Automated determination of phenylcarbamate herbicides in environmental waters by on-line trace enrichment and reversed-phase liquid chromatography-diode array detection

Mobility and fate of carbetamide in an agricultural soil

The objective of this work is to gain a better understanding of the fate of carbetamide, as a representative herbicide, after its soil application. To reach this goal, batch and column laboratory experiments were performed and a transport model was proposed consistent with these results. Then field-scale experiments were carried out for two years and the results compared with those that would be obtained from the transport model, once the degradation terms were introduced. All this is done for four different scenarios: first, considering that the soil is under its natural condition; second, the soil is amended with organic carbon by the addition of stabilized sewage sludge; third, considering that the percolating aqueous phase contains a significant quantity of surfactant [Linear Alkyl Benzene Sulfonate, (LAS)]; and fourth, the scenario in which the sewage sludge and the surfactant are present simultaneously. The Freundlich model yields a good fit to the data of the sorption isotherms obtained from batch equilibrium experiments, but the isotherms are close to linear. The batch sorption/desorption kinetic data together with the column and field results indicate that the retention kinetics are quite fast and local equilibrium can be assumed for the description of the sorption phenomenon. Results also prove that carbetamide is moderately retained in the original soil with a mean value of the partition coefficient of carbetamide about 0.46 (L kg(-1)). When the soil is amended with sewage sludge, this coefficient is somewhat lower, about 0.40 (L kg(-1)). A further decrease is observed 0.32 L kg(-1)) when the surfactant (LAS) at critical micelle concentration (CMC) is used. The two-region model yields a good reproduction of the results of carbetamide mobility in the soil, both at the laboratory scale and at the field scale.

Determination of caffeine as a tracer of sewage effluent in natural waters by on-line solid-phase extraction and liquid chromatography with diode-array detection

A new liquid chromatographic (LC) method with automated on-line solid phase extraction was developed to determine caffeine at sub-microgram per litre concentrations in waters. The filtered sample was pre-concentrated in a pre-column, which was backwashed with acidic water at pH of 2.70. The concentrated caffeine was separated using a C18 column with a gradient of water-acetonitrile and detected by diode array detection (DAD) at 210 nm. Four different pre-columns: C18, PRP-1, PLRP-s and Env were evaluated for the on-line solid phase extraction of caffeine. The PLRP-s pre-column allowed the enrichment of up to 100 mL of environmental water sample with highest recovery. The procedure was validated by recovery experiments in water spiked at 0.5 1.0 and 4.0 microg/L. Average recoveries were between 92.1 +/- 5.2% and 97.8 +/- 2.6%. Detection limits as low as 0.1 microg/L from 50 ml of sample were achieved. The proposed method has the advantages of higher reliability and sensitivity, simpler sample preparation and shorter analysis time in comparison with off-line solid-phase extraction. The utility of the method was demonstrated at two field sites: Bolivar and Halls Head (Australia). At Bolivar, the treatment process included 6-week lagoon storage which is believed to have attenuated caffeine, and thus limited its use as an environmental tracer of reclaimed water. At the Halls Head site, where the storage period is shorter, caffeine was detected in both the treated sewage effluent and in groundwater near ponds where the reclaimed water is at similar concentrations. These results suggest that the environmental conditions under which caffeine is conservative require better definition.

Solid-phase extraction: method development, sorbents, and coupling with liquid chromatography

The objective of this review is to provide updated information about the most important features of the new solid-phase extraction (SPE) materials, their interaction mode and their potential for modern SPE. First, the recent developments are given in formats, phases, automation, high throughput purpose and set-up of new types of procedures. Emphasis is then placed on the large choice of sorbents for trapping analytes over a wide range of polarities, such as highly cross-linked copolymers, functionalized copolymers, graphitized carbons or some specific n-alkylsilicas. The method development is given which is based on prediction from liquid chromatographic retention data or solvation parameters in order to determine the main parameters of any sequence (type and amount of sorbent, sample volume which can be applied without loss of recovery, composition and volume of the clean-up solution, composition and volume of the desorption solution). Obtaining extracts free from matrix interferences in a few steps--one step when possible--is now included in the development of SPE procedure. New selective phases such as mixed-mode and restricted access matrix sorbents or emerging phases such as immunosorbents or molecularly imprinted polymers are reviewed. Selectivity obtained by combining two sorbents is described with the use of ion-exchange or ion-pair sorbents. Special attention is given to complete automation of the SPE sequence with its on-line coupling with liquid chromatography followed by various detection modes. This represents a fast, modern and reliable approach to trace analysis. Many examples illustrate the various features of modern SPE which are discussed in this review. They have been selected in both biological and environmental areas.