Multidimensional Separation of Natural Products Using Liquid Chromatography Coupled to Hadamard Transform Ion Mobility Mass Spectrometry

Recent applications of ion mobility spectrometry in natural product research

Ion mobility spectrometry (IMS) is a rapid separation technique capable of extracting complementary structural information to chromatography and mass spectrometry (MS). IMS, especially in combination with MS, has experienced inordinate growth in recent years as an analytical technique, and elicited intense interest in many research fields. In natural product analysis, IMS shows promise as an additional tool to enhance the performance of analytical methods used to identify promising drug candidates. Potential benefits of the incorporation of IMS into analytical workflows currently used in natural product analysis include the discrimination of structurally similar secondary metabolites, improving the quality of mass spectral data, and the use of mobility-derived collision cross-section (CCS) values as an additional identification criterion in targeted and untargeted analyses. This review aims to provide an overview of the application of IMS to natural product analysis over the last six years. Instrumental aspects and the fundamental background of IMS will be briefly covered, and recent applications of the technique for natural product analysis will be discussed to demonstrate the utility of the technique in this field.

The use of UHPLC, IMS, and HRMS in multiresidue analytical methods: A critical review

Residue chemists who analyse pesticides in vegetables or veterinary drugs in animal-based food are currently facing a situation where there is a requirement to detect more and more compounds at lower and lower concentrations. Conventional tandem quadrupole instruments provide sufficient sensitivity, but speed and selectivity appear as future limitations. This will become an even larger issue when there is a need to not only detect active compounds but also their degradation products and metabolites. This will likely lead to a situation in which the conventional targeted approach must be expanded or augmented by a certain non-targeted strategy. High-resolution mass spectrometry provides such capabilities, but it frequently requires an additional degree of selectivity for the unequivocal confirmation of analytes present at trace levels in highly complex and variable food matrices. The hyphenation of ultrahigh performance liquid chromatography with ion mobility and high-resolution mass spectrometry provides analytical chemists with a new tool for performing such a demanding multiresidue analysis. The objective of this paper is to investigate the benefits of the added ion mobility dimension as well as to critically discuss the current limitations of this commercially available technology.

Untargeted Differential Metabolomics Analysis Using Drift Tube Ion Mobility-Mass Spectrometry

Mass spectrometry-based metabolomics is being increasingly applied to a number of applications, including the fields of clinical, industrial, plant, and nutritional science. Several improvements have advanced the field considerably over the past decade, including ultra-high performance liquid chromatography (uHPLC), column chemistries, instruments, software, and molecular databases. However, challenges remain, including how to separate small molecules that are part of highly complex samples; this can be accomplished using chromatographic techniques or through improved resolution in the gas phase. Ion mobility-mass spectrometry (IM-MS) provides an extra dimension of gas phase separation that can result in improvements to both quantitation and compound identification. Here we describe a typical drift tube IM-MS metabolomics workflow, which includes the following steps: (1) Data acquisition, (2) Data preprocessing, (3) Molecular feature finding, and (4) Differential analysis and Molecular annotation. Overall, these methods can help investigators from a variety of scientific fields use IM-MS metabolomics as part of their own workflow.

Analysis of alkaloids from Peganum harmala L. sequential extracts by liquid chromatography coupled to ion mobility spectrometry

An orthogonal two dimensional analysis method based on high performance liquid chromatography (HPLC) separation and electrospray ionization-ion mobility spectrometry (ESI-IMS) detection was developed for the analysis of alkaloid compounds from Peganum harmala L. seeds. Reverse phase (RP) and hydrophilic interaction chromatography (HILIC) were compared for the most optimal performance using three different chromatographic columns. The experimental results suggest that HILIC mode is a better option for combining with the ESI-IMS system for higher sensitivity and ease in hyphenating. Under optimized conditions, alkaloids from different extraction phases were determined by means of the established HPLC-IMS method. More compounds from Peganum harmala L. seed extracts were differentiated on the HPLC-ESI-IMS system by their retention time and drift time than by HPLC or ESI-IMS alone, and thirteen alkaloids were tentatively identified based on m/z and fragment ions using ultra-high-performance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS). Hence, our results indicate that this method can be considered to be advantageous over traditional absorbance detection methods for resolving complex mixtures because of complementary separation steps, elevated peak capacity, and higher sensitivity.

