Variations in bovine milk oligosaccharides after calving using p-aminobenzoic ethyl ester closed-ring labeling and negative ion electrospray LC/MS/MS.

A strategy was proposed to analyze bovine milk oligosaccharides using p-aminobenzoic ethyl ester (ABEE) closed-ring labeling and C18 capillary liquid chromatography negative ion electrospray tandem mass spectrometry. Linkage specific fragment ions were used to identify oligosaccharide isomers. By constructing the mass chromatograms using linkage specific fragment ions, isomers were differentiated based on m/z values as well as temporal separation provided by liquid chromatography.

Gas chromatography electrospray ionization mass spectrometry analysis of trimethylsilyl derivatives.

A method based on the analysis of trimethylsilyl (TMS) derivatives by capillary gas chromatography electrospray ionization mass spectrometry (GC-ESI/MS) was proposed. To improve separation, analytes were derivatized to their TMS derivative. During ESI analysis, TMS derivatives may hydrolyze back to their polar native form and are thus suitable for ESI analysis.

Letter: The formation of a M + 2 compound in the analysis of a trimethylsilyl derivative of monocarboxylic acids by gas chromatography electrospray ionization mass spectrometry.

The trimethylsilyl (TMS) derivative is one of the most widely utilized derivatives for analyzing polar compounds by gas chromatography. An ion two mass units higher than the protonated molecular ion was observed in analyzing TMS-monocarboxylic acids by using gas chromatography electrospray ionization mass spectrometry (GC-ESI/MS). The structure of the M + 2 compound was investigated using tandem mass spectrometry and high-resolution mass spectrometry.

An integrated electrophoretic mobility control device with split design for signal improvement in liquid chromatography-electrospray ionization mass spectrometry analysis of aminoglycosides using a heptafluorobutyric acid containing mobile phase.

Electrophoretic mobility control (EMC) was used to alleviate the adverse effect of the ion-pairing agent heptafluorobutyric acid (HFBA) in the liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) analysis of aminoglycosides. Aminoglycosides separated by LC were directed to a connecting column before their detection via ESI. Applying an electric field across the connecting column caused the positively charged aminoglycosides to migrate toward the mass spectrometer whereas the HFBA anions remained in the junction reservoir, thus alleviating the ion suppression caused by HFBA.

The development of a hydrodynamic flow assisted double junction interface for signal improvement in capillary electrophoresis-mass spectrometry using positively charged nonvolatile additives.

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.

Structural analysis of isomeric chondroitin sulfate oligosaccharides using regioselective 6-O-desulfation method and tandem mass spectrometry.

A strategy based on a regioselective 6-O-desulfation reaction and negative ion electrospray ionization tandem mass spectrometry (ESI-MS(n)) was developed for the structural delineation of isomeric chondroitin sulfate oligosaccharides. Product ions resulting from the glycosidic cleavage provided information about the number of sulfate groups in each sugar residue. After the regioselective 6-O-desulfation reaction, the number of sulfate groups on each residue was obtained using a tandem mass spectrometry analysis of the reaction product.

The development of a counterflow-assisted preconcentration technique in capillary electrophoresis electrospray-ionization mass spectrometry.

A preconcentration approach for CE-MS using counterflow-assisted electrokinetic injection was proposed. The proposed preconcentration method was based on a counterflow-compatible sheathless interface. The interface was fabricated using a capillary-assembled PDMS microdevice that allowed the application of a counterflow and provided liquid-film electrical conduction.

Comparative study of sialyl glycoprotein with multiple glycosylation sites using isotope labeling and capillary liquid chromatography/mass spectrometry.

Rationale: A comparative strategy has been demonstrated using RNase B, a single-site N-linked high-mannose glycoprotein. Glycoproteins are more common with multiple glycosylation sites and with complex glycans. A strategy capable of differentiating the changes caused by glycoprotein concentration, glycosylation site occupancy, and a glycoform profile of complex glycoproteins would be beneficial.

