Simultaneous Determination of Aromatic, Short-Chain Fatty and Dicarboxylic Acids in Blood Serum and Cerebrospinal Fluid by Gas Chromatography–Mass Spectrometry

Aromatic, short-chain fatty and dicarboxylic acids are low-molecular-weight microbial and mitochondrial metabolites; therefore, their simultaneous screening in biological samples, including cerebrospinal fluid, is a promising solution to an important problem – the timely differential diagnosis of various diseases and pathologies, in particular, those associated with the disruption of the central nervous system. There is a need in developing a sensitive method for the simultaneous determination of these compounds, because they are most often present in biological samples in trace amounts. Blood serum and cerebrospinal fluid are complex matrices including various compounds. Aromatic, short-chain fatty and dicarboxylic acids were isolated and preconcentrated in the present study by traditional liquid–liquid extraction modified at the derivatization stage: the organic extractant was not evaporated and derivatization was carried out directly in the volume of diethyl ether. The different volatilities and polarities of the compounds was taken into account; therefore, derivatization was carried out with moderate heating (60°C) using various silylating reagents. Depending on the type of silyl derivatives, we set the analysis mode of gas chromatography–mass spectrometry method in order to achieve an acceptable analysis time, increase sensitivity to target compounds, and carry out a complete gas chromatographic separation of all analytes. To assess the applicability of the developed conditions, analytical characteristics were determined in model solutions and in the blood serum of healthy donors. For all the developed analysis conditions, linearity was observed in a clinically significant range; the lower limits of quantitation were in the range from 0.06 to 0.9 μmol L–1, which made it possible to analyze samples of the cerebrospinal fluid of neurosurgical patients (n = 6).