Correlation ion mobility spectrometry

Using a linearly swept chirp function to modulate a Bradbury-Nielsen (BN) ion gate and application of a common signal processing technique (cross-correlation), we outline a method for obtaining high resolution IMS-MS spectra with ion gate duty cycles approaching 50%. Correlation IMS (CIMS) offers advantages over current multiplexing approaches in IMS-MS, which include the Hadamard and Fourier transforms, by minimizing transform artifacts while maintaining high ion throughput. Although cross-correlation techniques have been utilized previously in the field of IMS, to the best of our knowledge, this approach has not been utilized to obtain spectrum that resembles traditional IMS spectrum with resolving powers approaching the theoretical limit. This new approach relies on a linear sweep, which is a swept frequency signal, commonly utilized in different applications because of its compatibility with the fast Fourier transform (FFT). However, unlike spectra derived from Fourier transformation, CIMS yields data sampling rates that are not dependent upon terminal frequency and takes advantage of several factors unique to IMS operation; the non-linear response of ions at relatively low gate pulse widths, fluctuations in intensity, and peak profiles resembling the input gate pulse vector observed especially noted at low gating frequencies.

Improving the discovery of secondary metabolite natural products using ion mobility-mass spectrometry

Secondary metabolite discovery requires an unbiased, comprehensive workflow to detect unknown unknowns for which little to no molecular knowledge exists. Untargeted mass spectrometry-based metabolomics is a powerful platform, particularly when coupled with ion mobility for high-throughput gas-phase separations to increase peak capacity and obtain gas-phase structural information. Ion mobility data are described by the amount of time an ion spends in the drift cell, which is directly related to an ion's collision cross section (CCS). The CCS parameter describes the size, shape, and charge of a molecule and can be used to characterize unknown metabolomic species. Here, we describe current and emerging applications of ion mobility-mass spectrometry for prioritization, discovery and structure elucidation, and spatial/temporal characterization.

Comparison of linear intrascan and interscan dynamic ranges of Orbitrap and ion-mobility time-of-flight mass spectrometers

RATIONALE

The linear intrascan and interscan dynamic ranges of mass spectrometers are important in metabolome and residue analysis. A large linear dynamic range is mandatory if both low- and high-abundance ions have to be detected and quantitated in heavy matrix samples. These performance criteria, as provided by modern high-resolution mass spectrometry (HRMS), were systematically investigated.

METHODS

The comparison included two generations of Orbitraps, and an ion mobility quadrupole time-of-flight (QTOF) system In addition, different scan modes, as provided by the utilized instruments, were investigated. Calibration curves of different compounds covering a concentration range of five orders of magnitude were measured to evaluate the linear interscan dynamic range. The linear intrascan dynamic range and the resulting mass accuracy were evaluated by repeating these measurements in the presence of a very intense background.

RESULTS

Modern HRMS instruments can show linear dynamic ranges of five orders of magnitude. Often, however, the linear dynamic range is limited by the detection capability (sensitivity and selectivity) and by the electrospray ionization. Orbitraps, as opposed to TOF instruments, show a reduced intrascan dynamic range. This is due to the limited C-trap and Orbitrap capacity. The tested TOF instrument shows poorer mass accuracies than the Orbitraps. In contrast, hyphenation with an ion-mobility device seems not to affect the linear dynamic range.

CONCLUSIONS

The linear dynamic range of modern HRMS instrumentation has been significantly improved. This also refers to the virtual absence of systematic mass shifts at high ion abundances. The intrascan dynamic range of the current Orbitrap technology may still be a limitation when analyzing complex matrix extracts. On the other hand, the linear dynamic range is not only limited by the detector technology, but can also be shortened by peripheral devices, where the ionization and transfer of ions take place.

