The effects of modifiers on electrospray ionization for small-to-medium-sized molecules in comparison with solution-phase ionization.

Modifiers are essential additives in electrospray ionization (ESI) mass spectrometric analysis to enhance the production of ionic species in the gas phase for the detection of small-to-medium-sized molecules in biological and aqueous samples. Therefore, an appropriate modifier, in conjunction with the right ionization polarity, is crucial for sensitive ESI mass spectrometric analysis. However, the charge carried by basic and acidic functional groups in solution is neither quantitatively nor qualitatively reflected in the MS spectrum.

Pancreatic beta cell regenerative potential of Zanthoxylum chalybeum Engl. Aqueous stem bark extract.

Ethnopharmacological Relevance: Zanthoxylum chalybeum Engl. is endemic to Africa and has been used traditionally to treat diabetes mellitus. Moreover, its pharmacological efficacy has been confirmed experimentally using in vitro and in vivo models of diabetes.

Evaluating the "wrong-way-round" electrospray ionization of antiretroviral drugs for improved detection sensitivity.

The presence of antiretroviral drugs (ARVDs) in the aquatic environment poses a significant health risk to the ecosystem. The dilution of these compounds during wastewater treatment processes, followed by discharge into the environment, results in extremely low concentrations in the range of ng/L. Therefore, to enable detection of these low concentrations, it is important to determine the most efficient electrospray ionization (ESI) mode using the right mobile phase modifier and to establish a selective extraction procedure.

Comprehensive analysis of chestnut tannins by reversed phase and hydrophilic interaction chromatography coupled to ion mobility and high resolution mass spectrometry.

In this study, we report a methodology based on reversed phase LC (RP-LC) and hydrophilic interaction chromatography (HILIC) separations coupled to ion mobility (IM) and high resolution mass spectrometry (HR-MS) for the detailed analysis of hydrolysable tannins. The application of this approach to the analysis of an industrial chestnut (Castanea sativa, wood chips) tannin extract is demonstrated. A total of 38 molecular species, including a large number or isomers, were identified in this sample based on HR-MS and UV absorption spectral information as well as retention behaviour in both separation modes.

Comprehensive analysis of tara tannins by reversed-phase and hydrophilic interaction chromatography coupled to ion mobility and high-resolution mass spectrometry.

Reversed-phase liquid chromatography (RP-LC) and hydrophilic interaction chromatography (HILIC) methods hyphenated to diode array detection and ion mobility (IM) high-resolution mass spectrometry (HR-MS) were used for the analysis of gallic acid derivatives and gallotannins in a commercial tara extract. UV spectra combined with low and high-collision energy mass spectral data and known RP-LC elution orders allowed the identification of 45 isomeric gallic acid derivatives and gallotannins. The synergy between IM and UV data was found to provide a simple means to determine the number of depsidic bonds and thus to distinguish between positional isomers.

Comprehensive Three-Dimensional LC × LC × Ion Mobility Spectrometry Separation Combined with High-Resolution MS for the Analysis of Complex Samples.

Comprehensive two-dimensional liquid chromatography (LC × LC) and ion mobility spectrometry-mass spectrometry (IMS-MS) are increasingly being used to address challenges associated with the analysis of highly complex samples. In this work, we evaluate the potential of the combination of these techniques in the form of a comprehensive three-dimensional LC × LC × IMS separation system. As application, hydrophilic interaction chromatography (HILIC) × reversed phase LC (RP-LC) × IMS-high-resolution MS (HR-MS) was used to analyze a range of phenolic compounds, including hydrolyzable and condensed tannins, flavonoids, and phenolic acids in several natural products.

Recent advances and trends in the liquid-chromatography-mass spectrometry analysis of flavonoids.

Flavonoids have elicited significant attention as a result of their importance in plants, their influence on the properties of natural-product derived commodities and especially as a consequence of their purported health benefits. Research in all of these fields relies heavily on accurate analytical data, and in this LC-MS has come to play an influential role by allowing relatively fast tentative identification and accurate quantification of low levels of flavonoids in a variety of matrices. The field has undergone rapid expansion in the last decade due to important developments in both HPLC and MS instrumentation, which nowadays allow much faster and more accurate analysis of flavonoids.

Is there a fundamental 300 Hz limit to pulse rate discrimination in cochlear implants?

Literature often refers to a 300 pps limit for cochlear implant (CI) electrical stimulation, above which pulse rate discrimination deteriorates or above which rate pitch is not perceived to increase. The present study investigated the effect on pulse rate difference limens (PRDLs) when using compound stimuli in which identical pulse trains were applied to multiple electrodes across the length of the electrode array and compared the results to those of single-electrode stimuli. PRDLs of seven CI users were determined in two stimulus pulse phase conditions, one in which the phase delays between pulses on different electrodes were minimised (burst mode) and a second in which they were maximised (spread mode).

Analysis of commercial proanthocyanidins. Part 3: the chemical composition of wattle (Acacia mearnsii) bark extract.

Wattle (Acacia mearnsii) bark extract is an important renewable industrial source of natural polymers for leather tanning and adhesive manufacturing. The wattle bark proanthocyanidin oligomers have 5-deoxy extender units that render the interflavanyl bonds resistant to acid catalysed hydrolysis and their composition cannot be determined via conventional thiolysis. We combined established phyto- and synthetic chemistry perspectives with an electrospray mass spectrometry investigation to establish that the flavan-3-ol based oligomers consist of a starter unit which is either catechin or gallocatechin, angularly bonded to fisetinidol or predominantly robinetinidol extender units.

Analysis of commercial proanthocyanidins. Part 2: An electrospray mass spectrometry investigation into the chemical composition of sulfited quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood extract.

Proanthocyanidins (PACs) are natural plant-derived polymers used in leather tanning, wood adhesives, water purification, and mud additives for oil drilling. Quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood and mimosa (Acacia mearnsii) bark extracts are the major industrial sources of PACs. These commercial extracts are often sulfited via treatment with sodium hydrogen sulfite to reduce their viscosity and increase their solubility in water.

Analysis of commercial proanthocyanidins. Part 1: the chemical composition of quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood extract.

Quebracho (Schinopsis lorentzii and Schinopsis balansae) extract is an important source of natural polymers for leather tanning and adhesive manufacturing. We combined established phyto- and synthetic chemistry perspectives with electrospray mass spectrometry experiments to prove that quebracho proanthocyanidin polymers consist of an homologous series of flavan-3-ol based oligomers. The starter unit is always catechin which is angularly bonded to fisetinidol extender units.