Optimization of a direct analysis in real time/time-of-flight mass spectrometry method for rapid serum metabolomic fingerprinting

Abstract

Metabolomic fingerprinting of bodily fluids can reveal the underlying causes of metabolic disorders associated with many diseases, and has thus been recognized as a potential tool for disease diagnosis and prognosis following therapy. Here we report a rapid approach in which direct analysis in real time (DART) coupled with time-of-flight (TOF) mass spectrometry (MS) and hybrid quadrupole TOF (Q-TOF) MS is used as a means for metabolomic fingerprinting of human serum. In this approach, serum samples are first treated to precipitate proteins, and the volatility of the remaining metabolites increased by derivatization, followed by DART MS analysis. Maximum DART MS performance was obtained by optimizing instrumental parameters such as ionizing gas temperature and flow rate for the analysis of identical aliquots of a healthy human serum samples. These variables were observed to have a significant effect on the overall mass range of the metabolites detected as well as the signal-to-noise ratios in DART mass spectra. Each DART run requires only 1.2 min, during which more than 1500 different spectral features are observed in a time-dependent fashion. A repeatability of 4.1% to 4.5% was obtained for the total ion signal using a manual sampling arm. With the appealing features of high-throughput, lack of memory effects, and simplicity, DART MS has shown potential to become an invaluable tool for metabolomic fingerprinting. (J Am Soc Mass Spectrom 2010, 21, 68 -75) © 2010 American Society for Mass Spectrometry M etabolomic fingerprinting, an unbiased, global screening approach to classify samples based on metabolite patterns or "fingerprints", has been performed in a wide variety of biological sample types such as urine, plasma, serum, and tissues [1]. Nuclear magnetic resonance (NMR) and mass spectrometry are two widely used analytical platforms applied to metabolomic fingerprinting. NMR has the advantage of requiring little sample preparation, and of producing datasets that are more easily mined [2-4], but cost and sensitivity are two of its major limitations. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) are two additional techniques commonly used in metabolomic workflows [1,[5][6][7][8][9]. Despite being extremely comprehensive, GC-MS and LC-MS suffer from low analysis throughput and memory effects of the chromatographic supports, particularly when investigating metabolites in biological matrices such as serum. To overcome the above described limitations, enabling technologies for the effective analysis of metabolomes are still rapidly evolving.Direct analysis in real time (DART) is a plasma-based ion generation technique that operates under ambient conditions. It belongs to a wider family of ambient plasma ionization techniques that includes direct atmospheric pressure photo-ionization (DAPPI) [10], direct analysis in real time (DART) [11], flowing atmospheric pressure afterglow (FAPA) [12], plasma-assisted desorption ionization (PADI) [13], desorption atmospheric pre...

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