Adding a new separation dimension to MS and LC-MS: What is the utility of ion mobility spectrometry?

Ion mobility spectrometry is an analytical technique known for more than 100 years, which entails separating ions in the gas phase based on their size, shape, and charge. While ion mobility spectrometry alone can be useful for some applications (mostly security analysis for detecting certain classes of narcotics and explosives), it becomes even more powerful in combination with mass spectrometry and high-performance liquid chromatography. Indeed, the limited resolving power of ion mobility spectrometry alone can be tackled when combining this analytical strategy with mass spectrometry or liquid chromatography with mass spectrometry. Over the last few years, the hyphenation of ion mobility spectrometry to mass spectrometry or liquid chromatography with mass spectrometry has attracted more and more interest, with significant progresses in both technical advances and pioneering applications. This review describes the theoretical background, available technologies, and future capabilities of these techniques. It also highlights a wide range of applications, from small molecules (natural products, metabolites, glycans, lipids) to large biomolecules (proteins, protein complexes, biopharmaceuticals, oligonucleotides).

Ion Mobility Spectrometry - High Resolution LTQ-Orbitrap Mass Spectrometry for Analysis of Homemade Explosives

The detailed chemical characterization of homemade explosives (HMEs) and other chemicals that can mimic or mask the presence of explosives is important for understanding and improving the performance of commercial instrumentation used for explosive detection. To that end, an atmospheric-pressure drift tube ion mobility spectrometry (IMS) instrument has been successfully coupled to a commercial tandem mass spectrometry (MS) system. The tandem MS system is comprised of a linear ion trap and a high resolution Orbitrap analyzer. This IMS-MS combination allows extensive characterization of threat chemical compounds, including HMEs, and complex real-world background chemicals that can interfere with detection. Here, the composition of ion species originating from a specific HME, erythritol tetranitrate, has been elucidated using accurate mass measurements, isotopic ratios, and tandem MS. Gated IMS-MS and high-resolution MS have been used to identify minor impurities that can be indicative of the HME source and/or synthesis route. Comparison between data obtained on the IMS/MS system and on commercial stand-alone IMS instruments used as explosive trace detectors (ETDs) has also been performed. Such analysis allows better signature assignments of threat compounds, modified detection algorithms, and improved overall ETD performance. Graphical Abstract ᅟ.

Mitigation of solvent interference using a short packed column prior to ion mobility spectrometry

This paper introduces a novel approach to overcome the solvent interference in corona discharge-ion mobility spectrometry (CD-IMS) based on the time-resolved signals of the solvent and the analyte. To that end, a short Teflon tube was filled with a low amount of squalene or OV-1, which was prepared and located between the injection port and the entrance of the CD-IMS cell. Through this procedure, a sufficient delay (~5s) was obtained between the introduction of the solvent and the analyte into the reaction region of IMS. This resulted in removing the proton by solvent molecules, as well as increasing the effective collision during the analyte ionization, thereby providing an analysis with more sensitivity, accuracy, and precision. To show the column efficiency, ethion and diazinon (organophosphorus pesticides) were selected as the test compounds and their solutions were analyzed by the proposed method. The amount of sorbent, carrier gas flow rate, and the sorbent temperature affecting the sorbent efficiency were optimized by employing the response surface methodology and the central composite design. The proposed method was exhaustively validated in terms of sensitivity, linearity, and repeatability. In particular, the feasibility of direct injection was successfully verified by the satisfactory results, as compared with those achieved without the prior column. The methodology used in this study is very simple and inexpensive, which can overcome the solvent interference when a solution is directly injected into the CD-IMS.

Structural Analysis of Natural Products

Current mass spectrometry, nuclear magnetic resonance spectroscopy, and X-ray diffraction are presented as structure elucidation tools for analytical chemistry of natural products. Discovering new molecular entities combined with dereplication of known organic compounds represent prerequisites for biological assays and for respective applications as pharmaceuticals or molecular markers. Liquid chromatography is briefly addressed with respect to its use in mass spectrometry- and nuclear magnetic resonance-based metabolomics studies.