Matrix-assisted diffusion-ordered spectroscopy: application of surfactant solutions to the resolution of isomer spectra.

The component spectra of a mixture of isomers with nearly identical diffusion coefficients cannot normally be distinguished in a standard diffusion-ordered spectroscopy (DOSY) experiment but can often be easily resolved using matrix-assisted DOSY, in which diffusion behaviour is manipulated by the addition of a co-solute such as a surfactant. Relatively little is currently known about the conditions required for such a separation, for example, how the choice between normal and reverse micelles affects separation or how the isomer structures themselves affect the resolution. The aim of this study was to explore the application of sodium dodecyl sulfate (SDS) normal micelles in aqueous solution and sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) aggregates in chloroform, at a range of concentrations, to the diffusion resolution of some simple model sets of isomers such as monomethoxyphenols and short chain alcohols.

True chemical shift correlation maps: a TOCSY experiment with pure shifts in both dimensions.

Signal resolution in (1)H NMR is limited primarily by multiplet structure. Recent advances in pure shift NMR, in which the effects of homonuclear couplings are suppressed, have allowed this limitation to be circumvented in 1D NMR, gaining almost an order of magnitude in spectral resolution. Here for the first time an experiment is demonstrated that suppresses multiplet structure in both domains of a homonuclear two-dimensional spectrum.

Matrix-assisted diffusion-ordered spectroscopy: mixture resolution by NMR using SDS micelles.

Diffusion-ordered spectroscopy (DOSY) is a powerful technique for mixture analysis, but in its basic form it cannot separate the component spectra for species with very similar diffusion coefficients. It has been recently demonstrated that the component spectra of a mixture of isomers with nearly identical diffusion coefficients (the three dihydroxybenzenes) can be resolved using matrix-assisted DOSY (MAD), in which diffusion is perturbed by the addition of a co-solute such as a surfactant [R. Evans, S.

Isomer resolution by micelle-assisted diffusion-ordered spectroscopy.

Diffusion-ordered NMR spectroscopy ("DOSY") is a useful tool for the identification of mixture components. In its basic form it relies on simple differences in hydrodynamic radius to distinguish between different species. This can be very effective where species have significantly different molecular sizes, but generally fails for isomeric species.

LC-MS study to reduce ion suppression and to identify N-lactoylguanosine 5'-monophosphate in bonito: a new umami molecule?

In this study a specific taste modulating flavor ingredient, N-lactoylguanosine 5'-monophosphate (N-lactoyl GMP), was determined in bonito (Japanese, Katsuobushi, dried fermented skipjack) and in powdered bonito using liquid chromatography-electrospray ionization (+) mass spectrometry-mass spectrometry (LC-ESI(+)-MS/MS) with a methanol/ammonium acetate or formate gradient. Furthermore, the influence of ion suppression due to sample matrix effect was investigated and was found to substantially influence the total MS response of N-lactoyl GMP; by adjusting the LC conditions the response could be approximately 5-fold-enhanced. The N-lactoyl GMP concentrations in different types of bonito products were between 0.

Identification of N-gluconyl [corrected] ethanolamine in wine by negative electrospray ionization with post-column chloride attachment and accurate mass determination on a triple-quadrupole mass spectrometer.

In this study a specific taste modulating flavour-ingredient, N-gluconyl [corrected] ethanolamine, was determined in two Beerenauslese wines using two different LC-MS techniques. For a first screening LC-MS(2) on an ion-trap mass spectrometer with negative electrospray ionization (ESI(-)) was applied. Sensitivity (and selectivity) was successfully increased approx.

Analysis of functional groups on the surface of plasma-treated carbon nanofibers.

Plasma chemically modified carbon nanofibers were characterized by X-ray photoelectron spectroscopy with regard to the content of carbon, oxygen, and nitrogen and the contribution of carboxylic groups or ester, carbonyl and hydroxylic groups or ether on the surface. Unfortunately, X-ray photoelectron spectroscopy only provides an average value of the first 10 to 15 molecular layers. For comparison, depth profiles were measured and wet chemical methods were applied to estimate the thickness of the functionalized layer and the distribution of oxygen-containing functional groups within the near-surface layers.