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61.
A method for the direct determination of volatile and non-volatile nickel and vanadium compounds in crude oil without previous treatment using direct solid sampling graphite furnace atomic absorption spectrometry is proposed. The crude oil samples were weighed directly onto solid sampling platforms using a microbalance and introduced into a transversely heated solid sampling graphite tube. In previous work of our group losses of volatile nickel and vanadium compounds have been detected, whereas other nickel and vanadium compounds were thermally stable up to 1300 and 1600 °C, respectively. In order to avoid this problem different chemical modifiers (conventional and permanent) have been investigated. With 400 μg of iridium as permanent modifier, the signal started to drop already after two atomization cycles, possibly because of an interaction of nickel (which is a catalyst poison) with iridium. Twenty micrograms of palladium applied in each determination was found to be optimum for both elements. The palladium was deposited on the platform and submitted to a drying step at 150 °C for 75 s. After that the sample was added onto the platform and submitted to the furnace program. The influence of sample mass on the linearity of the response and on potential measurement errors was also investigated using four samples with different nickel content. For the sample with the lowest nickel concentration the relationship between mass and integrated absorbance was found to be non-linear when a high sample mass was introduced. It was suspected that the modifier had not covered the entire platform surface, which resulted in analyte losses. This problem could be avoided by using 40 μL of 0.5 g L−1 Pd with 0.05% Triton X-100. Calibration curves were established with and without modifier, with aqueous standards, oil-in-water emulsions and the certified reference material NIST SRM 1634c (trace metals in residual fuel oil). The sensitivity for aqueous standards and emulsions was close to that for SRM 1634c, making possible the use of aqueous standards for calibration. The limits of detection and quantification obtained for nickel and vanadium under this condition were found to be 0.02 and 0.06 μg g−1, respectively, for both elements, based on 10 mg of sample. Nickel and vanadium were determined in the samples with (total Ni and V) and without the use of Pd (thermally stable compounds), and the concentration of volatile compounds was calculated by difference. The results were compared with those obtained by high-resolution continuum source graphite furnace atomic absorption spectrometry by emulsion technique; no significant differences were found for total Ni and V at the 95% confidence level according to a Student's t-test. 相似文献
62.
The ethanol effect on the Trichoderma reesei cellulases was studied to quantify and clarify this inhibition type. To determine inhibition parameters of crude cellulase
and purified exoglucanase Cel7A, integrated Michaelis-Menten equations were used assuming the presence of two inhibitors:
cellobiose as the reaction product and ethanol as a possible bioproduct of cellulose fermentation.
It was found that hydrolysis of cellulose by crude enzyme follows a model that considers noncompetitive inhibition by ethanol,
whereas Cel7A is very slightly competitively inhibited. Crude cellulase is much more inhibited (K
iul=K
icl=151.9 mM) than exoglucanase Cel7A (K
icl=1.6 × 1015 mM). Also, calculated inhibition constants showed that cellobiose inhibition is more potent than ethanol inhibition both for
the crude enzyme as well as exoglucanase Cel7A. 相似文献
63.
Deuterium labeling in the acetate derivatives of cholic acid demonstrates that electron impact induced consecutive loss of HOAc from the molecular ion occurs in the following order of decreasing preference: 12α-OAc > 7α-OAc > 3α-OAc. Numerous examples are presented showing that consecutive loss of HOAc from a common ion generally increases progressively with relative intensity. In the acetate pregnan-20-one derivatives of cholic acid, loss of 43 mass units from the molecular ion comes from the 12α-OAc and not the 17β-acetyl sidechain. Ketene is ejected from an acetoxy group located in an α position to a carbonyl on which an ion-radical charge is localized. 相似文献
64.
Jerry Ray Dias 《Journal of mathematical chemistry》1990,4(1):17-29
The genesis of the aufbau and excised internal structure concepts is traced. These concepts were pivotal to the first published enumerations of the strictly peri-condensed, non-Kekuléan, and essentially strain-free total resonant sextet benzenoid groups. Aperiodic table set is defined as a partially ordered set forming a two-dimensional array which complies with thetriad principle where a central element has a metric property that is the arithmetic mean of two adjacent surrounding member elements. 相似文献
65.
Jerry Ray Dias 《Journal of mass spectrometry : JMS》1976,11(4):333-346
Mass spectra of various functionalized lanostanes and their deuterated analogs are compared. It is proposed that the transfer of a hydrogen from the 18-methyl group to the 11-oxo group via a McLafferty rearrangement is made geometrically possible by prior ionization of the 13,14 bond which allows an optimum interatomic distance between the oxygen and hydrogen to be acquired; the 8,9 double bond is a requisite for electronic induction of this specific process. Transfer of the hydrogen from the 7β-hydroxy group to position 14 is implicated in the mass spectrum of 3β-acetoxy-7β-hydroxy-5α-lanostan-11-one. 相似文献
66.
67.
Simulation of aerated lagoon using artificial neural networks and multivariate regression techniques
Karla Patricia Oliveira-Esquerre Aline C. da Costa Roy Edward Bruns Milton Mori 《Applied biochemistry and biotechnology》2003,106(1-3):437-449
The aim of this study was to develop an empirical model that provides accurate predictions of the biochemical oxygen demand
of the output stream from the aerated lagoon at International Paper of Brazil, one of the major pulp and paper plants in Brazil.
Predictive models were calculated from functional link neural networks (FLNNs), multiple linear regression, principal components
regression, and partial least-squares regression (PLSR). Improvement in FLNN modeling capability was observed when the data
were preprocessed using the PLSR technique. PLSR also proved to be a powerful linear regression technique for this problem,
which presents operational data limitations. 相似文献
68.
Jerry Ray Dias 《Journal of mathematical chemistry》1990,4(1):127-142
The molecular orbital parameters for tricarbonyl(tetrahapto-unsaturated-hydrocarbon)iron complexes are computed using graph-theoretical methods. The results are in agreement with their experimental properties. 相似文献
69.
Alves Lourdes A. Felipe Maria G. A. Silva JoÃo B. Almeida E. Silva Silvio S. Prata Arnaldo M. R. 《Applied biochemistry and biotechnology》1998,70(1):89-98
Applied Biochemistry and Biotechnology - In order to remove or reduce the concentrations of toxic substances present in the sugarcane bagasse hemicellulose hydrolysate for xyloseto-xylitol... 相似文献
70.