Robert D. Guy

Interactions of some large organic cations with bentonite in dilute aqueous systems

Adsorption studies indicate that paraquat, diquat, and thionine are bound on bentonite by amounts greater than the measured cation-exchange capacity (CEC) of the clay. Methylene blue, new methylene blue, and malachite green are bound by amounts equal to the CEC. The unipositive organocations form aggregates on the clay surface. Aggregation increases with ionic strength and increases the apparent adsorption capacity by 25%. The aggregates are removed by washing with distilled water. Desorption studies show that the dyes are irreversibly bound, whereas the dipositive organocations are reversibly bound. Ionic strength variation reduces adsorption by 15 and 36% in the monovalent and divalent organocation-clay systems, respectively. In the clay-divalent organocation systems adsorption is greater on Na-saturated clay than on K-saturated clay. Adsorption is unchanged over the pH range 4.5–8.5 and decreases steadily below pH 4.0. Changes in adsorption due to changes in temperature are small. The study indicates that ionic strength is the most important variable in clay-organocation interactions.РезюмеИсследования по адсорбции показывают, что паракват, дикват, и тионин связаны в бентоните в количествах больших, чем измеренная катионообменная способность (КОС) глины. Голубой метилен, новый голубой метилен, и зелёный малахит связаны в количествах, соответствующих KОС. Униположительные органокатионы образуют агрегаты на поверхности глины. Агрегация увеличивается с увеличением ионной силы и приводит к увеличению видимой адсорбционной способности до 25%. Агрегаты удаляются при промывке дистиллированной водой. Исследования по десорбции показывают, что красители связаны необратимо, тогда как двухположительные органокатионы связаны обратимо. Изменение ионной силы уменьшает адсорбцию в одновалентных и двухвалентных системах органокатион-глина на 15 и 36% соответственно. В системах глина-двухвалентный органокатион адсорбция значительнее на глине насыщенной натрием, чем на глине насыщенной калием. Адсорбция не изменяется в диапазоне рН 4,5-8,5, и уменьшается равномерно, если рН меньше 4,0. Изменения в адсорбции вследствие изменений температуры малы. Исследования показывают, что ионная сила является наиболее важным фактором в глино-органокатионных взаимодействиях. [Е.С.]ResümeeDie Adsorptionsuntersuchungen deuten darauf hin, daß Paraquat, Diquat, und Thionin an Bentonite in größeren Mengen gebunden sind als die gemessene Kationenaustauschkapazität (CEC) der Tone erlaubt. Methylenblau, Neu-Methylenblau, und Malachitgrün sind in Mengen gebunden, die denen des CEC entsprechen. Die einwertigen organischen Kationen bilden auf der Tonoberfläche Aggregate. Die Aggregatbildung nimmt mit der Ionenstärke zu und vergrößert die scheinbare Adsorptionskapazität um 25%. Die Aggregate werden durch Waschen mit destilliertem Wasser entfernt. Desorptionsuntersuchungen zeigen, daß die Farben irreversibel gebunden sind, während die zweiwertigen organischen Kationen reversibel gebunden sind. Die Variation der Ionenstärke reduzierte die Adsorption um 15 bzw. um 36% in den einwertigen bzw. zweiwertigen organischen Kationen-Ton Systemen. In den Systemen Ton-awei-wertige organische Kationen ist die Adsorption an Na-gesäittigten Ton größer als an K-gesättigten. Die Adsorption bleibt im pH-Bereich von 4,5 bis 8,5 unveräindert und nimmt unter pH 4,0 regelmäßig ab. Änderungen in der Adsorption, die auf Temperaturäinderungen zuräckzufähren sind, sind klein. Die Untersuchnng deutet darauf hin, daß die Ionenstärke die wichtigste Variable bei der Wechselwirkung Ton-organisches Kation ist. [U.W.]RésuméDes études d’adsorption indiquent que le paraquat, diquat, et la thionine sont lié à la bentonite en quantités plus grandes que la capacité d’échange de cations (CEC) mesurée de l’argile. Le bleu de méthylène, le nouveau bleu de méthylètne, et le vert de malachite sont liés en quantités égales à la CEC. Les organocations unipositifs forment des aggrégats sur la surface de l’argile. L’aggrégation croît proportionnellement â la force ionique et accroît la capacité d’adsorption apparente de 25%. Les aggrégats sont retirés par un lavage à l’eau distillée. Des études de désorption montrent que les teintures sont liées irréversiblement, tandis que les organocations dispositifs le sont réversiblement. La variation de force ionique réduit l’adsorption de 15 et 36% dans les systèmes argile-organocations monovalents et divalents, respectivement. Dans les systémes argile-organocations divalents, l’adsorption est plus grande sur l’argile saturtée de Na que sur l’argile saturtée de K. L’adsorption demeure inchangée sur l’étendue de pH 4,5-8,5 et décroît de manière constante sous un pH de 4,0. Les changements d’adsorption dûs à des changements de température soit petits. L’étude indique que la force ionique est la variable la plus importante dans les interactions argile-organocations. [D.J.]

