Capillary gas chromatography of amino acids as their tert-butyldimethylsilyl derivatives in the analysis of serum amino acids in metabolic diseases

Reaction of amino acids with N-methyl-N-(tert-butyldimethylsilyl)trifluoroaceamide (MTbSTFA) in acetonitrile affords good yields of amino acid derivatives with excellent gas chromatographic and mass spectrometric properties. The single-step derivatization procedure is highly reproducible. The TBDMS amino acids are stable at room temperature for at least three days. Only a single peak is observed for each amino acid. The procedure allows simultaneous analysis of asparagine and glutamine together with other serum amino acids. Separation is achieved on a borosilicate glass capillary coated with OV-1. The mass spectra of the TBDMS amino acids possess characteristic diagnostic ions. These properties were used in the sensitive detection by GC-MS and SIM-GC-MS of GABA and pipecolic acid in the serum of a newborn suspected of a Zellweger-type syndrome, which could not be detected by other methods.     

Rare earth elements in sediment profiles from marginal lagoons of the Moji-Guaçu River basin, Brazil

Summary Sediment cores from Catingueiro, Barrinha and Rio das Pedras marginal lagoons of the Moji-Gua?u River basin were analyzed for rare earth elements (REEs), Fe, Ta and Th by instrumental neutron activation analysis (k₀-INAA). Data indicated similarities between Catingueiro and Barrinha lagoons, while a distinct scenario was seen for Rio das Pedras likely due to changes of sedimentation rate in 1950's. By using Fe, Sc, Ta and Th as conservative elements, double normalization technique was performed in order to assess the distribution pattern of Ce, Eu, La, Sm and Tb for each core. In all cases, it was evident a depletion of lighter REE elements in the Rio das Pedras lagoon.     

The mass spectrometric behaviour of benzohydroxaraic and benzothiohydroxamic acids under electron impact

Primary fragmentation reactions in benzohydroxamic and benzothiohydroxamic acids have been studied and compared with those in benzamides and benzothioamides. Mass-analysed ion kinetic energy spectra, collisional activation spectra and spectral data from labelled compounds were used to elucidate fragment ion structures and reaction mechanisms. The mass spectra are shown to be dependent on ion source temperature. Losses of O and H₂O are proved to be thermal in origin. The formation of an S… HO bond, which is analogous to an intramolecular hydrogen bond in solution chemistry, directs many fragmentation pathways. This seems to be the major factor determining the differences between the mass spectra of benzothiohydroxamic acids and those of the corresponding carbonyl compounds.     

Advances in aqueous biphasic systems for biotechnology applications

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