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To alleviate signal suppression resulting from nonvolatile positive ion additives, a hydrodynamic flow assisted double junction capillary electrophoresis-mass spectrometry (CE-MS) interface was proposed. The double junction interface which could alleviate the ion suppression due to nonvolatile negative ion additives was modified so that a hydrodynamic flow could be introduced to the interface. Using this setup, the apparent velocity of the ions was determined based on its electrophoretic mobility, electroosmotic flow in the transfer capillary, and hydrodynamic flow introduced by the syringe pump. CE-MS analysis of positively charged triazines was performed to demonstrate the practical value of this approach by using cetyltrimethylammonium ion (CTA(+)) as an additive. Because the separation column was dynamically coated with CTA(+), the EOF was reversed and the separation was performed under counter EOF mode. Under an appropriate hydrodynamic flow, the analytes (triazines) could be propagated toward the MS, whereas the additive (CTA(+)) ion was retained in the interface. Consequently, the problem of signal suppression by CTA(+) was alleviated, and the signals were enhanced more than 20-fold., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A two-leveled, two cross PDMS-based interface for on-line coupling of SPE with CE-MS was proposed. In this interface, the SPE column and the CE separation column were positioned orthogonally and two crosses were fabricated on the interface. With the two cross design, the operation of SPE could be performed independently without unexpected flow through leakage into the separation column. The performance of the interface was optimized using a peptide mixture. The position of the SPE column related to the CE separation channel was found to be critical to the performance of the system. Under the optimal position, the separation efficiency was similar to a CE-MS experiment without SPE. The peptide signals were enhanced 50- to 100-fold and the repeatability was within 4% RSD for migration time and 10% RSD for peak area. A tryptic digest of cytochrome c was used to demonstrate the feasibility of the interface in protein identification at a level of 1 ng/microL.

To alleviate ion suppression from phosphate buffer and to preserve separation integrity, a new capillary electrophoresis mass spectrometry (CE-MS) interface was developed. The interface consisted of a low-flow interface and a liquid junction. In this design, both the inlet reservoir and the liquid-junction reservoir were filled with phosphate running buffer. Because the phosphate anions in the column migrated toward the inlet reservoir (away from the electrospray ionization (ESI) source) the problem of ion suppression in ESI was avoided. The liquid junction was incorporated to eliminate issues of degraded separation observed when sheath liquid interfaces use different buffers for separation and MS analysis attributed to differences in anion velocity. The utility of the interface was demonstrated by the analysis of antihistamines at pH 3.5 and the analysis of perfluorocarboxylic acid at pH 9.5.

Abstract: To avoid problems associated with the use of sintered frits to retain packing material, tapered columns were investigated for use with capillary electrochromatography–mass spectrometry (CEC-MS) analysis. Taking the advantage that negatively charged stationary phase particles have a net velocity directed towards the buffer reservoir (inlet) over a wide range in pH, a fritless CEC column with a single taper tip was prepared for CEC-MS analysis. During CEC-MS analysis, the tapered end was immersed in the buffer reservoir and the unmodified end was pointed toward the ionization source. For better sensitivity, this single tapered CEC column was coupled to ESI/MS using a low flow sheath liquid interface. With this setup, occasional blockage of the ESI sprayer by stationary phase particles was observed. In addition, significant dead volume was observed because the unmodified tip could not be inserted into the very end of the sprayer of the low flow sheath liquid interface. To circumvent these problems, a dual tapered CEC column was prepared. This fritless dual tapered column CEC-MS approach alleviated the problems of frit, sprayer blockage and extensive dead volume. [Copyright &y& Elsevier]

A method based on sequential degradation, p-aminobenzoic ethyl ester (ABEE) closed-ring labeling, and negative ion electrospray ionization tandem mass spectrometry is presented for the study of linkage and branch determination for N-linked oligosaccharides. Closed-ring labeling provides greater linkage information than the more popular open-ring reductive amination approach. In addition, after high-performance liquid chromatography (HPLC) separation, closed-ring labeling allows for regeneration of the underivatized oligosaccharide, a requirement for alkaline sequential degradation. The analytical scheme presented here uses HPLC separation of closed-ring labeled oligosaccharides to resolve the mixture into individual forms that undergo subsequent structural analysis by negative ion tandem mass spectrometry. To facilitate complete structural analysis, particularly for larger sugars, the closed-ring labels are removed and the sugars are sequentially degraded by controlled alkaline hydrolysis. It is noteworthy that for sugars containing sialic acid moieties, a protecting group must be used to stabilize sialic acid groups during sequential alkaline degradation. This described approach was applied to two high mannose oligosaccharides M5G2, M6G2 cleaved from the ribonuclease B and a complex oligosaccharide A2 cleaved from transferrin. [Copyright &y& Elsevier]

A robust interface has been developed for interfacing micellar electrokinetic chromatography (MERE) and non-volatile buffer capillary electrophoresis (CE) to electro- spray ionization mass spectrometry (ESI-MS). The interface consists of two parallel capillaries for separation (50 μm i.d. × 155 μm o.d.) and makeup (50 μm i.d. × 155 μm o.d.) housed within a larger capillary (530 μm i.d. × 690 μm o.d.). The capillaries terminate in a single tapered tip having a beveled edge. The use of a tapered beveled edge results in a greater tip orifice diameter (75 μm) than in a previous design from our laboratory (25 μm) that used a flat tip. While maintaining a similar optimum flow rate and consequently similar sample dilution, a 75-μm beveled emitter is more rugged than a 25-μm flat tip. Furthenuore, the incorporation of a sheath liquid capillary allows the compositions of the final spray solution to be controlled. The application of this novel CE/ESI-MS interface was demonstrated for MEKC using mixtures of triazines (positive ion mode) and phenols (negative ion mode). The ability to perform CE/ESI-MS using a non- volatile buffer was demonstrated by the analysis of gangliosides with a buffer consisting of 40 mM borate and 20 mM α-cyclodextrin. [ABSTRACT FROM AUTHOR]