Solution phase complexing of atrazine by fulvic acid: a batch ultrafiltration technique

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The HPLC–microfiltration method previously described for determining atrazine and hydroxyatrazine species in organic soil has been adapted to a mineral soil. The method was able to monitor atrazine concentrations of less than 1.0 × 10−6 M, which is over 40 times lower than the atrazine concentrations measured in the earlier organic soil experiments. During kinetics.experiments, it also monitored four free and sorbed chemical species instead of only one. Measurements were obtained with much better accuracy and productivity than can be obtained by conventional methods. The atrazine sorption capacity of the mineral soil was also measured. The analytical chemical data produced can support heterogeneous chemical kinetics calculations.

Section: Resultsmentioning

confidence: 96%

Atrazine in mineral soil: the analytical chemistry of speciation

Gamble¹,

Ismaily²

1992

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“…According to the rate-law expressions previously developed (eqs . [8]- [13]) the kinetics are intrinsically second order, but should be pseudo-first order under appropriate experimental conditions. Figure 1 shows results of kinetic experiments obtained using the HPLC-microfiltration method (2) for the present case.…”

Section: Resultsmentioning

confidence: 99%

“…It has since been found, however, that generally only about 1 mol % or less of the protonated carboxyl groups act at any instant as sorption sites (7,8). In the present mineral soil study, C, and 0, are therefore defined in terms of experimentally measured apparent sorption capacities.…”

Section: Atrazine Sorption Equilibriummentioning

confidence: 88%

Atrazine in mineral soil: chemical species and catalysed hydrolysis

Gamble¹,

Khan²

1992

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Equilibrium and kinetics parameters have been evaluated at 25.0 °C for the heterogeneous catalysis of atrazine hydrolysis in slurries of a chemically characterized mineral soil. The fraction of acidic sites that accounts for sorption capacity, and the sorption equilibrium function resemble those for humic acid and organic soil. Sorption and desorption half-lives increased with increasing coverage of sorption sites. The sorption half-lives ranged from 3.6 to 735 days. The desorption half-lives ranged from 1 to 11 days. The hydrolysis half-lives ranged from 9.6 to 168 days and are consistent with Brönsted acid catalysis theory. The relationship of independent variables to data scatter has been analyzed. The information obtained should be useful for water and solute transport models.

“…Whether or not unionized carboxyl groups can be detected and measured in the external solution and whether or not carboxylate anions can be detected and measured in the undissolved humic acid are analytical chemistry questions. The sorption of water creates an internal gel solution in the particles of undissolved humic acid, just as it does with other cation exchanges (42,45,54 The subscripts designate the molarities of the carboxyl groups AH, free protons H+, and carboxylate anions A-in the gel solution. Because it is defined for a mixture of carboxyl groups, -KGA is known to be a weighted average equilibrium function (49,(55)(56)(57)(58)(59)(60).…”

Section: Standardization Of the Humic Acidmentioning

confidence: 99%

“…Previous work with atrazine in fulvic acid solutions has demonstrated interactions between atrazine and unionized carboxyl groups and hydrogen ions (42)(43)(44)(45). The atrazine -fulvic acid solution phase work has indicated that unionized carboxyl groups are hydrogen bonding sites.…”

Section: Introductionmentioning

confidence: 99%

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

Gamble¹,

Khan²

1988

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. J. Chem. 66,2605Chem. 66, (1988.The acidic properties of a Chemozemic 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 Bronsted 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 X lo2, CJ = 0.03 X 10' and 8.5 x lo2, a = 2.3 X lo2, for atrazine and hydroxyatrazine, respectively. The rate constant for conversion on catalytic sites ranges from 1.8 X lo-' day-' k 20% to 2.9 X lo-' day-' r 20%, for atrazine coverage of sites from 9.0 ( p,mol/g) to 1.0 ( p,mol/g).