BINDING OF DIQUAT AND PARAQUAT TO HUMIC ACID IN AQUATIC ENVIRONMENTS

Binding of diquat and paraquat to humic acid, at low concentrations of adsorbates and adsorbents, is described under various conditions. Ionic strength and variations in size and charge indicated that binding interaction was mainly electrostatic in nature. Scatchard plots indicated that two binding sites were involved. The stability constants in all cases were of the order of 105 to 104, and the number of binding sites per 100 equivalent weights was in the range of 3 to 23. The nature of the binding sites did not correlate well with the known functional groups on humic acid. Variation in pH suggested that hydrogen ions competed strongly with the herbicides for the binding sites on humic acid. Temperature was shown to exert a small influence on the binding of diquat and paraquat.

Window target-testing factor analysis: theory and application to the chromatographic analysis of complex mixtures with multiwavelength fluorescence detection

Window target-testing factor analysis (WTTFA) is a new data analysis method that can help confirm the presence or absence of an analyte in a severely overlapped chromatogram. It is intended to be used in chromatographic applications with multichannel detection and is based on principal component analysis. The algorithm attempts to determine if the response profile of a target analyte lies within the response subspace of a time window containing unresolved chromatographic peaks. Because the window moves sequentially through the chromatogram, WTTFA allows a relative assessment of match quality. To test the new method, a procedure for simulating complex chromatograms has been developed. The simulated data allow the limitations of WTTFA to be tested under different conditions of chromatographic complexity, spectral overlap, measurement noise, window size and other factors. As a practical demonstration of its utility, the method is applied to the chromatographic analysis of polycyclic aromatic compounds in a complex petroleum distillate using multiwavelength fluorescence detection. WTTFA indicates the presence of 1-methylpyrene in an unresolved cluster of peaks. This is confirmed through a combination of mass spectrometry, heart-cut chromatography and self-modeling curve resolution.

Isolation and characterization of metal-binding proteins (metallothioneins) from lobster digestive gland (Homarus americanus).

Two metallothionein (low-molecular-weight, metal-binding proteins) preparations, MT-1 and MT-2, have been isolated from the digestive gland of American lobster (Homarus americanus) contaminated with Cd. MT-1 contains Cd- and Cu-binding proteins, whereas MT-2 is a reasonably pure Cd-binding protein. The properties of MT-1 and MT-2 with respect to amino acid and elemental compositions, heat stabilities, polarographic, high-performance liquid chromatography (HPLC), and isoelectric focussing behaviors are reported. Lobster metallothioneins share a number of similarities with mammalian metallothioneins with respect to the presence of Cd and Cu, apparent molecular weights, amino acid compositions, UV absorption spectra at various pH, and polarographic behavior, but differ substantially in their electrophoretic behavior.

Interactions of secondary amines with bentonite clay and humic materials in dilute aqueous systems

Abstract The speciation of dimethylamine, diethylamine, dibutylamine, and diethanolamine on bentonite clay saturated with 1) Na and Ca cations, 2) dodecyltrimethylammonium cation, and 3) tannic acid, and on humic acid and peat, has been studied. Adsorption isotherms were determined and the effect of ionic strength and pH on the adsorption were studied. The results show that the amines react with the particulates by ion exchange mechanisms. Hydrogen bonding seems to also contribute to the binding of dibutylamine.

