The water-gas shift reaction over CeO/CuO:Operando SSITKA-DRIFTS-mass spectrometry study of low temperature mechanism

An inverse CeO2/CuO catalyst has been investigated by operando steady-state isotopic transient kinetic analysis (SSITKA) in combination with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under 3% CO +3% H2O reactant mixture at 473 K with the aim of determining intermediates involved in the water gas shift reaction at relatively low temperatures. Among the various species detected in the infrared spectra which may be involved in the reaction, i.e. formates, copper carbonyls and carbonates, a particular type of carbonate species is identified as a reaction intermediate on the basis of detailed analysis of the spectra during isotopic exchange in comparison with the change in the corresponding isotopically labelled CO2 product. 

Enrichment and analysis of nonenzymatically glycated peptides: Boronate affinity chromatography coupled with electron-transfer dissociation mass spectrometry

Nonenzymatic glycation of peptides and proteins by D-glucose has important implications in the pathogenesis of diabetes mellitus, particularly in the development of diabetic complications. However, no effective high-throughput methods exist for identifying proteins containing this low-abundance posttranslational modification in bottom-up proteomic studies. In this report, phenylboronate affinity chromatography was used in a two-step enrichment scheme to selectively isolate first glycated proteins and then glycated, tryptic peptides from human serum glycated in vitro. Enriched peptides were subsequently analyzed by alternating electron-transfer dissociation (ETD) and collision induced dissociation ( CID) tandem mass spectrometry. ETD fragmentation mode permitted identification of a significantly higher number of glycated peptides (87.6% of all identified peptides) versus CID mode (17.0% of all identified peptides), when utilizing enrichment on first the protein and then the peptide level. This study illustrates that phenylboronate affinity chromatography coupled with LC-MS/MS and using ETD as the fragmentation mode is an efficient approach for analysis of glycated proteins and may have broad application in studies of diabetes mellitus.

Time of flight mass spectrometry for quantitative data analysis in fast transient studies using a Temporal Analysis of Products (TAP) reactor

A Time of flight (ToF) mass spectrometer suitable in terms of sensitivity, detector response and time resolution, for application in fast transient Temporal Analysis of Products (TAP) kinetic catalyst characterization is reported. Technical difficulties associated with such application as well as the solutions implemented in terms of adaptations of the ToF apparatus are discussed. The performance of the ToF was validated and the full linearity of the specific detector over the full dynamic range was explored in order to ensure its applicability for the TAP application. The reported TAP-ToF setup is the first system that achieves the high level of sensitivity allowing monitoring of the full 0-200 AMU range simultaneously with sub-millisecond time resolution. In this new setup, the high sensitivity allows the use of low intensity pulses ensuring that transport through the reactor occurs in the Knudsen diffusion regime and that the data can, therefore, be fully analysed using the reported theoretical TAP models and data processing.

Human aflatoxin albumin adducts quantitatively compared by ELISA, HPLC with fluorescence detection, and HPLC with isotope dilution mass spectrometry

Essential to the conduct of epidemiologic studies examining aflatoxin exposure and the risk of heptocellular carcinoma, impaired growth, and acute toxicity has been the development of quantitative biomarkers of exposure to aflatoxins, particularly aflatoxin B-1. In this study, identical serum sample sets were analyzed for aflatoxin-albumin adducts by ELISA, high-performance liquid chromatography (HPLC) with fluorescence detection (HPLC-f), and HPLC with isotope dilution mass spectrometry (IDMS). The human samples analyzed were from an acute aflatoxicosis outbreak in Kenya in 2004 (n = 102) and the measured values ranged from 0.018 to 67.0, nondetectable to 13.6, and 0.002 to 17.7 ng/mg albumin for the respective methods. The Deming regression slopes for the HPLC-f and ELISA concentrations as a function of the IDMS concentrations were 0.71 (r(2) = 0.95) and 3.3 (r(2) = 0.96), respectively. When the samples were classified as cases or controls, based on clinical diagnosis, all methods were predictive of outcome (P < 0.01). Further, to evaluate assay precision, duplicate samples were prepared at three levels by dilution of an exposed human sample and were analyzed on three separate days. Excluding one assay value by ELISA and one assay by HPLC-f, the overall relative SD were 8.7%, 10.5%, and 9.4% for IDMS, HPLC-f, and ELISA, respectively. IDMS was the most sensitive technique and HPLC-f was the least sensitive method. Overall, this study shows an excellent correlation between three independent methodologies conducted in different laboratories and supports the validation of these technologies for assessment of human exposure to this environmental toxin and carcinogen.

Determination of geographical origin of distillers dried grains and solubles using isotope ratio mass spectrometry

In recent years distillers dried grains and solubles (DDGS), co-products of the bio-ethanol and beverages industries, have become globally traded commodity for the animal feed sector. As such it is becoming increasingly important to be able to trace the geographical origin of commodities in case of a contamination incident or authenticity issue arise. In this study, 137 DDGS samples from a range of different geographical origins (China, USA, Canada and European Union) were collected and analyzed. Isotope ratio mass spectrometry (IRMS) was used to analyze the DDGS for ²H/¹H, ¹³C/¹²C, ¹⁵N/¹⁴N, ¹⁸O/¹⁶O and ³⁴S/³²S isotope ratios which can vary depending on geographical origin and processing. Univariate and multivariate statistical techniques were employed to investigate the feasibility of using the IRMS data to determine botanical and geographical origin of the DDGS. The results indicated that this commodity could be differentiated according to their place of origin by the analysis of stable isotopes of hydrogen, carbon, nitrogen and oxygen but not with sulfur. By adding data to the models produced in this study, potentially an isotope databank could be set up for traceability procedures for DDGS, similar to the one established already for wine which will help in feed and food security issues arising worldwide.

A further investigation of the kinetic demixing/decomposition of La0.6Sr0.4Co0.2Fe0.8O3- δ oxygen separation membranes

Kinetic demixing and decomposition were studied on three La_0.6Sr_0.4Co_0.2Fe_0.8O_{3- δ} oxygen-separation hollow fibre membrane modules, which were operated under a 0.21/0.009bar oxygen partial pressure difference at 950°C for 1128, 3672 and 5512h, respectively. The post-operation membranes were characterized by Secondary Ion Mass Spectrometry, Scanning Electronic Microscope, Energy Dispersive Spectrum and X-ray Diffraction. The occurrence of kinetic demixing and decomposition was confirmed through the microstructural evolution of the membranes. Secondary-phase grains were found on the air-side surface of the membranes after the long-term operation and Co and Fe enrichment as well as La depletion was found on the surface and in the bulk at the air side. Cation diffusivities were found to be in the order Co>Fe>Sr>La. Kinetic demixing and decomposition rates of the membranes at the air side were found to be self-accelerating with time; the role of A-site deficiency in the perovskite lattice in the bulk near the air side surface is implicated in the mechanism. The oxygen permeability was not affected by the kinetic demixing and decomposition of the material during long-term operation (up to 5512h), however, we may expect permeability to be affected by secondary phase formation on the air-side surface at even longer operational times. © 2010 Elsevier B.V.