Coupling techniques in LC/MS and SFC/MS

Summary Techniques and applications of analytical instruments combining a chromatographic technique, including liquid chromatography and supercritical fluid chromatography, with mass spectrometry (LC/MS and SFC/MS), that have appeared over the past five years, are reviewed and discussed. It is shown that still many different methods co-exist and have both specific advantages and limitations. SFC/MS appears easier to run for many compounds so far analysed by conventional LC/MS methods. On the other hand, new LC/MS methods that use fast atom bombardment or electrospray ionization have the greater potential for the investigation of polar biopolymers.     

Reduction of a quaternary phenanthridinium salt in a chemical ionization source when introduced by direct injection in acetonitrile

Reduction of phenanthridinium methiodide to its dihydroderivative was observed when a solution of the sample in acetonitrile was injected in the chemical ionization source of a combined liquid chromatograph/mass spectrometer equipped with a direct liquid introduction interface and a polarized desolvation chamber.     

Experimental and numerical analysis in heat flow sensors calibration

Journal of Thermal Analysis and Calorimetry - The 2010/31/CE directive has highlighted the necessity to improve the energy efficiency in buildings, since they are responsible for 40% of energy...     

Structural basis for efficient chromophore communication and energy transfer in a constructed didomain protein scaffold

The construction of useful functional biomolecular components not currently part of the natural repertoire is central to synthetic biology. A new light-capturing ultra-high-efficiency energy transfer protein scaffold has been constructed by coupling the chromophore centers of two normally unrelated proteins: the autofluorescent protein enhanced green fluorescent protein (EGFP) and the heme-binding electron transfer protein cytochrome b(562) (cyt b(562)). Using a combinatorial domain insertion strategy, a variant was isolated in which resonance energy transfer from the donor EGFP to the acceptor cyt b(562) was close to 100% as evident by virtually full fluorescence quenching on heme binding. The fluorescence signal of the variant was also sensitive to the reactive oxygen species H(2)O(2), with high signal gain observed due to the release of heme. The structure of oxidized holoprotein, determined to 2.75 ? resolution, revealed that the two domains were arranged side-by-side in a V-shape conformation, generating an interchromophore distance of ～17 ? (14 ? edge-to-edge). Critical to domain arrangement is the formation of a molecular pivot point between the two domains as a result of different linker sequence lengths at each domain junction and formation of a predominantly polar interdomain interaction surface. The retrospective structural analysis has provided an explanation for the basis of the observed highly efficient energy transfer through chromophore arrangement in the directly evolved protein scaffold and provides an insight into the molecular principles by which to design new proteins with coupled functions.     

Post annealing immersion: A new technique for studying rare earth ions in porous materials

A novel technique is introduced for studying how rare earth ions are incorporated into the matrix of porous materials. Tb³⁺-doped silica sol-gel is annealed to form porous glass and immersed in an aqueous Gd(NO₃)₃ solution. Re-heating removes the liquid and deposits Gd³⁺ ions on the internal pore surfaces. Spectroscopic investigation of Gd³⁺→Tb³⁺ energy transfer yields information about the location of Tb³⁺ dopant ions relative to pore surfaces. Results from post-annealing immersion experiments indicate that most Tb³⁺ dopant ions are close to pore surfaces when sol-gel glass is annealed to 700 °C. The observed energy transfer decreases with higher annealing temperatures, indicating that Tb³⁺ dopants in densified regions are isolated from Gd³⁺ ions deposited on pore surfaces. Al³⁺ co-doping affects both the overall sample density and the degree of Gd³⁺→Tb³⁺ interaction in post-annealing immersion samples.     

On-line liquid chromatography/mass spectrometry? An odd couple!

After 7 years of continuous development, LC/MS has attracted considerable attention. Those who have not yet used it believe that LC/MS will solve nearly every analytical problem. The few current users are not so optimistic; instrumental difficulties are still severe, but new techniques are being developed to overcome these.     

Investigation of some vinyl polymers by pyrolysis—gas chromatography—mass spectrometry

Although much has been published on the thermal degradation behaviour and products of vinyl polymers, the possibilities of using gaschromatography—mass spectrometry in the investigation of pyrolysate composition have much to offer.Results for poly(vinyl chloride), poly(vinyl acetate), polystyrene and poly(α-methyl-styrene) homopolymers and styrene—acrylonitrile copolymer obtained by pyrolysis—gas chromatography—mass spectrometry are presented. Numerous additional fragments not previously specified have been determined. The possible mechanisms of their origin as regards the polymer chain structure are discussed.     

Investigation of antioxidants and UV stabilizers from plastics. Part I: Comparison of HPLC and SFC; preliminary SFC/MS study

Synthetic mixtures of additives (antioxidants, UV stabilizers) used in the manufacture of food packaging materials were separated by normal phase HPLC under isocratic or gradient elution, and by capillary SFC using CO₂ as mobile phase. SFC proved to be more efficient for the separation and determination of additives with a wide range of boiling points and for substances lacking a UV chromophoric moiety. Combined SFC/MS, using a direct coupling interface, produced clear charge transfer spectra resembling EI spectra and proton exchange CI spectra when ammonia was added to the ion source.     

GC-MS analysis of cuticular lipids in recent and older scavenger insect puparia. An approach to estimate the postmortem interval (PMI)

An analytical method was developed to characterize puparia cuticular lipids (hydrocarbons, waxes) and to compare the molecular distribution patterns in the extracts from either recent or older puparia. Acid-catalyzed transesterification and solvent extraction and purification, followed by combined gas chromatography coupled to mass spectrometry, were optimized for the determination of hydrocarbons and fatty acid ethyl esters from transesterified waxes, extracted from a single species of a fly scavenger (Hydrotaea aenescens Wiedemann, 1830). Comparison between recent (2012) or older (1997) puparia contents has highlighted significant composition differences, in particular, a general decrease of the chain length in the n-alkane distribution pattern and, on the contrary, an increase of the ester chain length. Both extracts contain traces of three hopane hydrocarbon congeners. Preliminary results evidence the change in puparia lipid composition over time, thus potentially providing new indices for estimating postmortem interval.