scholarly journals DETERMINATION OF RATE CONSTANT AND STABILITY OF ADSORPTION IN COMPETITIVE ADSORPTION OF Cr(III) AND Cd(II) ON HUMIC ACID BY USING THE NEW MODEL OF KINETIC FORMULATION

2010 ◽  
Vol 4 (3) ◽  
pp. 161-167
Author(s):  
Suyanta Suyanta ◽  
Sri Sudiono ◽  
Sri Juari Santosa
Keyword(s):  
Humic Acid ◽  
Rate Constant ◽  
Competitive Adsorption ◽  
Equilibrium Concentration ◽  
Peat Moss ◽  
Water Steam ◽  
Kinetic Formulation ◽  
New Model ◽  
First Order

Determination of rate and stability constants of adsorption in competitive adsorption of Cr(III) and Cd(II) on humic acid by using the new model of kinetic formulation has been done. The new model based on assumption that those adsorption was first order adsorption rearched equilibrium. Humic acid was isolated from Peat moss of Silaut- West Sumatra by modificated Schnitzer method. Humic acid characterization was conducted by using infrared spectrophotometer with KBR pellet method. The experiment of kinetic adsorption was conducted in batch system reactor using erlenmeyer at 25 ± 0.01 oC of water steam bath and in a series of sampling procedure. Initial concentration of both Cr(III) and Cd(II) was 4x10-4 M. Thirty milligrams of humic acid was added to 200 mL of metal solution, and then stirred continuously. At the fixed periode of time, 10 mL of sample was taken using a syringe, then filterd with 0.45 µm filter paper. Concentration of Cr(III) and Cd(II) in the filtrate was determinated by AAS, while that was adsorbed by humic acid was equal to difference between initial and equilibrium concentration. It was concluded that competitive adsorption of Cr(III) and Cd(II) on humic acid was first order adsorption rearched equilibrium as proposed in this research. Adsorption rate constant of Cr(III) on humic acid  at competitive condition was greater than of Cd(II), but on the contrary for stability constant (K). Competition between Cr(III) and Cd(II) to interact with the active side of humic acid was dominated by Cr(III).   Keywords: rate constant, stability and competitive adsorption

Vulcameter Determination of Best Cure

1965 ◽  
Vol 38 (4) ◽  
pp. 757-768 ◽  
Author(s):  
S. D. Gehman ◽  
F. S. Maxey ◽  
S. R. Ogilby
Keyword(s):  
Rate Constant ◽  
Work Load ◽  
Service Performance ◽  
Stress Strain ◽  
First Order ◽  
Testing Laboratories ◽  
Physical Testing ◽  
Strain Testing ◽  
Minimum Number

Abstract Using a continuous cure curve to select a minimum number of stepped cures, it should be possible to vulcanize and test fewer sheets to determine best cure. This procedure is attractive for its potential of expediting the output of physical testing laboratories and especially for reducing the work load of stress-strain testing. Cure curves recorded with the Vulcameter approximated first-order reactions. Equations were derived to calculate the final force and rate constant from recorded force values without carrying the reaction to completion. A chart is suggested to assist in calculating the rate constant. Time for a given fractional rise in force depends only on the rate constant so that a chart for obtaining it is relatively simple. Experience and correlation with service performance in selecting best cures is emphasized. 95% rise times from Vulcameter curves were compared with conventionally selected best cures for a wide variety of compounds. Indications are that experience with the method might reduce the number of test-sheet cures to determine optimum stress-strain properties to one, two, or three depending upon the compound and the exactness required.

Atrazine hydrolysis in aqueous suspensions of humic acid at 25.0 °C

1988 ◽  
Vol 66 (10) ◽  
pp. 2605-2617 ◽  
Author(s):  
Donald S. Gamble ◽  
Shahamat U. Khan
Keyword(s):  
Humic Acid ◽  
Rate Constant ◽  
Free Acid ◽  
Equilibrium Constants ◽  
Environmental Research ◽  
Separate Determination ◽  
Sorption Equilibrium ◽  
Catalytic Sites ◽  
Free Acid Form

