Small (13)C/(12)C fractionation contrasts with large enantiomer fractionation in aerobic biodegradation of phenoxy acids.

Phenoxy acid herbicides are important groundwater contaminants. Stable isotope analysis and enantiomer analysis are well-recognized approaches for assessing in situ biodegradation in the field. In an aerobic degradation survey with six phenoxyacetic acid and three phenoxypropionic acid-degrading bacteria we measured (a) enantiomer-specific carbon isotope fractionation of MCPP ((R,S)-2-(4-chloro-2-methylphenoxy)-propionic acid), DCPP ((R,S)-2-(2,4-dichlorophenoxy)-propionic acid), and 4-CPP ((R,S)-2-(4-chlorophenoxy)-propionic acid); (b) compound-specific isotope fractionation of MCPA (4-chloro-2-methylphenoxyacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid); and (c) enantiomer fractionation of MCPP, DCPP, and 4-CPP. Insignificant or very slight (ε = -1.3‰ to -2.0‰) carbon isotope fractionation was observed. Equally small values in an RdpA enzyme assay (εea = -1.0 ± 0.1‰) and even smaller fractionation in whole cell experiments of the host organism Sphingobium herbicidovorans MH (εwc = -0.3 ± 0.1‰) suggest that (i) enzyme-associated isotope effects were already small, yet (ii) further masked by active transport through the cell membrane. In contrast, enantiomer fractionation in MCPP, DCPP, and 4-CPP was pronounced, with enantioselectivities (ES) of -0.65 to -0.98 with Sphingomonas sp. PM2, -0.63 to -0.89 with Sphingobium herbicidovorans MH, and 0.74 to 0.97 with Delftia acidovorans MC1. To detect aerobic biodegradation of phenoxypropionic acids in the field, enantiomer fractionation seems, therefore, a stronger indicator than carbon isotope fractionation.

Simultaneous liquid-liquid extraction and dispersive solid-phase extraction as a sample preparation method to determine acidic contaminants in river water by gas chromatography/mass spectrometry.

A sample preparation procedure that combines a liquid-liquid extraction (LLE) with a dispersive solid-phase extraction (DSPE) has been devised to determine residues of four phenoxyacid herbicides, two aminopolycarboxylic acids and five acidic anti-inflammatory drugs in small volumes of river water samples. Two aliquots of acetone (3 and 0.5 mL) were used to extract the analytes from a 10 mL water sample at pH 2 containing 5 mg of octadecylsilane (ODS) sorbent and NaCl at a 5.5 M concentration. Acetone was isolated by the salting-out effect, collected, evaporated and the extract was treated with BF3/methanol to obtain the methyl esters of the analytes and determine them by GC with mass spectrometric detection. Recoveries were comprised between 82% and 114% with relative standard deviations about 5-15% (n=5) within a concentration range about 0.03-44 µg L(-1). The amount of ODS added to sample resulted to be a significant factor in the recovery for most of the analytes as deduced from an experimental design; the sample pH was not a so critical factor. A robustness study of the proposed sample preparation was carried out as defined by Youden and Steiner and an estimation of the uncertainties of the measured concentrations was made following the EURACHEM/CITAC guidelines, too.

Combination of graphene oxide-based solid phase extraction and electro membrane extraction for the preconcentration of chlorophenoxy acid herbicides in environmental samples.

Combination of different extraction methods is an interesting and debatable work in the field of sample preparation. In the current study, for the first time, solid phase extraction combined with electro membrane extraction (SPE-EME) was developed for ultra-preconcentration and determination of chlorophenoxy acid herbicides in environmental samples using capillary electrophoresis (CE). In the mentioned method, first, a 100mL of chlorophenoxy acid herbicides (2-methyl-4-chlorophenoxyacetic acid (MCPA), 2-(2,4-dichlorophenoxy) propanoic acid (2,4-DP) and 2-(4-chloro-2-methylphenoxy) propanoic acid (MCPP)) was passed through a column of graphene oxide as a solid phase, and then the adsorbed herbicides were eluted by 4.0mL of 8% acetic acid (HOAC) in methanol. Then, the elution solvent was evaporated and the herbicides residue was dissolved in 4.0mL of double distilled water (pH 9.0). Afterwards, the herbicides in 4.0mL of the aqueous solution were transferred to an EME glass vial. In the EME step, the herbicides were extracted from the sample solution into the basic acceptor solution (pH 13.0) under electrical potential, which was held inside the lumen of the fiber with 1-octanol as the supported liquid membrane (SLM). Under the optimized conditions, high enrichment factors were obtained in the range of 1950-2000. The limits of quantification (LOQs) and method detection limits (MDLs) were obtained in the range of 1.0-1.5 and 0.3-0.5ngmL(-1), respectively. Finally, the performance of the present method was evaluated for extraction and determination of chlorophenoxy acid herbicides in environmental samples.