Naslov
Comparison of sample preparation methods in the determination of environmental pollutant sorption on solid sorbents

Autori
Prosen, Helena ; Fingler, Sanja ; Drevenkar, Vlasta ; Zupančič-Kralj, Lucija ; Pižorn, Barbara ; Kadunc, Peter

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
12th International Symposium on Separation Sciences, Lipica 2006, Book of Abstracts / Strlič, Matija ; Buchberger, Wolfgang - Ljubljana : Slovensko kemijsko društvo, 2006, 145-147

Skup
12th International Symposium on Separation Sciences

Mjesto i datum
Lipica, Slovenija, 27.09.2006. - 29.09.2006

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
solid-phase extraction; solid-phase microextraction; organochlorine pesticides; PCB; triazine pesticides; adsorption isotherms

Sažetak
After their introduction in the environment, various environmental pollutants undergo a number of different processes. One of the most important is the sorption to the soil, depending both on the soil and pollutant properties. The extent of pollutant binding to the soil or any other solid sorbent is commonly expressed as a distribution coefficient Kd between solid and aqueous phase: Kd = q/Cw, where q (or Cs) is the equilibrium mass of compound sorbed per unit mass of sorbent in mg/kg, and Cw is the equilibrium mass concentration of compound in the solution in mg/L [1]. The above equation is valid only if the adsorption isotherm for the pollutant on the sorbent is linear. If this is not the case, a more general Freundlich equation should be applied: q = Kf Cw^n or, in logarithmic form:log q = log Kf + n log Cw, where q and Cw are the same as above, Kf is the Freundlich sorption coefficient and n is the Freundlich exponent [1-3]. In principle, Kd is not equal to Kf except if n=1, but is usually calculated from Kf by different approaches, e.g. by calculating Kd at a mean value Cw in the concentration range employed in the experiment [2] or by calculating Kd at Cw>Kf [3]. Experimental data for adsorption isotherm construction are usually obtained by batch equilibrium method. The procedure is relatively simple, but there are many experimental variables that may influence the process and lead to mistakes in the evaluation of the extent of the sorption. Concentration of the pollutant after the equilibrium is reached is usually measured in the solution (Cw) by a number of different analytical methods: UV spectroscopy, HPLC, GC, fluorescence quenching method (fluorescent compounds), radioactivity measurement (radiolabelled compounds). Extraction methods used prior to analysis are usually exhaustive: liquid-liquid extraction - LLE [1, 4], solid-phase extraction [5]. Recently, solid-phase microextraction - SPME has been introduced in the field of free concentration measurements [4, 6, 7]. As the amounts extracted by SPME are usually below 10% or even below 1%, the depletion of the compound from the solution might be considered negligible [8]. Distribution coefficients Kd obtained by SPME-GC determination of equilibrium concentrations after the sorption experiment have been reported to be significantly different for some compounds compared to those obtained by other determination methods [7]. In the present work, we have compared two sample preparation methods (SPE, SPME) for the extraction of target compounds (organochlorine pesticides and their degradation products, PCBs, triazine pesticides) from the aqueous phase after the sorption on solid sorbent. Parameters of batch equilibrium method and gas chromatographic method for the final analysis were kept constant after the determination of optimal conditions. Various parameters influencing the SPE and SPME were optimized and evaluated. Finally, the adsorption isotherm parameters obtained by both methods were compared. For solid-phase extraction (SPE), the conditions that were varied were: use of extraction cartridges or extraction disks, volume of extracted aqueous phase, effect of neutral salt addition and pH of the solution, elution solvent and its volume, effect of previous filtration of the aqueous phase. Especially the latter has had a considerable effect on the amount of the pollutants remaining in the solution, which puts the filtration as a means of separating the solid from the liquid phase after the sorption experiment in a somewhat questionable light. For solid-phase microextraction (SPME), extraction time, volume of the aqueous phase and effect of dissolved organic matter - DOM (commercially available humic acid) were evaluated. The latter experiment has confirmed that some of the target compounds strongly partition into the DOM and that with SPME, only the free fraction of compounds is actually sampled [10]. In the gas chromatographic method, either electron capture detector for chlorinated compounds or thermionic detector for triazines were used. For the batch equilibrium sorption experiments, the optimal ratio of solid sorbent to the aqueous phase and the appropriate sorption time were determined. Sorption of the target compounds to the glass walls of the vessels was evaluated separately and accounted for in the calculation of adsorption isotherm parameters. Sorption experiments were conducted using two different sorbents: forest soil (total organic carbon content 4.7%) and Florisil as a model sorbent for silicates. The majority of the adsorption isotherms were non-linear and the calculated logKf and n for the same compound on the same sorbent were in most cases different for both sample preparation methods. In general, the logKf obtained by aqueous concentration measurements by SPME-GC were higher, pointing to the fact that by SPME, the true aqueous concentration of the compounds is actually obtained, while by SPE the compounds partitioned into DOM or sorbed on non-settling particulate matter in the solution are also extracted. [1] Kleineidam S, Schueth Ch, Grathwohl P, Environ. Sci. Technol. 36 (2002) 4689-4697. [2] Socias-Viciana MM, Hermosin MC, Cornejo J, Chemosphere 37 (1998) 289-300. [3] Arienzo M, Crisanto T, Sanchez-Martin MJ, Sanchez-Camazano M, J. Agric. Food Chem. 42 (1994) 1803-1808. [4] Poerschmann J, Zhang Zh, Kopinke FD, Pawliszyn J, Anal. Chem. 69 (1997) 597-600. [5] Konda LN, Czinkota I, Fueleky G, Morovjan G, J. Agric. Food Chem. 50 (2002) 7326-7331. [6] Zambonin CG, Catucci F, Palmisano F, Analyst 123 (1998) 2825-2828. [7] Lee S, Gan J, Liu WP, Anderson MA, Environ. Sci. Technol. 37 (2003) 5597-5602. [8] Heringa MB, Hermens JLM, TrAC 22 (2003) 575-587. [9] Prosen H, Fingler S, Zupančič-Kralj L, Drevenkar V, submitted for publication in Chemosphere.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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