Pervasive autocorrelation of the chemical index of alteration in sedimentary profiles and its palaeoenvironmental implications

The chemical index of alteration has been used widely for reconstruction of the palaeoclimate. However, the mechanisms and environmental factors controlling the chemical index of alteration of sediments are not yet fully understood. In this study, autocorrelations of the chemical index of alteration in nine sedimentary profiles, from both the land and the sea, spanning different geological times, are discussed. The sediments of these profiles have different origins (dust, fluvial or ocean sediments) and are from various climate situations and sedimentary environments. Autocorrelations of chemical index of alteration series are ubiquitously evident in all profiles. It is suggested here that autocorrelations may be caused by post-depositional changes such as persistent weathering and diagenesis. As a result, the chemical index of alteration may not reflect climatic conditions during the time of sediment deposition. This study strongly recommends the confirmation of the reliability and veracity of the chemical index of alteration before it is adopted to evaluate the weathering degree of parent rocks and to reconstruct the past climate. Significant autocorrelations in loess profiles were specifically observed, suggesting that the existing understanding of loess deposition in terms of climate conditions requires re-examination, and that previous reconstructions of rapid climate changes (for example, in centennial-millennial scales) should be treated with caution.

Study of a new derivatizing reagent that improves the analysis of amino acids by HPLC with fluorescence detection: application to hydrolyzed rape bee pollen

A simple and sensitive method for evaluating the chemical compositions of protein amino acids, including cystine (Cys)(2) and tryptophane (Try) has been developed, based on the use of a sensitive labeling reagent 2-(11H-benzo[alpha]-carbazol-11-yl) ethyl chloroformate (BCEC-Cl) along with fluorescence detection. The chromophore of the 1,2-benzo-3,4-dihydrocarbazole-ethyl chloroformate (BCEOC-Cl) molecule was replaced with the 2-(11H-benzo[alpha]-carbazol-11-yl) ethyl functional group, yielding the sensitive fluorescence molecule BCEC-Cl. The new reagent BCEC-Cl could then be substituted for labeling reagents commonly used in amino acid derivatization. The BCEC-amino acid derivatives exhibited very high detection sensitivities, particularly in the cases of (Cys)(2) and Try, which cannot be determined using traditional labeling reagents such as 9-fluorenyl methylchloroformate (FMOC-Cl) and ortho-phthaldialdehyde (OPA). The fluorescence detection intensities for the BCEC derivatives were compared to those obtained when using FMOC-Cl and BCEOC-Cl as labeling reagents. The ratios I (BCEC)/I (BCEOC) = 1.17-3.57, I (BCEC)/I (FMOC) = 1.13-8.21, and UVBCEC/UVBCEOC = 1.67-4.90 (where I is the fluorescence intensity and UV is the ultraviolet absorbance). Derivative separation was optimized on a Hypersil BDS C-18 column. The detection limits calculated from 1.0 pmol injections, at a signal-to-noise ratio of 3, ranged from 7.2 fmol for Try to 8.4 fmol for (Cys)(2). Excellent linear responses were observed, with coefficients of > 0.9994. When coupled with high-performance liquid chromatography, the method established here allowed the development of a highly sensitive and specific method for the quantitative analysis of trace levels of amino acids including (Cys)(2) and Try from bee-collected pollen (bee pollen) samples.

Heat capacity and thermochemical study of trifluoroacetamide (C2H2F3NO)

The low-temperature heat capacities of trifluoroacetamide were precisely determined with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 404 K. A solid-to-solid phase transition, a fusion and a phase transition from a liquid crystalline phase to fully liquid phase have been observed at the temperatures of 336.911+/-0.102, 347.622+/-0.094 and 388.896+/-0.160 K, respectively. The molar enthalpies of these phase transitions as well as the chemical purity of the substance were determined to be 5.576+/-0.004, 11.496+/-0.007, 1.340+/-0.005 kJ mol(-1) and 99.30 mol%, respectively, on the basis of the heat capacity measurements. The molar entropies of the three phase transitions were calculated to be 16.550+/-0.012, 33.071+/-0.029 and 3.447+/-0.027 J mol(-1) K-1, respectively. Further researches of the thermochemical properties for this compound have been carried out by means of TG and DSC techniques. (C) 2000 Elsevier Science B.V. All rights reserved.

Theoretical study of the separation mechanism of ionizable compounds in capillary electrochromatography

The migration mechanism of ionizable compounds in capillary electrochromatography (CEC) is more complicated than in high performance liquid chromatography (HPLC) due to the involvement of electrophoresis and the second chemical equilibrium. The separation mechanism of ionizable compounds in CEC has been studied theoretically. The electrochromatographic capacity factors of ions (k *) in CEC and in the pressurized CEC are derived by phenomenological approach. The influence of pH, voltage, pressure on k* is discussed. in addition, the k * of weak acid and weak base are derived based on acid-base equilibrium and the influence of pH on k * is studied theoretically.

FTIR study of CO and NO adsorbed on nitrided CoMo/Al2O3 catalysts

The states of surface Co and Mo sites on nitrided CoMo supported on Al2O3 were studied by adsorption of CO and NO as IR probe molecules. Three IR bands at 2200, 2060 and 2025 cm(-1) were detected for adsorbed CO. These bands can be respectively attributed to the surface NCO species as a result of CO adsorbed on surface N sites, and linearly adsorbed CO on surface Co and Mo sites in low valence states. The addition of cobalt to the Mo nitride diminishes the band at 2200 cm(-1). This may be due to either the change of the surface structure of the supported nitride, or the formation of a new phase, CoxMoyNz, as suggested in the literature Kim et al., Catal. Lett., 1997, 43, 91 and Logan et al., Catal. Lett., 1998, 56, 165. Comparison of CO and NO adsorption on Mo2N/Al2O3 and CoMoNx/Al2O3 indicates that the presence of cobalt can promote the reduction and nitridation of Mo.

Characterization and thermodynamic study of ultra-fine particle of Ni-B amorphous alloy

Ultra-fine particle of Ni-B amorphous alloy was prepared by chemical reduction of Ni2+ with NaBH4 and characterized with TEM and XRD. The heat capacity and thermal stability were measured with a high-precision automatic adiabatic calorimeter and DTA. The upper limit of applied temperature of the substance was found to be 684 K for use as catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.