Multidimensional LC

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This review article summarizes the results obtained from the combined efforts of a joint academic and industrial initiative to solve the real-life challenge of determining low levels of peptide-related impurities in the presence of the related biologically-active peptide at a high concentration.

This month we interview Alexandre Goyon, Senior Scientist in the Small Molecule Pharmaceutical Sciences Organization of Genentech, about his work focused on the online digestion and analysis of RNA molecules using immobilized RNase cartridges attached to a mDLC–MS system, and why the accurate sequencing of sgRNA is important.

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This review article discusses the novel separation and detection strategies that are considered promising in clinical metabolomics to enhance the metabolome coverage. It includes hydrophilic interaction chromatography (HILIC), supercritical fluid chromatography (SFC), multidimensional LC approaches, as well as ion-mobility mass spectrometry (IM-MS) and data-independent acquisition (DIA) analysis methods.

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The evolution of two-dimensional liquid chromatography (2D-LC) instruments along with improved software capabilities has transferred 2D-LC from the hands of experienced researchers to functioning analytical laboratories in the pharmaceutical industry. 2D-LC offers chromatographers novel solutions to problems ranging from analyzing complex samples requiring excessively large peak capacities to separating simple compounds that are difficult to resolve. Recent developments in 2D-LC and 2D-LC–MS have demonstrated the potential of this technique in practice and 2D-LC is set to become an essential tool in the pharmaceutical sector to address problems ranging from coelution, peak purity assessment, simultaneous achiral-chiral analysis, genotoxic impurities, and more.

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Multidimensional chromatography, or comprehensive chromatography, is a well-established technique for the analysis of complex mixtures. However, the technique is often perceived as highly complex and difficult to put into practice for routine applications. Nonetheless, the technique provides exceptional potential for addressing challenging separations. The addition of a dilution factor allows multidimensional chromatography to provide a high level of flexibility and selectivity. The dilution effect is achieved by using a column chemistry format compatible with large flow rates, which now offers the option of large volume injection without volume or mass overload issues. This novel solution can reduce or eliminate the need to add a solvent exchange step, such as evaporation or reconstitution, which significantly reduces the most time-consuming part of the sample preparation process.

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The enhanced separation power of two-dimensional (2D) chromatography has become accessible thanks to the commercialization of dedicated two-dimensional systems. However, with great separation power comes great system complexity. All two-dimensional systems require a means for collecting and transferring fractions of the first dimension to the second dimension typically via a loop-based interface in on-line methods. It is important to collect a sufficient number of fractions to prevent loss of the first dimension resolution; that is, the sampling rate must be sufficient to prevent undersampling. Another key parameter to consider is selectivity. By coupling two selectivities that have unrelated retention mechanisms we are able to exploit the different physiochemical characteristics of the sample we wish to separate. This is the concept behind the term orthogonality. By coupling orthogonal selectivities and reducing under‑sampling, our system should be able to achieve the theoretical maximum two-dimensional peak

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Some members of the separation science community are still not yet convinced of the value of comprehensive two‑dimensional liquid chromatography (LC×LC). They feel that the large increase in separation power (that is, in peak capacity: the number of component peaks that may possibly be separated) may be compromised by losses in sensitivity and robustness of the separation. However, the chairmen of HPLC 2017 will have seen a great number of abstracts come their way from scientists who want to change this perception.

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Comprehensive two-dimensional liquid chromatography (LC×LC) is evolving and becoming more commonly used in practice, but there are some specific problems still present that hamper the widespread use of this technology. One key aspect is the coupling of an on-line LC×LC system to a mass spectrometer. Generally, on-line LC×LC is based on a very fast second dimension separation to achieve low cycle times. This often results in flow rates that are far above the optimum for electrospray ionization mass spectrometry (ESI-MS). This month’s “Multidimensional Matters” looks at the benefits of miniaturization in the first and second dimension for coupling with a high-resolution mass spectrometer (HRMS) and describes an environmental analysis application.