Quadrupolar effects on the retention of aromatic hydrocarbons in normal phase liquid chromatography

SummaryThe retention mechanism of aromatic hydrocarbons in normal phase liquid chromatography has been investigated with respect to the dominant molecular interactions between the polar stationary phase and the solute. The retention behavior of these aromatic solutes is compared with that of aliphatic hydrocarbons with similar molecular polarizability, and the difference between them is interpreted in terms of relative contributions of dispersion, induction and electrostatic interactions to the observed retention. While the aliphatic hydrocarbons are unretained in all of the chromatographic systems studied, the aromatic hydrocarbons show increasing retention with their molecular quadrupole moments. This is consistent with a retention model in which the electrostatic interactions that involve a solute quadrupole moment play a major role in controlling the retention of aromatic hydrocarbons in normal phase liquid chromatography.

The formation of N-nitrosodibutylamine from precursors in model environmental systems

Abstract The formation of N -nitrosodibutylamine from dibutylamine and nitrite in aqueous solutions was studied in the presence of bentonite clay and humic acid. The kinetics, and effects of nitrite and amine concentration, pH, light, and temperature on the nitrosation reaction were evaluated. The N -nitrosodibutylamine yield was enhanced at low pH values, at higher temperatures and in the presence of light. The presence of humic acid was found to enhance the nitrosation while the presence of clay had the opposite effect.

The driving force for solute retention in electron donor-acceptor chromatography: Electrostatic versus charge-transfer interactions

SummaryCharge-transfer interactions are often assumed to be dominant among the noncovalent interactions that govern the solute retention in electron donor-acceptor chromatography. This popular view, however, has been called into question by recent studies that suggest an important role for electrostatic interactions in the formation of donor-acceptor complexes. We reported here an experimental investigation concerning the question as to whether charge-transfer or electrostatic interactions are the driving force for solute retention in donor-acceptor chromatography. Using three chromatographic systems composed of a dinitrobenzene derived stationary phase and a hexane based mobile phase, we determined retention factors for a range of aliphatic and aromatic hydrocarbons and correlated them with molecular properties that describe the solutes dispersion, charge-transfer, and electrostatic characteristics. It was found that the molecular polarizability and ionization potential give either very poor or no correlation with solute retention whereas the molecular quadrupole moment is a linear function of the logarithmic retention factor. These results were interpreted as showing that electrostatic, rather than charge-transfer or dispersion, interactions play a major role in determining solute retention. The dominance of the electrostatic interactions over the other noncovalent interactions was discussed in terms of distance dependency of the interaction energy.

Speciation of bound and free metals evaluated for lobster digestive gland extracts

Abstract A simple method is described for the speciation of metalions in biological extracts with a short desalting gel-filtration column. The system was optimized for the eluent and gel type to provide accurate free metal ion levels and minimum processing times. The four separation media studied were Sephadex G25, Bio-Gel P-6DG, controlled pore glass CPG40, and Fractogel HW40F. The best medium was the Fractogel HW40F because it was not compressible and allowed a pump to be used to obtain uniform flow rates. The eluent was 0.10 M ammonium acetate/0.01 M citric acid adjusted to pH 7.0. This eluent minimized ion/gel interactions and gave a lower salt content relative to other possible eluents. The separation time was 10 min per sample per metal ion of interest. The detection limits relative to the mass of wet tissue for the column/flame spectrometer system were 0.80 μg g−1, 0.80 μg g−1, and 1.6 μg g−1 for zinc, cadmium and copper, respectively. The method is evaluated for a lobster digestive gland extract; the methodology should be applicable to other systems containing nonlabile metal species.

A Model System for the Investigation of Methods of Herbicide Speciation

Organic chemicals in the aquatic environment may exist in a number of chemical forms; for example, the chemical may be in true solution, adsorbed onto inorganic colloids (Haque, 1975), associated with soluble and particulate humic substance (Haque, 1975), dissolved in lipid coatings on particulates (Hartung, 1975; Hance, 1969), and incorporated into the biotic material. The relative distribution of an organic chemical among the different forms will depend on the properties of the compounds (charge, polar functional groups, size etc.), the composition of the particulates, and the ultimate relationship between chemical speciation and bioavailability.