A convenient and sensitive method for haloacetic acid analysis in tap water by on-line field-amplified sample-stacking CE-ESI-MS.

In this study, we propose a simple strategy based on flow injection and field-amplified sample-stacking CE-ESI-MS/MS to analyze haloacetic acids (HAAs) in tap water. Tap water was passed through a desalination cartridge before field-amplified sample-stacking CE-ESI-MS/MS analysis to reduce sample salinity. With this treatment, the signals of the HAAs increased 300- to 1400-fold.

Sheathless capillary electrophoresis electrospray ionization-mass spectrometry interface based on poly(dimethylsiloxane) membrane emitter and thin conducting liquid film.

This study develops a sheathless CE-MS interface using a robust PDMS membrane emitter and liquid-film electric conduction. A 3D mold was constructed for casting the device by using a one-step casting procedure. The interface consisted of a 125 μm-thick triangular emitter with a 50 μm-diameter microchannel, a conducting reservoir, and a 375 μm-diameter channel for assembling the separation capillary.

The development of a sheathless capillary electrophoresis electrospray ionization-mass spectrometry interface based on thin conducting liquid film.

A simple two column sheathless CE/MS interface was constructed using polydimethylsiloxane to fabricate a microdevice allowing facile column alignment and electrical connection. One conducting reservoir, two holes and one 1mm length microchannel between the holes were fabricated on the microdevice. The two holes were used for connecting separation capillary and ESI sprayer.

Estimation of the measurement uncertainty in quantitative determination of ketamine and norketamine in urine using a one-point calibration method.

An approach was proposed for the estimation of measurement uncertainty for analytical methods based on one-point calibration. The proposed approach is similar to the popular multiple-point calibration approach. However, the standard deviation of calibration was estimated externally.

Linkage and branch analysis of high-mannose oligosaccharides using closed-ring labeling of 8-aminopyrene-1,3,6-trisulfonate and p-aminobenzoic ethyl ester and negative ion trap mass spectrometry.

A strategy based on negative ion electrospray ionization tandem mass spectrometry and closed-ring labeling with both 8-aminopyrene-1,3,6-trisulfonate (APTS) and p-aminobenzoic acid ethyl ester (ABEE) was developed for linkage and branch determination of high-mannose oligosaccharides. X-type cross-ring fragment ions obtained from APTS-labeled oligosaccharides by charge remote fragmentation provided information on linkages near the non-reducing terminus. In contrast, A-type cross-ring fragment ions observed from ABEE-labeled oligosaccharides yielded information on linkages near the reducing terminus.

A comparative study of glycoprotein concentration, glycoform profile and glycosylation site occupancy using isotope labeling and electrospray linear ion trap mass spectrometry.

A strategy is presented for comparative analysis of glycoproteins in which the variation of protein concentration, variation of glycosylation site occupancy and variation of glycoform profile can be determined. A comparative study was performed using stable isotope labeling of glycopeptides and peptides by formaldehyde-H(2) and formaldehyde-D(2) and analysis by ESI-MS analysis. The relative intensity of the nonglycosylated peptide provided information about protein concentration variation.

Chiral electrokinetic chromatography-electrospray ionization-mass spectrometry using a double junction interface.

A double junction interface was utilized to preserve separation efficiency and alleviate ion suppression from sulfated β-cyclodextrin (S-β-CD) in electrokinetic chromatography-electrospray ionization-mass spectrometry. The utility of the approach was demonstrated by chiral EKC-MS analysis of dihydroxyphenylalanine and methyldihydroxyphenylalanine enantiomers using either low concentration (counter-migration mode; 0.1% S-β-CD) or high concentration (carrier mode; 2% S-β-CD).

A comparative study of interfaces for microchip micellar electrokinetic chromatography-electrospray ionization mass spectrometry using the surfactant ammonium dodecyl sulfate.

