In this study we show that a nonaqueous capillary electrophoresis mass spectrometry (NACE-MS) method carefully optimized by a design of experiment can be applied to a very large number of alkaloids in different plant extracts. It is possible to characterize the pattern of the psychoactive alkaloids in several plant samples and preparations thereof, each presenting different challenges in their analysis. The method is shown to be able to separate structurally closely related substances, diastereomers and further isobaric compounds, to separate members of different alkaloid classes within one run and to tolerate significant matrix load. A comparison with methods presented in the literature reveals that a near-generic NACE-MS method for the fast profiling of alkaloids in forensically relevant plant samples has been developed.
The consumption of legal and illegal drugs follows an organic trend comparable to the current trend in food consumption. The investigation of such drugs is therefore of interest to characterize the active ingredients of plants and drug preparations. A new method of nonaqueous capillary electrophoresis coupled to mass spectrometry (NACE-MS) as a powerful tool for the separation of complex alkaloid mixtures in difficult matrices is presented in this study for the analysis of samples of Sceletium tortuosum and drug products called Kanna made thereof. The method was found to be suitable for the investigation of the alkaloid composition and relative quantification of the ingredients. It proved of value to separate a large number of isobaric compounds, most probably including diastereomers, double-bond isomers, and further structurally closely related compounds. A comparison of plant samples from different vendors, self-fermented samples, and products ready for consumption was made. The high separation power obtained allowed a better description of the chemotypic differences of plant samples as well as Kanna preparations compared to other methods presented in the literature so far. Thus, the use of the NACE-MS enables a new perspective on the alkaloid profile of Sceletium species.
Non-aqueous capillary electrophoresis (NACE) background electrolytes are most often composed of a mixture of methanol and acetonitrile (ACN) with soluble ammonium salts added as electrolyte. In this study on NACE-MS, we used a mixture of glacial acetic acid and ACN giving rise to an acidic background electrolyte (BGE) with a very low dielectric constant. Impressive changes in selectivity and resolution were observed for structurally closely related indole alkaloids including diastereomers upon addition of ammonium formate as electrolyte and upon variation of the solvent ratio. In order to obtain best separation and MS detection conditions and to reveal the influence of the parameters of the BGE on separation and detection and vice versa of the MS parameters on separation, an optimization strategy was employed using a design of experiments in a central composite design with response surface methodology. It was proven that at high electroosmotic flow conditions capillary electrophoretic separations and thus optimization can be realized without interference from the coupling to an MS system. Several significantly interacting parameters were revealed, which are not accessible with classical univariate optimization approaches. With this optimization, alkaloid mixtures from a plant extract of Mitragyna speciosa, containing a large number of diastereomeric compounds were successfully separated.
In this study, we introduce time-resolved fluorescence detection with two-photon excitation at 532 nm for label-free analyte determination in microchip electrophoresis. In the developed method, information about analyte fluorescence lifetimes is collected by time-correlated single-photon counting, improving reliable peak assignment in electrophoretic separations. The determined limits of detection for serotonin, propranolol, and tryptophan were 51, 37, and 280 nM, respectively, using microfluidic chips made of fused silica. Applying two-photon excitation microchip separations and label-free detection could also be performed in borosilicate glass chips demonstrating the potential for label-free fluorescence detection in non-UV-transparent devices. Microchip electrophoresis with two-photon excited fluorescence detection was then applied for analyses of active compounds in plant extracts. Harmala alkaloids present in methanolic plant extracts from Peganum harmala could be separated within seconds and detected with on-the-fly determination of fluorescence lifetimes.
Electrophoretic separations are of growing interest to tackle complex analytical challenges. Nevertheless, capillary electrophoresis, as the most common mode, still suffers from insufficient detection limits due to low capillary loadability. ITP is of growing interest as preconcentration method for capillary electrophoresis and is also interesting to be applied as an independent analytical method. While mass spectrometric detection is common for capillary electrophoresis, the combination of ITP with MS is still a niche technique. In this work, we want to give an overview on isotachophoretic effects in CE‐MS and ITP‐MS methods, as well as coupling techniques of ITP with CE‐MS. The challenges and possibilities associated with mass spectrometric detection in ITP and its coupling to capillary electrophoresis are critically discussed.
Polycyclic Aromatic Sulfur Heterocycles (PASHs) are undesirable compounds in fuels and refined petroleumbased products. Capillary electrophoresis (CE) was investigated as an alternative to analyze the preisolated PASHs from partially desulfurized materials derived from Athabasca, Canada, bitumen. The sample complexity is considerably reduced by this preisolation by ligand exchange chromatography on a Pd(II) containing phase and subsequent ionization of the neutral PASHs through S-methylation to impart electrophoretic mobility. The PASH components are separated and characterized using CE with a time-of-flight mass spectrometer (TOF MS) as detector. An additional major advantage of the CE separation is that the drawbacks of HPLC (limited separation efficiency) and GC (volatility limitations) for separations of high molecular weight compounds can be circumvented. CE was demonstrated to be a highly efficient method in the separation of PASHs and up to 200,000 theoretical plates were obtained. The practicability of the method was shown by an extensive qualitative analysis of the PASH fraction of a hydrotreated middle distillate and a hydrotreated heavy gas oil. Additional information on the sample composition like the identity of parent ring systems, the alkyl substitution, and hydrogenated products from the hydrodesulfurization was gained through the use of CE-TOF MS and measuring standard PASHs expected to be present. The results are compared with GC-MS and high-resolution Orbitrap measurements of the same samples.
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