Adsorption of Hydrophobic Organic Compounds (HOCs) on Inorganic Surfaces in Aqueous Systems
Yuan Qian, University Duisburg-Essen, Duisburg, Germany
Torsten C. Schmidt, University Duisburg-Essen, Duisburg, Germany

Adsorption of Hydrophobic Organic Compounds (HOCs) on Inorganic Surfaces in Aqueous Systems

Student Presenter

Yuan Qian, Instrumental Analytical Chemistry, University Duisburg-Essen, Lotharstr. 1, Duisburg, D-47048, Germany, Tel: +49 203 379-3575, Fax: +49 203 379-2108, Email: yuan.qian@uni-due.de
Prof. Dr. Torsten C. Schmidt, Instrumental Analytical Chemistry, University Duisburg-Essen, Lotharstr. 1, Duisburg, D-47048, Germany, Tel: +49 203 379-3311, Fax: +49 203 379-2108, Email: torsten.schmidt@uni-due.de

Adsorption of hydrophobic organic compounds (HOCs) to fully submerged inorganic surfaces is an important process both in the environment and in water analysis. Especially for polycyclic aromatic hydrocarbons (PAHs), significant sorption on glass surfaces has been reported in several investigations due to their strong affinity in aqueous solution. This effect can cause the partial loss of analytes and confuse subsequent data interpretation if samples have been stored in glass containers. However, until now, there is no systematic investigation to study sorption of HOCs. Furthermore, in previous investigations, typically conventional batch experiments are utilized. Although this approach is conceptually simple and reliable, it has also some disadvantages: unreliable results due to either weak sorption or very poor solubility, and long equilibration times.  Therefore, a systematic investigation of sorption of HOCs (especially PAHs) from aqueous to mineral phases with a reliable and low time-consuming method is our goal. Based on previous experiences in soil column chromatography, a dynamic approach utilizing HPLC-type columns was utilized in our studies. We characterized the sorption behavior by using both methods.

Sorption is generally quantified by a distribution coefficient (Kd). In typical conventional batch experiments, the distribution coefficient is defined as: the quotient of adsorbed analyte on investigated surface and the equilibrium concentration of analyte in aqueous solution. In column experiments, when the sorption isotherm is linear, the distribution coefficient Kd can be calculated as: Kd = (Rf -1) x θ/ ρb, where Rf is the retardation factor, ρb and θ are the bulk density and porosity of the sorbent, respectively. Retardation factors of the probe compounds relative to a conservative tracer are measured by their retention.

In our investigations, four different inorganic materials (alumina, glass beads, titanium dioxide and silica) have been applied to study sorption of several PAHs (i.e., naphthalene, phenanthrene, anthracene, and pyrene). Linear sorption behavior has been confirmed in our study. Furthermore, the results show that adsorption correlates with the LogKow of PAHs. Finally, temperature and ionic strength effect on Kd  was investigated.

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