Additionally, they have become an important tool for psychiatric diagnosis, its use being recommended for phase typing in patients suffering from sleep and mood disorders. Thus, the development of sensitive and selective methods for the precise detection of melatonin in tissues and fluids of animals emerges as necessary. Due to its low concentration and the co‐existence of many other endogenous compounds in blood, the determination of melatonin has been an analytical challenge. This review discusses current methodologies employed for detection and quantification of melatonin in biological fluids and tissues

1029-1036.qxd

Abstract: A sensitive liquid chromatographic-single quadrupole mass spectrometric method was developed and validated for the determination of lapatinib in human plasma. Following a liquid-liquid extraction with methyl t-butyl ether, lapatinib and isotope labelled lapatinib, used as an internal standard (IS), were separated from the endogenous compounds on a Zorbax SB-C18 (150 ◊ 3 mm, 3.5 µm) column. An isocratic elution with the mobile phase consisting of formic buffer and the mixture of acetonitrile, methanol and formic acid was used. Mass spectrometry with positive electrospray ionization in a single ion monitoring mode was applied. The proposed method provides the satisfactory recovery of lapatinib from human plasma and a sensitivity comparable to numerous tandem mass spectrometric methods, with a lower limit of quantification of 5 ng/mL. The validated method may be applied to pharmacokinetic studies in humans following a single 250 mg oral dose