An enantioselective high-performance liquid chromatography-mass spectrometry method to study the fate of quizalofop-P-ethyl in soil and selected agricultural products

In this study, the attention was focused on quizalofop-ethyl, a chiral herbicide whose formulation has recently been marketed as quizalofop-P-ethyl, i.e. the (+)-enantiomer exhibiting herbicidal activity. To verify the real enantiomeric purity of this product as well as to study its environmental fate, the enantioselective separation of the P- and M- enantiomers of quizalofop-ethyl was achieved on Lux Cellulose-2 column (3‑chloro,4-methylphenilcarbamate cellulose) under isocratic conditions in polar organic mode. Once established that the commercial formulation contains ˜ 0.6% (enantiomeric fraction) of M as an impurity, an HPLC-MS/MS method was developed, validated and applied to the analysis of soil, carrots and turnips treated with the herbicide. A simple solid-liquid extraction allowed recoveries greater than 70%; limits of detections of P and M enantiomers were below 5 ng g-1. The analyses of the real samples showed a modification of the enantiomeric fraction of quizalofop-M-ethyl between the commercial formulation (EFM = 0.63 ± 0.03%) and the analysed matrices (EFM = 7.6 ± 0.1% for carrots; EFM = 0% for the other matrices). This outcome highlighted the occurrence of an enantioselective biotic dissipation, responsible for a greater persistency of the distomer in carrots. On the other hand, since screening analyses revealed the occurrence of residues of the metabolite quizalofop-acid with the same EFs as the ester precursor, it was concluded that the hydrolytic conversion was an abiotic process.

Degradation of synthetic fragrances by laccase-mediated system

Laccase mediator systems are important biodegradation agents as the rate of reaction could be enhanced in the presence of redox mediators. In the present study the commercial enzyme laccase from Trametes versicolor and the redox mediator 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) were used for the biotransformation of the synthetic fragrances 1-(1,2,3,4,5,6,7,8-octahydro-2,3,8,8,-tetramethyl-2-naphthyl)ethan-1-one (Iso-E-Super, OTNE), 1,3,4,6,7,8,-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-[g]-2-benzopyran (Galaxolide, HHCB), 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphtalene (Tonalide, AHTN) and the transformation product of HHCB, 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-[g]-2-benzopyran-1-one (Galaxolidone, HHCB-lactone) in water. A particular focus was to assess the effects of the enzyme laccase from Trametes versicolor in the enantioselective degradation of the target compounds, for this reason gas chromatography with an enantioselective column was used as separation technique followed by mass spectrometry detection. In addition, as enantioselective degradation of musk fragrances was observed in wastewater, sewage sludge and fish samples, enantiomeric fractions of selected compounds were studied during composting. In a period of 144h, the target fragrances could be effectively removed by the enzyme laccase with removal percentages greater than 70%, except AHTN with a removal percentage of 42%. However, the degradation process prompted by the enzyme laccase was shown to be non-enantioselective as no significant differences were observer between the enantiomeric fractions calculated at the beginning and at the end of the degradation process. Meanwhile, the composting process was shown to be enantioselective.

Chiral separation of short chain aliphatic hydroxycarboxylic acids on cinchonan carbamate-based weak chiral anion exchangers and zwitterionic chiral ion exchangers

Chiral short chain aliphatic hydrocarboxylic acids (HCAs) are common compounds being part of different biological processes. In order to control and understand these processes is of pivotal importance to determine the identity of the involved enantiomer or their enantiomeric ratio. In this study the capacity of quinine- and quinidine-derived chiral stationary phases to perform the enantioseparation of eight chiral HCAs (tartaric acid, isocitric acid, malic acid, glyceric acid, 2-hydroxyglutaric acid, 2-hydroxybutyric acid, lactic acid and 3-hydroxybutyric acid) was evaluated. MS-compatible conditions consisting of ACN/MeOH mixtures as eluents with formic acid, acetic acid and/or their ammonium salts as additives, temperatures between 10 and 25°C (except for -20°C for 3-hydroxybutyric acid) and a flow rate of 1.00mL/min yielded full baseline resolution for all studied HCAs. Elution order for the HCA enantiomers was determined revealing different behaviors between the studied compounds.

Preparation and evaluation of immobilized 4-methylbenzoylcellulose stationary phases for enantioselective separations

A photochemical method for immobilizing polysaccharide derivatives on silica gel has been developed and applied to 4-methylbenzoyl cellulose (PMBC). The photochemically immobilized materials have been used as chiral stationary phases (CSPs) for the chromatographic separation of the stereoisomers of chiral molecules. Through to the immobilization which makes the chromatographic material insoluble in almost all organic solvents, there no restriction regarding the kind of solvent used in the mobile phase. This feature permits to considerably extend the possibilities to improve the selectivity of the separations and or the solubility of the solute in the mobile phase. The influence of various parameters such as immobilization process, cross-linker type and amount on the chromatographic properties and chiral recognition ability of the resulting CSPs has been investigated using a set of chiral molecules. The impact of the amount of coated polysaccharide material on chiral recognition ability was also examined.