Impact of malolactic fermentation on low molecular weight phenolic compounds

A reversed phase liquid chromatography-DAD method is proposed for analysis of major non-flavonoid phenolic compounds in wines. The method employed a mixture of acetic acid, water and methanol as eluents and was used to evaluate the impact of malolactic fermentation in low molecular phenolic compounds.

The wines analyzed underwent different treatments, like the addition of a pectolytic enzyme or lysozyme, and the way malolactic fermentation was carried out—spontaneously or with the inoculation of two different commercial lactic bacteria.

The main result observed was the disappearance of hydroxycinnamoyltartaric acids and the increase of resultant free forms, regardless the way malolactic fermentation was carried out.     

Design and evaluation of a multi-detection system composed of ultraviolet, evaporative light scattering and inductively coupled plasma mass spectrometry detection for the analysis of pharmaceuticals by liquid chromatography

Reversed-phase liquid chromatography was coupled to a multi-detection system composed of ultraviolet (UV) detection, evaporative laser scattering detection (ELSD) and inductively coupled plasma mass spectrometry (ICP-MS). By applying the principle of post-column solvent compensation, the organic modifier content was kept constant in ELSD and ICP-MS under gradient elution. Chlorine ((35)Cl), bromine ((79)Br and (81)Br) and sulfur ((34)S) were monitored in several pharmaceutical compounds. The limit of quantitation (LOQ) was 80 ng/mL for chlorine (chlorpropamide) and 2 ng/mL for bromine (bromazepam). Calibration graphs were linear from 1.0 microg/mL to 100 microg/mL for chlorpropamide (r(2) 0.990) and from 10 ng/mL to 500 ng/mL for bromazepam (r(2) 0.996). The low LOQ value for bromine allows to quantify bromine in pharmaceutical samples below the 0.05% level of the active pharmaceutical ingredient.     

Creating a fatty acid methyl ester database for lipid profiling in a single drop of human blood using high resolution capillary gas chromatography and mass spectrometry

Capillary gas chromatography (CGC) in combination with mass spectrometry (MS) was optimized for the separation and detection of the fatty acids occurring in the lipid fraction of blood. A fingertip blood sample (ca. 50 microL) was transesterified into the methyl esters and analyzed on a 100 m x 0.25 mm ID column coated with a biscyanopropyl polysiloxane (HP-88) stationary phase. The method was retention time locked. Programmed temperature vaporization injection (PTV) in the solvent venting mode was applied to minimize the sample size, while maintaining high sensitivity. The total analysis time was ca. 60 min. Retention times and both electron impact (EI) and positive chemical ionization (PCI) mass spectrometry were combined to elucidate the fatty acids according to alkyl chain, degree of unsaturation and position of the double bonds. Using extracted ion chromatograms about 100 fatty acids and related compounds were detected in blood samples and most of them were identified. This work resulted in a very large fatty acid methyl esters database, containing retention time and mass spectral information that will be applied to metabolomic studies.     

Comparison of one-dimensional and comprehensive two-dimensional separations by gas chromatography

Comprehensive two-dimensional gas chromatography (GC x GC) can reveal information on the composition of a sample in a way that cannot be done by one-dimensional GC (1D-GC). GC x GC also offers much greater control of chromatographic selectivity based on molecular structure. However, in spite of more than 15 years of claims of the ability of GC x GC to resolve an overwhelmingly larger number of peaks than 1D-GC, and in spite of the theoretically proven potential of GC x GC to have an order of magnitude larger peak capacity than 1D-GC, the peak capacity of currently practiced GC x GC does not generally exceed the peak capacity attainable from 1D-GC with the same analysis time and the same minimal detectable concentration (MDC). The methodology for comparing the peak capacity of GC x GC to 1D-GC is described. The comparison of the performance of GC x GC to 1D-GC shows that the modulator is the key bottleneck limiting the performance of existing GC x GC. To realize the full potential of GC x GC, duration of injection from a modulator into the second-dimension column should be reduced by an order of magnitude or more. Use of powerful data analysis techniques such as peak deconvolution in both dimensions can further increase resolving power of GC x GC.     

Improved accuracy in the determination of polycyclic aromatic hydrocarbons in air using 24 h sampling on a mixed bed followed by thermal desorption capillary gas chromatography-mass spectrometry

A new sampling method for the determination of polycyclic aromatic hydrocarbons (PAHs) in ambient air is described. The method is based on active sampling on sorption tubes consisting of polydimethylsiloxane (PDMS) foam, PDMS particles and a TENAX TA bed. After sampling, the solutes are quantitatively recovered by thermal desorption and analysed by capillary GC-MS. The new sampling method has been compared to the classical method using high-volume sampling on a glass fiber filter followed by polyurethane foam for 24h sampling of ambient air. Volumes enriched were 144 l on the mixed bed and 1296 m3 with the classical method. The concentrations measured using the new method were significantly higher that the values obtained using the classical method, i.e. a factor 1.2-3 for the high molecular weight PAHs and up to 35 times for naphthalene and 23 times for acenaphthene. The total toxicity equivalence value (TEQ) for PAHs was ca. two times higher compared to the conventional method, illustrating that the concentrations of PAHs in ambient air have been underestimated until now. Some figures of merit (mean value for 17 PAHs) of the method are repeatability 7.4%, detection limit 13 pg/m3, accuracy 105.6% and linearity 0.996. The method also opens interesting perspectives for the determination of other semi-volatile persistent organic pollutants (POPs) in air as illustrated with the analysis of polychlorinated biphenyls (PCBs) at a workplace during removal of transformer oil.     

Sterically-Hindered Molecular p-Dopants Promote Integer Charge Transfer in Organic Semiconductors

Molecular p-dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground-state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p-dopant 2,2′,2′′-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.     

Unusual odd-electron fragments from even-electron protonated prodiginine precursors using positive-ion electrospray tandem mass spectrometry

Reports of anticancer and immunosuppressive properties have spurred recent interest in the bacterially produced prodiginines. We use electrospray tandem mass spectrometry (ES-MS/MS) to investigate prodigiosin, undecylprodiginine, and streptorubin B (butyl-meta-cycloheptylprodiginine) and to explore their fragmentation pathways to explain the unusual methyl radical loss and consecutive fragment ions that dominate low-energy collision-induced dissociation (CID) mass spectra. The competition between the formation of even-electron ions and radical ions is examined in detail. Theoretical calculations are used to optimize the structures and calculate the energies of both reactants and products using the Gaussian 03 program. Results indicate that protonation occurs on the nitrogen atom that initially held no hydrogen, thus allowing formation of a pseudo-seven-membered ring that constitutes the most stable ground state [M + H](+) structure. From this precursor, experimental data show that methyl radical loss has the lowest apparent threshold but, alternatively, even-electron fragment ions can be formed by loss of a methanol molecule. Computational modeling indicates that methyl radical loss is the more endothermic process in this competition, but the lower apparent threshold associated with methyl radical loss points to a lower kinetic barrier. Additionally, this characteristic and unusual loss of methyl radical (in combination with weaker methanol loss) from each prodiginine is useful for performing constant neutral loss scans to quickly and efficiently identify all prodiginines in a complex biological mixture without any clean-up or purification. The feasibility of this approach has been proven through the identification of a new, low-abundance prodigiosin analog arising from Hahella chejuensis.