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Journal of Thermal Analysis and Calorimetry
Volume/Issue:
Volume 90: Issue 2
DOI:
https://doi.org/10.1007/s10973-006-7901-y
Authors:
Y. Wan
,
J. Li
, and
D. Chen

Abstact  

The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$Co_3 O_4 + H_2 \to 3CoO + H_2 O, 3CoO + 3H_2 \to 3Co + 3H_2 O$$ \end{document}
which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step, the activation energy, E a, and the pre-exponential factor, A, were found to be 104.35 kJ mol−1 and 1.18�106∼2.45�109 s−1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be f(α)=3/2(1−α)[−ln(1−α)]1/3 or in the integral form: g(α)=[−ln(1−α)]2/3. For the second step, the activation energy, E a, and the pre-exponential factor, A, were found to be 118.20 kJ mol−1 and 1.75�107∼2.45 � 109s−1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1−α)2 or in the integral form: g(α)=[1−α]−1−1.

Restricted access
Acta Chromatographica
Volume/Issue:
Volume 32: Issue 2
DOI:
https://doi.org/10.1556/1326.2019.00654
Authors:
Ahmad Makahleh
,
Kek Wan Cheng
,
Bahruddin Saad
, and
Hassan Y. Aboul-Enein

A hollow-fiber liquid-phase microextraction (HF-LPME), followed by high-performance liquid chromatography–ultraviolet (HPLC–UV) method for the trace determination of carvedilol (β-blocker) in biological fluids, has been described. The separation was achieved using Inertsil ODS-3 C18 (250 mm × 4.6 mm, 3 μm) column with a mobile phase composition of 10 mM phosphate buffer (pH 4.0)–acetonitrile (50:50, v/v) at a flow rate of 1.0 mL/min, under isocratic elution. Several parameters (i.e., type of organic solvent, donor phase pH, concentration of acceptor phase (AP), stirring rate, extraction time, and salt addition) that affect the extraction efficiency were investigated. The optimum HF-LPME conditions were as follows: dihexyl ether as an organic solvent; donor phase pH, 10.7; 0.1 M HCl (AP); 1100-rpm stirring rate; 60-min extraction time; and no salt addition. These parameters have been confirmed using design of experiments. Under these conditions, an enrichment factor of 273-fold was achieved. Good linearity and correlation coefficient were obtained over the range 5–1000 ng/mL (r 2 = 0.9994). Limits of detection and quantitation were 1.2 and 3.7 ng/mL, respectively. The relative standard deviation at 3 different concentration levels (5, 500, and 1000 ng/mL) were less than 13.2%. Recoveries for spiked urine and plasma were in the range 80.7–114%. The proposed method is simple, sensitive, and suitable for the determination of carvedilol in biological fluids.

Open access
Journal of Thermal Analysis and Calorimetry
Volume/Issue:
Volume 94: Issue 3
DOI:
https://doi.org/10.1007/s10973-007-8851-8
Authors:
X. Chen
,
W. Feng
,
W. Miao
,
Y. Yu
,
Y. Shen
,
C. Wan
, and
J. Peng

Abstract  

The power-time curves of Tetrahymena thermophila exposed to tributyltin (TBT) were detected by microcalorimetry. Metabolic rate (r) decreased significantly while peak time (PT) increased with the enhancement of TBT level. Compared with the measured multibiomarker including catalase, lactate dehydrogenase, glutathione S-transferase, ATPase and membrane fluidity, PT and r could be sensitive biomarkers for assessing TBT toxicity at cellular level. The effective concentrations obtained by them were consistent to those obtained by the protozoan community toxicity test. As a result, the microcalorimetric assay of T. thermophila had a great potential in assessing TBT acute toxicity and monitoring TBT pollution in the freshwater ecosystem.

Restricted access