Electro-kinetic assisted electrospray ionization for enhanced complex sample analysis

Electrokinetic Manipulations Combined With Direct and Ambient Ionization Mass Spectrometry

Mass spectrometry (MS) is a powerful analytical technique that typically involves sample preparation and online analytical separation before MS detection. Traditional methods often face bottlenecks in sample preparation and analytical separation, despite the rapid detection capabilities of MS. This review explores the integration of electrokinetic manipulations directly with the ionization step to enhance MS performance, focusing on methods that eliminate or simplify sample preparation and separation processes. Techniques such as paper spray, electrophoresis in nanoelectrospray ionization (nESI) emitters, induced nESI, counterflow gradient electrofocusing, and in-syringe electrokinetics are highlighted for their ability to combine extraction and ionization in a single step, significantly improving throughput. The review delves into the use of electric fields during sample preparation and separations for these methods, demonstrating the efficiency of electrophoretic methods in driving extractions, crude separations, desalting, and enhanced sensitivity. The integration of these methods directly with MS ionization aims to enhance the analytical capabilities of mass spectrometry, while reducing costs and increasing throughput relative to traditional approaches.

Effect of resolution enhancement using metal ion assisted strategy based on electrospray ionization-ion mobility spectrometry: A case study of carbendazim and thiabendazole in fruits

A method for the rapid and simultaneous determination of carbendazim and thiabendazole residues by electrospray ionization-ion mobility spectrometry (ESI-IMS) combined with a metal ion-assisted technique was developed and validated in different fruit matrices. The metal ion assisted strategy was performed instead of tedious pre-separation procedures to overcome the limitation of low resolution of IMS. Four transition metal cations, Co(II), Ni(II), Cu(II), and Zn(II), were screened and their interactions with carbendazim and thiabendazole were investigated. The injection flow rate and metal ion concentration were optimized. The Cu(II) assisted approach helped to achieve well-separated peaks with a peak-to-peak resolution of 3.61. This method was then applied to detect carbendazim and thiabendazole simultaneously in apples, pears, bananas, and mangoes. The limit of detection (LOD) were 0.03 mg kg-1 and 0.13 mg kg-1 for carbendazim and thiabendazole, respectively, while spiked recoveries were 61.5-122.0% and 83.5-119.8%, respectively, with RSDs less than 13.9%. These satisfactory evaluation parameters indicated that the approach was capable of performing quantitative analysis of multi-pesticide residues. In addition, the feasibility of using metal ion assisted-ESI-IMS for the simultaneous detection also was theoretically demonstrated through molecular electrostatic potential analysis and binding energy calculation based on density functional theory (DFT). Both experimental and theoretical results revealed the effectiveness of the metal ion assisted strategy in improving the resolution of ESI-IMS.

Direct Mass Spectrometry Analysis of Complex Mixtures by Nanoelectrospray with Simultaneous Atmospheric Pressure Chemical Ionization and Electrophoretic Separation Capabilities

Accurate and rapid analysis of complex microsamples are challenging tasks in translational research. Nanoelectrospray ionization (nESI) is the method of choice for analyzing small sample volumes by mass spectrometry (MS), but this technique works well only for polar analytes. Herein, we describe a versatile dual noncontact nESI/nAPCI (nanoatmospheric pressure chemical ionization) source that allows simultaneous detection of both polar and nonpolar analytes in microliter quantities of samples under ambient conditions and without pretreatment. The same device can be activated to enable electrophoretic separation. The noncontact nESI/nAPCI MS platform was applied to analyze different samples, including high sensitive direct analysis of biofluids and the efficient detection of proteins in buffers with high concentration of nonvolatile salts. Excellent linearity, accuracy and limits of detection were achieved for compounds with different chemical properties in different matrices. The high sensitivity, universality, simplicity, and ease of operation make this MS technique promising for use in clinical and forensic applications.

Straight nano-electrospray ionization and its coupling of mobility capillary electrophoresis to mass spectrometry

Mobility capillary electrophoresis (MCE) was developed previously in our group, which has the capabilities of ion separation and biomolecule hydrodynamic radius analysis. The coupling of MCE with mass spectrometry (MS) would greatly improve complex sample identification capability as well as system detection sensitivity. In the present study, a simple and robust ionization source, named as straight nano-electrospray ionization (nanoESI) source was developed, which was applied to couple MCE with MS. A stainless-steel needle attached directly at the end of an MCE capillary was used as the nanoESI emitter, and the connection between this emitter to the liquid flow in the MCE separation channel was established through a liquid bridge. After optimization, this straight nanoESI source enhanced the ion signal intensity by ~10 times when compared with a commercial nanoESI source. The MCE-straight nanoESI-MS system was also characterized in terms of mixture separation and peptide hydrodynamic radius measurements. Compared to our previous work when a UV detector was used in a commercial Lumex CE system (model Capel 105 M, St. Petersburg, Russia), peptides with much lower concentrations could be analyzed (from ~1 mg/mL to ~20 μg/mL) in terms of radius measurement.

Electric modeling and characterization of pulsed high-voltage nanoelectrospray ionization sources by a miniature ion trap mass spectrometer

A better understanding of nanoelectrospray ionization (nano-ESI) would be beneficial in further improving the performances of nano-ESI. In this work, the pulsed high-voltage (HV) nano-ESI has been electrically modeled and then systematically characterized by both voltage-current and mass spectrometry measurements. First, the equivalent resistance of a nano-ESI source changes with respect to both emitter tip diameter and the HV applied. Increased voltage could improve both spray current and ionization efficiency of the pulsed HV nano-ESI. Compared with conventional DC HV method, a pulsed HV has less heating effect on the capillary tip and thus allowing the application of a much higher voltage onto a nano-ESI source. As a result, a pulsed HV nano-ESI could further boost the ionization efficiency of nano-ESI by employing even higher voltages than conventional DC nano-ESI sources.

Recent developments in capillary and microchip electroseparations of peptides (2015-mid 2017)

The review brings a comprehensive overview of recent developments and applications of high performance capillary and microchip electroseparation methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) to analysis, microscale isolation, purification, and physicochemical and biochemical characterization of peptides in the years 2015, 2016, and ca. up to the middle of 2017. Advances in the investigation of electromigration properties of peptides and in the methodology of their analysis (sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, and detection) are described. New developments in particular CE and CEC methods are presented and several types of their applications to peptide analysis are reported: qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC methods to provide important physicochemical characteristics of peptides are demonstrated.