Using ammonium dodecyl sulfate (ADS) as the surfactant, the response of three common interfaces in the direct coupling of microchip micellar electrokinetic chromatography with electrospray ionization mass spectrometry was studied. In the range of 10-40 mM surfactant, a conventional sheath liquid interface provided poorer sensitivity than both sheathless interface and low-sheath-flow interface. At a surfactant concentration <20 mM, a low-sheath-flow interface exhibited less sensitivity than a sheathless interface; however, it outperformed the sheathless interface above a concentration of 20 mM.

Signal enhancement for peptide analysis in liquid chromatography-electrospray ionization mass spectrometry with trifluoroacetic acid containing mobile phase by postcolumn electrophoretic mobility control.

A strategy based on postcolumn electrophoretic mobility control (EMC) was developed to alleviate the adverse effect of trifluoroacetic acid (TFA) on the liquid chromatography-mass spectrometry (LC-MS) analysis of peptides. The device created to achieve this goal consisted of a poly(dimethylsiloxane) (PDMS)-based junction reservoir, a short connecting capillary, and an electrospray ionization (ESI) sprayer connected to the outlet of the high-performance liquid chromatography (HPLC) column. By apply different voltages to the junction reservoir and the ESI emitter, an electric field was created across the connecting capillary.

Fast CEC-MS using poly(dimethylsiloxane) microinjector, short packed column, and low-sheath-flow interface.

A fast CEC-MS approach based on a microinjector and a short CEC column was developed. Poly(dimethylsiloxane) was used as the substrate for microinjector fabrication. A short capillary column (∼5 cm) packed with 5 μm octadecyl silica particles was inserted into the microinjector.

Staggered multistep elution solid-phase extraction capillary electrophoresis/tandem mass spectrometry: a high-throughput approach in protein analysis.

An approach based on staggered multistep elution solid-phase extraction (SPE) capillary electrophoresis/tandem mass spectrometry (CE/MS/MS) was developed in the analysis of digested protein mixtures. On-line coupling of SPE with CE/MS was achieved using a two-leveled two-cross polydimethylsiloxane (PDMS)-based interface. Multistep elution SPE was used prior to CE to provide an additional dimension of separation, thus extending the separation capacity for the peptide mixture analysis.

Sensitivity improvement of CE/ESI/MS analysis of gangliosides using a liquid-junction/low-flow interface.

Methodology is presented which greatly improves the sensitivity of ganglioside analysis by CE/MS without compromising separation efficiency. In this method, non-volatile additives were removed, where possible, to reduce ion suppression. Specifically, alpha-CD, used to break up ganglioside micelle formation, was replaced with isopropyl alcohol.

A liquid-junction/low-flow interface for sensitivity improvement in micelle electrokinetic chromatography-electrospray ionization-mass spectrometry.

A liquid-junction/low-flow interface was used to alleviate ion suppression caused by nonvolatile surfactants in micelle electrokinetic chromatography-electrospray ionization-mass spectrometry. Ion suppression due to micelles was alleviated by adjusting operating conditions to keep micelles from entering the ESI source. Two operation modes were investigated.

The development of a two-leveled two cross interface for on-line coupling solid-phase extraction and capillary electrophoresis-mass spectrometry.

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.

Development of a liquid-junction/low-flow interface for phosphate buffer capillary electrophoresis mass spectrometry.

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.

Chip-CE/MS using a flat low-sheath-flow interface.

A chip-CE/ESI/MS interface based on a low-sheath-flow design has been developed. A flat low-sheath-flow interface was fabricated to facilitate the coupling with a CE microchip. The interface consists of a PMMA reservoir block, a PMMA platform and a replaceable ESI sprayer.

Development of a low-flow multiplexed interface for capillary electrophoresis/electrospray ion trap mass spectrometry using sequential spray.

A multiplexed CE-MS interface using four low-flow sheath liquid ESI sprayers has been developed. Because of the limited space between the low-flow sprayers and the entrance aperture of the ESI source, multichannel analysis is difficult using conventional rotating plate approaches. Instead, a multiplexed low-flow system was achieved by applying an ESI potential sequentially to the four low-flow sprayers, resulting in only one sprayer being sprayed at any given time.