Volumetric absorptive microsampling for targeted metabolomics of whole blood

Volumetric absorptive microsampling (VAMS) enables the collection of small and accurate quantities of biological fluids. Therefore, this sampling technique is of great interest for volume-limited samples or serial collection of samples.
Here, we present and discuss the potential of VAMS for targeted mass spectrometry (MS)-based metabolomics. In total, 24 amino acids and 12 organic acids were selected as target metabolites. Two ultra-high performance liquid chromatography (UHPLC) methods coupled to tandem MS have been developed and optimized for the separation and quantitation of these metabolites. A reversed-phase UHPLC-MS/MS method was used to analyze organic acids, whereas hydrophilic interaction chromatography (HILIC)-MS/MS was selected for the determination of amino acids.
VAMS devices were used to collect 10 µL of whole blood via a simple finger prick. After collection, the samples were dried for two hours before sample preparation. A design of experiments was conducted to find an extraction solvent providing the maximum recovery of the target analytes from the dried VAMS samples. Overall, the optimum extraction solvent was acetonitrile-water in a proportion of 60:40 (v/v), resulting in the detection of all target metabolites in whole blood with good repeatability.
Furthermore, the stability of the analytes in dried whole blood supported on VAMS devices was investigated. We showed that the amino and organic acids were stable for at least 4 days when stored at room temperature. This is in contrast to the instability of these compounds in blood, thereby showing great possibilities of VAMS in metabolomics studies.