Anal Chem. 2005 Nov 15;77(22):7255-64. Controlled protein precipitation in combination with chip-based nanospray infusion mass spectrometry. An approach for metabolomics profiling of plasma. Boernsen KO1, Gatzek S, Imbert G. Abstract

Liquid chromatography-mass spectrometry (LC-MS) is a common method for profiling biological samples in metabolomics. However, LC-MS data of metabolomic studies are often affected by high noise levels, retention time shifts, and high variability in signal intensities. With a new chip-based nanoelectrospray source it becomes possible to directly infuse complex biological samples such as plasma without any chromatographic separation beforehand. In combination with highly diluted samples and long data acquisition times, the parallel analysis of hundreds of compounds is now possible. In a proof-of-concept study, 10 human plasma samples from females and males were analyzed with the intention to separate the two groups by their different metabolomes. The reproducibility was so high that statistical analysis of the data could be performed without prior normalization. Two groups of female and male samples were separated by a supervised machine learning algorithm, principal component analysis, and hierarchical clustering. Peaks contributing to the group separation were characterized by accurate mass measurement and MS-MS fragmentation and by spiking experiments. The feasibility of direct sample infusion using the new chip-based nanoelectrospray device opens a new dimension for the rapid parallel analysis of complex biological mixtures.

Mass Spectrometer. For all analyses, an orthogonal hybrid quadrupole time-of-flight mass spectrometer (QTOF-Ultima, Mi-cromass, Manchester U.K.) was used. All instrument settings were optimized for the mass range 100 - 3000 m/z to provide a mass resolution of 9000 fwhm. To keep the inlet system clean, cone gas  was  used  with  a  flow  rate  of  200  L/h.  The  source  block temperature was set to 60 °C. For chip-based nanoelectrospray, the  Nanomate  100  (Advion)  was  attached  to  the  QTOF.