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Properties of surface-modified colloidal particles
- Joan M. Breiner, Michael A. Anderson, Harry W. K. Tom, Robert C. Graham
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- Journal:
- Clays and Clay Minerals / Volume 54 / Issue 1 / February 2006
- Published online by Cambridge University Press:
- 01 January 2024, pp. 12-24
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- Article
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The reactivity of colloidal particles is regulated by their surface properties. These properties affect the wettability, flocculation-dispersion characteristics, ion exchange, sorption capacities and transport of inorganic colloids. Most studies have focused on hydrophilic, charged-particle surfaces, often ignoring the alterations in surface properties produced by the adsorption of natural organic matter, surfactants and other compounds. Adsorption of these substances can potentially render a surface substantially more hydrophobic. Nevertheless, comparatively little is known about changes in surface properties and reactivity of minerals upon sorption of hydrophobic organic compounds. In this study, the properties of four minerals (kaolinite, pyrophyllite, montmorillonite and Min-U-Sil®) and two inorganic materials (X-ray amorphous Al hydroxide and X-ray amorphous Si oxide) were compared before and after treatment with the common silylating agent, trimethylchlorosilane (TMCS). The samples were characterized by measurements of total carbon, cation exchange capacity (CEC), particle size, specific surface area (SSA), electrophoretic mobility, contact angle, particle aggregation, and by X-ray diffraction and diffuse reflectance infrared spectroscopy. For the layer silicates, surface coverage was limited to ∼2% trimethyl silane (TMSi). TMSi covered 7.5% of the Min-U-Sil® surface and 33% of the X-ray amorphous Si oxide. Treatment did not affect the structure of the minerals but reduced the CEC, SSA and electrophoretic mobilities. Water contact angles increased to between 18 and 114° with treatment. While the apolar characteristic of the surfaces decreased minimally with treatment, the Lewis acid/base properties were substantially reduced and interfacial free energy shifted from positive to negative values indicating a more hydrophobic surface character. For all the samples except kaolinite, these changes affected the stability of the colloids in suspension depending upon solution pH. Although the grafting of TMSi altered colloidal mineral surface properties and increased their hydrophobicity, these changes were not sufficient to predict colloid aggregation behavior.
Analysis of Chemical Simulants in Urine: A Useful Tool for Assessing Emergency Decontamination Efficacy in Human Volunteer Studies
- Thomas James, Samuel Collins, Richard Amlôt, Tim Marczylo
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- Journal:
- Prehospital and Disaster Medicine / Volume 35 / Issue 5 / October 2020
- Published online by Cambridge University Press:
- 30 June 2020, pp. 482-487
- Print publication:
- October 2020
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Introduction:
To date, all human studies of mass-casualty decontamination for chemical incidents have relied on the collection and analysis of external samples, including skin and hair, to determine decontamination efficacy. The removal of a simulant contaminant from the surface of the body with the assumption that this translates to reduced systemic exposure and reduced risk of secondary contamination has been the main outcome measure of these studies. Some studies have investigated systemic exposure through urinary levels of simulant metabolites. The data obtained in these studies were confounded by high background concentrations from dietary sources. The unmetabolized simulants have never been analyzed in urine for the purposes of decontamination efficacy assessment.
Study Objective:Urinary simulant analysis could obviate the need to collect skin or hair samples during decontamination trials and provide a better estimate of both decontamination efficacy and systemic exposure. The study objective therefore was to determine whether gross skin contamination as part of a decontamination study would yield urine levels of simulants sufficient to evaluate systemic availability free from dietary confounders.
Methods:In this study, a gas chromatography-tandem mass spectrometry method was developed for the analysis of two chemical simulants, methyl salicylate (MeS) and benzyl salicylate (BeS), in urine. An extraction and sample clean-up method was validated, enabling quantitation of these simulants in urine. The method was then applied to urine collected over a 24-hour period following simulant application to the skin of volunteers.
Results:Both MeS and BeS were present in all urine samples and were significantly increased in all post-application samples. The MeS levels peaked one hour after skin application. The remaining urinary levels were variable, possibly due to additional MeS exposures such as inhalation. In contrast, the urinary excretion pattern for BeS was more typical for urinary excretion curves, increasing clearly above baseline from four hours post-dose and peaking between 12.5 and 21 hours, a pattern consistent with dermal absorption and rapid excretion.
Conclusion:The authors propose BeS is a useful simulant for use in decontamination studies and that its measurement in urine can be used to model systemic exposures following skin application and therefore likely health consequences.