Increasingly, untargeted metabolomic studies are being applied to large scale investigations, often comprising several thousands of samples obtained in toxicological, clinical and epidemiological studies. [1,2] Even with the combination of sensitivity, reproducibility and throughput provided by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), there is conflict between the need for rapid analysis and the desire for complete metabolite coverage. Sub 2µm particle liquid chromatography–mass spectrometry (LC-MS-MS) has facilitated a dramatic reduction in analysis time (1-2mins) for high-throughput quantitative analysis, however, transferring this approach to metabolomics studies results in the loss of information and feature detection due to analyte co-elution. [3]

Ion mobility-mass spectrometry (IMS-MS) couples the exquisite sensitivity and structural elucidation properties of accurate mass MS with the novel separation properties of ion mobility. The resulting analytical system allows analyte ions that were chromatographically unresolved to be separated in the ion mobility cell and transferred to the MS detector as discrete ions, thus reducing the interference caused by isobaric species and geometric isomers. While ion mobility cannot address ion suppression resulting from co-elution of ions in the MS source, it can increase the number and quality of peaks detected in the MS system.

Wilson and King recently demonstrated the value of this approach for the analysis of polar metabolites in rat urine formed during a safety assessment study of the diuretic drug tienilic acid. [4] By employing a short 5cm microbore (1mm ID) UPLC column, they were able to reduce the analysis time of the HILIC separation to just 3.5 minutes from 12 minutes for a conventional separation, while maintaining the number of features detected. It was found that the use of IMS-MS almost doubled the number of detected features compared to those detected with MS alone, for the same 3-minute separation. This can be explained by the fact that, for the same separation time, the measured LC peak width was reduced by a factor of 40% when ion mobility was employed. The reduction in LC peak width for the IMS-enabled analysis can likely be attributed to the resolution of co-eluting isobaric metabolites, which can artificially increase the measured peak width.

This methodology has been extended by to the analysis of lipids in biological samples with similarly beneficial results. By employing a short microbore column and elevated flow rates, King and Wilson were able to analyse plasma from breast cancer patients to identify putative biomarkers of disease progression. [5] The use of ion mobility not only enabled the rapid processing of the samples, but provided superior quality spectral MS and MS/MS data, allowing for more accurate database searching.

References

  1. C.L.Gavaghan, E.Holmes, E.Lenz, I.D.Wilson, J.K.Nicholson, N.M.R.An, Based metabonomic approach to investigate the biochemical consequences of genetic strain differences: application to the C57BL101J and Alpk:ApfCD mouse, FEBS Lett. 484 (2000) 169–174. 
  2. J.K. Nicholson, J.C. Lyndon, Nature 455 (2008) 1054.
  3. P.D. Rainville, I.D. Wilson, J.K. Nicholson, G. Isaac, L. Mullin, J.I. Langridge, R.S. Plumb, Ion mobility spectrometry combined with ultra performance liquid chromatography/mass spectrometry for metabolic phenotyping of urine: effects of column length, gradient duration and ion mobility spectrometry on metabolite detection, Anal. Chim. Acta 982 (2017) 1–8. 
  4. King AM, Mullin LG, Wilson ID, Coen M, Rainville PD, Plumb RS, Gethings LA, Maker G, Trengove R. Development of a rapid profiling method for the analysis of polar analytes in urine using HILIC-MS and ion mobility enabled HILIC-MS. Metabolomics. (2019) 22;15(2):17.
  5. King AM, Trengove RD, Mullin LG, Rainville PD, Isaac G, Plumb RS, Gethings LA, Wilson ID. Rapid profiling method for the analysis of lipids in human plasma using ion mobility enabled-reversed phase-ultra high performance liquid chromatography/mass spectrometry. J Chromatogr A. 2019 Oct.