The acidic properties of a Chernozemic humic acid were determined by equilibrium titration. The number of carboxyl groups is 2.828 (mmol/g) ± 0.5%. The results were used for an investigation of Brönsted acid catalysis of atrazine hydrolysis by a suspension of the humic acid. There is sufficient sorption so that the rates of change of atrazine and product hydroxyatrazine in solution differ both from each other and form the rate of atrazine conversion on the catalytic sites. An important objective of this work was the separate determination of the sorption equilibrium constants for atrazine and hydroxyatrazine, and the rate constant for atrazine conversion on the catalytic sites. All three constants are relevant to environmental research. The apparent rate constants for changes in solution are experimental artifacts however, not useful for such research. Calculated in terms of carboxyl sorption sites in the free acid form, the sorption equilibrium constants were 1.74 × 102, σ = 0.03 × 102 and 8.5 × 102, σ = 2.3 × 102, for atrazine and hydroxyatrazine, respectively. The rate constant for conversion on catalytic sites ranges from 1.8 × 10−1day−1 ± 20% to 2.9 × 10−1day−1 ± 20%, for atrazine coverage of sites from 9.0(μmol/g) to 1.0(μmol/g).

scholarly journals The determination of specificity constants in enzyme-catalysed reactions

1986 ◽  
Vol 239 (1) ◽  
pp. 221-224 ◽  
Author(s):  
I E Crompton ◽  
S G Waley
Keyword(s):  
Rate Constant ◽  
Competitive Inhibition ◽  
Order Rate Constant ◽  
Beta Lactamase ◽  
Initial Concentration ◽  
First Order ◽  
Order Rate ◽  
Accurate Procedure ◽  
Hydrolysis Of

A convenient and accurate procedure for determining the kinetic parameter Vmax./Km is described. This avoids the error in the usual method of taking the observed first-order rate constant of an enzymic reaction at low substrate concentration as Vmax./Km. A series of reactions is used in which the initial concentration of substrate is below Km (e.g. from 5% to 50% of Km). Measurements are taken over the same extent of reaction (e.g. 70%) for each member of the series, and treated as if the kinetics were truly first-order. The reciprocal of the observed first-order rate constant is then plotted against the initial concentration of substrate: the reciprocal of the ordinate intercept is Vmax./Km. The procedure, as well as being applicable to simple reactions, is shown to be valid when there is competitive inhibition by the product, or when the reaction is reversible, or when there is competitive or mixed inhibition. The hydrolysis of cephalosporin C by a beta-lactamase from Pseudomonas aeruginosa is used to illustrate the method.

A Kinetic Determination of the Dissociation Energy of the C—O Bond in Anisole

1975 ◽  
Vol 53 (22) ◽  
pp. 3330-3338 ◽  
Author(s):  
S. Paul ◽  
M. H. Back
Keyword(s):  
Rate Constant ◽  
Dissociation Energy ◽  
Stabilization Energy ◽  
Phenoxy Radical ◽  
Methyl Radicals ◽  
Kinetic Determination ◽  
First Order

The rate of dissociation of anisole into phenoxy and methyl radicals has been measured using a toluene scavenging technique. The rate was measured by the production of methane over the range of temperature 720−795 K and was shown to be first order in anisole concentration and homogeneous. The rate constant, expressed in the Arrhenius form, was[Formula: see text]The dissociation energy, D298(C6H5O—CH3), therefore equals 57 ± 2 kcal/mol, giving ΔHf(C6H5O) = 5 kcal/mol. The stabilization energy of the phenoxy radical is discussed.

Improvement of a direct spectrophotometric assay for routine determination of superoxide dismutase activity

1991 ◽  
Vol 37 (11) ◽  
pp. 1993-1999 ◽  
Author(s):  
B J Bolann ◽  
R J Ulvik
Keyword(s):  
Superoxide Dismutase ◽  
Rate Constant ◽  
Spectrophotometric Method ◽  
Order Rate Constant ◽  
Spectrophotometric Assay ◽  
Alkaline Ph ◽  
First Order ◽  
Pseudo First Order ◽  
Superoxide Dismutase Mimics

Abstract The growing interest in measuring superoxide dismutase (EC 1.15.1.1) in many diseases calls for useful routine assays. For this purpose, the direct spectrophotometric method of Marklund (J Biol Chem 1976;251:7504-7) was improved to offer an alternative to the imprecise, indirect assays currently used. The decay of O2.- (from KO2) at pH 9.5 was monitored as the decrease in delta A (delta A = A250nm-A360nm). Superoxide dismutase was determined from the pseudo-first-order rate constant of O2.- dismutation. The precision of the assay was improved by increasing the concentration of O2.- and expanding the interval for measurements of O2.- concentrations to 4-16 mumol/L. Other assay characteristics, including temperature, were also optimized. In hemolysate the assay had a within-day CV of 5.5-13% and a between-day CV of 4%. Mn-superoxide dismutase and some superoxide dismutase mimics are inhibited at alkaline pH. Therefore, the method is primarily recommended for Cu,Zn-superoxide dismutase.

Sign in / Sign up

Export Citation Format

Share Document