Sheathless capillary electrophoresis‐mass spectrometry using a pulsed electrospray ionization source

Chao, Bing-Fong; Chen, Chao‐Jung; Li, Fu An; Her, Guor‐Rong

doi:10.1002/elps.200500811

Cited by 16 publications

(16 citation statements)

References 37 publications

(36 reference statements)

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“…To avoid this, a pulsed electrospray method has been proposed (59). In this report, the separation capillary was tapered to 30 μm and coated with a conductive rubber.…”

Section: Detectionmentioning

confidence: 99%

Capillary Electrophoresis in Bioanalysis

2008

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Science reports ∼4800 hits on capillary electrophoresis (CE) including 410 reviews. Because of the prominence of CE techniques in bioanalysis, we decided make them the focus of this review and selected 200 hundred papers representing advances in this field. The selected papers cover advances in CE theory, instrumentation, and methodologies that are specific to various analytes of biological origin or relevance. The group of analytes includes nucleic acids, proteins and peptides, carbohydrates, lipids, single cells, and bioparticles. In addition, we have included advances in the use of CE to define functional assays or to investigate biomolecular interactions. The use of microfabricated devices for CE analysis was not included because this is already covered in other review. Technique Developments Separation SchemesDetermining the velocity of the electroosmotic flow (EOF) and how it changes during an electrophoretic separation is still an important research topic. A simple method for EOF measurements using so-called thermal marks was reported (1). Here, a tungsten filament caused punctual heating at the capillary wall and caused a perturbation in the electrolyte concentration. A sequence of these "thermal marks" then migrated with the EOF until each mark reached and was detected by a conductivity detector. The feasibility of using thermal marks as internal EOF standards in different separation systems was thereby demonstrated.Isoelectric focusing separates amphoteric analytes such as proteins or peptides by the differences in their isoelectric points. Most of the reports on capillary isoelectric focusing (cIEF) describe an initial focusing phase after which the focused zones are mobilized and detected. A dynamic cIEF method for protein analysis was reported (2). This technique made it possible to control each protein's position and focused width by moving the pH gradient within the capillary through manipulation of the electric fields. An important advantage of this approach is the capability of collecting focused analytes from the central section, suggesting that there may be great potential for introducing selectively focused proteins to a second separation dimension such as LC or CE.Micellar electrokinetic capillary chromatography (MEKC) is typically incompatible with electrospray mass spectrometry (ESI-MS) because the nonvolatile surfactants in the micellar phase result in complicated adduct formation and loss of sensitivity during the electrospray process and because the presence of the organic solvent needed for electrospray may cause instability in the micellar phase. These drawbacks were overcome by using synthetic polymeric surfactants that can work as a pseudostationary phase and provide stable electrospray (3). The polymeric surfactant was made by polymerizing three amino acidderived (L-leucinol, L-isoleucinol, L-valinol) sulfated chiral surfactants. These polymeric

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“…To avoid this, a pulsed electrospray method has been proposed (59). In this report, the separation capillary was tapered to 30 μm and coated with a conductive rubber.…”

Section: Detectionmentioning

confidence: 99%

Capillary Electrophoresis in Bioanalysis

2008

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“…For commonly used capillaries with 50 μm i.d., the EOF is about 50-250 nL/min. [20] In a sheath flow ESI interface, the optimal flow rate of 50 μm i.d. capillary without tapering is about 4-5 μL/min, which is much higher than the EOF in CE separation capillary.…”

Section: Methodsmentioning

confidence: 99%

“…capillary without tapering is about 4-5 μL/min, which is much higher than the EOF in CE separation capillary. [20] However, analytes would be greatly diluted by the sheath liquid which results in lower sensitivity. Thus, to maintain the sensitivity of CE, a sheathless interface is always preferred.…”

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confidence: 99%

“…capillary used in the sheathless design, the optimal ESI flow rate is about 500-700 nL/min which is obviously too high to match the EOF in CE. [20] To meet the flow rate requirement, pressure-assisted capillary electrophoresis [18,21] has been developed. However, the extra pressure would change the flat flow (major reason to maintain high separation efficiency for CE) into laminar flow, which may broaden the peaks and reduce the separation efficiency.…”

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confidence: 99%

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Sheathless interface to match flow rate of capillary electrophoresis with electrospray mass spectrometry using regular‐sized capillary

Yin

Guan

et al. 2016

Rapid Comm Mass Spectrometry

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RATIONALE:The flow rate match has been a great challenge when coupling capillary electrophoresis (CE) with electrospray ionization mass spectrometry (ESI-MS). Conventional CE-ESI-MS interfaces used liquid sheath flow, narrowed capillary or additional pressure to meet this requirement; sacrifice of either capillary inner diameter (i.d.) or separation efficiency is often inevitable. Thus, a regular-sized capillary-based sheathless interface would be attractive for flow rate match in CE-MS. METHODS:The regular-sized capillary-based CE-MS interface was achieved by coupling CE with induced electrospray ionization (iESI) which was stimulated by the fact that the iESI could both achieve flow rate down to 0.2 μL/min and retain ionization efficiency. The CE-iESI-MS interface was completed with an intact separation capillary, outside the outlet end of which a metal electrode was attached for the application of alternating current (ac) high voltage (HV). RESULTS: The feasibility of this CE-iESI-MS interface was demonstrated through the stable total ion chromatograms obtained by continuous CE infusion of tripropylamine with regular-sized capillaries. Tripropylamine and atenolol were separated and detected successfully in phosphate buffer solution (PBS) by CE-iESI-MS using a 50 or 75 μm i.d. capillary. Furthermore, this new interface showed a better signal-to-noise (S/N) of 3 to 7 times enhancement compared with another sheathless CE-ESI-MS interface that using one high voltage for both separation and electrospray when analyzing the mixture of tripropylamine and proline in NH 4 OAc buffer. In addition, the reproducibility of this interface gave satisfactory results with relative standard deviation (RSD) in retention time in the range between 1% and 3%. CONCLUSIONS: The novel sheathless CE-MS interface introduced here could match conventional electroosmotic flow (EOF) with electrospray which could also preserve the separation efficiency and sensitivity of CE-MS. This newly developed CE-iESI-MS interface was also demonstrated to be effective for different buffers, PBS and NH 4 OAc, without any additives such as methanol and acetic acid. Hence, we believe that this sheathless CE-MS interface could be operated with other nonvolatile and volatile buffers. Copyright © 2016 John Wiley & Sons, Ltd.The combination of capillary electrophoresis (CE) and mass spectrometry (MS) [1][2][3] has become a powerful technique for separation and detection of a broad range of compounds since it was introduced in the late 1980s. [4] To date, electrospray ionization (ESI) has been the most frequently used interface for CE-MS coupling. However, there are two major challenges when interfacing CE with ESI-MS. One is to maintain a constant electrical contact for both CE separation and the ESI process. A sheath or make-up flow [5][6][7] can be used to mix with the CE effluent at the outlet to establish the electrical contact. While for sheathless interfaces the electrical contact was established by direct application of high voltage (HV) via a conductiv...

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“…Like ESI, which was recently developed in pulsation mode with mass spectrometry [77][78][79][80], EDI can operate in continuous and pulsing modes. The pulsing of EDI is controlled by adjusting the applied EDI voltage relative to the sample flow rate [4].…”

Section: Introductionmentioning

confidence: 99%