Fractionation of Extracts useful for the Semivolatile Organic Compounds Analysis
| Authors | |
|---|---|
| Year of publication | 2003 |
| Type | Article in Proceedings |
| Conference | SACH Conference. Analytical chemistry of Organic Contaminants in the Environment |
| MU Faculty or unit | |
| Citation | |
| Field | Analytic chemistry |
| Keywords | Fractionation; Semivolatile Organic Compounds |
| Description | Raw organic extracts of enviromnental samples contain different groups of organic compounds. A number of these compounds depend mainly on extraction solvent and on the type of extracted matrixes. Non-polar solvents extract primarily non-polar compounds like aliphatic hydrocarbons, while polar solvents extract polar compounds. Dichloromethane (DCM) is used in environmental analytical chemistry for persistent organic compounds (POPs) extraction. This solvent is used for its excellent extraction efficiency; its low boiling point facilitates reducing of extract volume, which is necessary because concentrations of POPs in environment are too low. On the other hand excellent extraction efficiency of DCM means very ballast compounds in the extracts. Dichloromethane is excellent solvent for polycyclic aromatic hydrocarbons (PAH) and its derivatives extraction from solids. But these samples mostly contain other compounds that are coextracted with analytes. Presence of these co-extracts increases chemical background and finally complicate POPs determination. Some purification and clean-up steps in analysis process are necessary. These steps exploit differences in chemical or physical properties of compounds in extracts. One of the most used clean-up method is acid-base treatment exploiting various acid-base properties. Chromatography, especially liquid chromatography (LC), is other method used for clean-up extracts. Normal phase LC exploit different polarities of compounds. This technique is used in two forms. The first is column chromatography with silica gel or aluminium oxide as a stationary phase. The second variant is solid phase extraction (SPE) with silica gel or modified silica gel. Polar interactions are the main for elution of compounds. For differently polar compound groups elution are used solvents in order with increasing polarity. The first fraction is eluted by alkane i.e. hexane (nC6) or pentane. Then follow out more polar solvents or its mixture and the last is methanol or acetonitrile. This fractionation enables decrease detection limits at level, that is necessary in environmental samples analysis. In this work are shown results of experiments, that were aimed at using of silica gel open column chromatography for clean-up of organic extracts for PAH, hetero-PAH and their derivatives analysis. Organic extracts were obtained by extraction of road side dust using pressurised solvent extraction and evaporated to dryness.. Different organic solvents (n-hexane, cyclohexane and DCM) which extracts are redissolved in were tested. No significance differences were observed when n hexane or cyclohexane was used. All of three fractions (alkanes, PAH and polar derivatives of PAH) were fully separated. When using dichloromethane, alkanes and PAH eluted together and only oxy-PAH were separated from them. Next part of experiments were aimed at separation PAH from their nitrated derivatives (nitro-PAH). Road side dust was spiked by five nitro-PAH and extracted by pressurised solvent extraction. Combinations of solvents for fractionation were tested. |
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