Degradation Study of Mesotrione and Other Triketone Herbicides on Soils and Sediments

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soils, sec 2 • global change, environ risk assess, sustainable land use • research article

Degradation study of mesotrione and other triketone herbicides on soils and sediments

Hanna Barchanska • Aleksandra Kluza • Karolina Krajczewska • Joanna Maj

Received: 17 February 2015 / Accepted: 16 June 2015

Responsible editor: Hailong Wang

H. Barchanska () • A. Kluza • K. Krajczewska • J. Maj

Department of Inorganic, Analytical Chemistryand Electrochemistry, Faculty of Chemistry, Silesian University of Technology, B.Krzywoustego 6 Str, 44-100 Gliwice, Poland

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Analytical performance and extraction procedures

Analytical performance

Chromatography was run using a LiChroCART 125-3 Purospher STAR RP-18e, 5μm column with appropriate precolumn. The injected sample volume was 20 µl. The mobile phase consisted of 0.05% trifluoroacetic acid in water (A) and acetonitrile (B), in the following gradient program: t=0 min: 100%A, flow 0.7 ml/min; t=28 min: 60%A, 40%B, flow 0.7 ml/min; t= 35 min: 30%A, 70%B, flow 1.0 ml/min.

Quantification was performed using the internal standard method. A six point calibration curves prepared in blank matrix extracts were analyzed in triplicate. Linearity was assumed when the regression coefficient was greater than 0.99 with RSD lower than 15%, value established according to the concentration range used in the calibration curve. The instrumental limits of detection (LOD) were calculated by a signal-to-noise ratio of three, using the lowest concentration standard. Limits of quantification (LOQ) were computed as three times of LOD. The analytical wavelengths used for quantitative analysis, and retention times of analytes, and detailed parameters of calibration curves are presented in Table 3.

Extraction procedures

Extraction of triketones and their degradation products from soil and sediment samples was carried out in three stages. The first one (I STAGE) included solid-liquid extraction (SLE). Soil and sediment samples (10g) spiked with standards (5µg/g, prepared according to section 2.2.2 Samples fortification) were mixed with solvent (30 ml) and shaken for 30 min. Methanol, acetonitrile, and the mixture of acetonitrile: methanol (1:1, v/v) were applied, to select the solvent that provided the highest recoveries of all analytes. Next, the extracts were filtered. Since all of them contained matrix compounds, which hindered the chromatographic analysis, therefore, another step of extracts purification was necessary.

According to literature (Barchanska et al. 2012; Chaabane et al., 2005; Chaabane et al., 2008;), liquid-liquid extraction (LEE) is recommended for soil samples to remove the humic acids from the extract (II STAGE). Therefore the extract obtained in the first step was extracted with dichloromethane (2x5 ml). After phase separation, the organic layer was evaporated to dryness, and the residue was dissolved in 0.1 M HCl (5 ml), whereas, the water phase was discarded. To concentrate the extracts and to remove the traces of matrix compounds, the solid-phase extraction (SPE) was applied.

The third step of analytes extraction from soil and sediments was SPE (III STAGE). To establish the SPE conditions providing the separation of analytes and matrix compounds, and at the same time, the highest recovery rates of all analytes,the following sorbents were applied: silica gel modified with octadecyl carbon chains (C18), copolymer styrene-divinylobenzene (SDB) and copolymer N-vinylpyrrolidone-divinylbenzene (HLB). In all cases, the sorbents were conditioned with 3 ml of water and 3 ml of methanol (flow rate 1 ml/min). Next, the extracts obtained in STAGE II were transferred onto sorbents (the flow rate 1 ml/min).

To select a solvent, which provided the highest analytes elution from the sorbents, methanol (5 ml), methanol (2 ml), followed by 4% acetic acid in acetonitrile (3 ml), as well as methanol (2 ml), followed by ethyl acetate (2 ml) and 4% acetic acid in acetonitrile (3 ml) were applied. In all cases the flow rate was 0.5 ml/min. After elution, the solvents were evaporated to dryness and the residue was dissolved in 0.5 ml of methanol before chromatographic analyses. The highest recoveries of all analytes from both soil and sediment samples, as well as sufficient clean-up of the extracts were obtained according to the following procedure:

I STAGE–SLE: acetonitrile;

II STAGE–LLE: dichloromethane;

III STAGE–SPE: sorbent: SDB; elution solvents: ethanol, ethyl acetate and 4% acetic acid in acetonitrile.

The recoveries with SD of all analytes are presented in Table 3.

An exemplary chromatogram of the extract of Soil 2 spiked with standards (5µg/g)is presented in Fig. 1SM.

Fig.1SM Chromatogram of spiked Soil 2 (λ=230 nm)