Determination of cyclic and linear siloxanes in wastewater samples by ultrasound-assisted dispersive liquid-liquid microextraction followed by gas chromatography-mass spectrometry.

A fast, simple and environmentally friendly ultrasound-assisted dispersive liquid-liquid microextraction (USA-DLLME) procedure has been developed to preconcentrate eight cyclic and linear siloxanes from wastewater samples prior to quantification by gas chromatography-mass spectrometry (GC-MS). A two-stage multivariate optimization approach has been developed employing a Plackett-Burman design for screening and selecting the significant factors involved in the USA-DLLME procedure, which was later optimized by means of a circumscribed central composite design. The optimum conditions were: extractant solvent volume, 13 µL; solvent type, chlorobenzene; sample volume, 13 mL; centrifugation speed, 2300 rpm; centrifugation time, 5 min; and sonication time, 2 min. Under the optimized experimental conditions the method gave levels of repeatability with coefficients of variation between 10 and 24% (n=7). Limits of detection were between 0.002 and 1.4 µg L(-1). Calculated calibration curves gave high levels of linearity with correlation coefficient values between 0.991 and 0.9997. Finally, the proposed method was applied for the analysis of wastewater samples. Relative recovery values ranged between 71 and 116% showing that the matrix had a negligible effect upon extraction. To our knowledge, this is the first time that combines LLME and GC-MS for the analysis of methylsiloxanes in wastewater samples.

Comparison of five integrative samplers in laboratory for the monitoring of indicator and dioxin-like polychlorinated biphenyls in water.

This study aimed at evaluating and comparing five integrative samplers for the monitoring of indicator and dioxin-like polychlorinated biphenyls (PCBs) in water: semi-permeable membrane device (SPMD), silicone rubber, low-density polyethylene (LDPE) strip, Chemcatcher and a continuous-flow integrative sampler (CFIS). These samplers were spiked with performance reference compounds (PRCs) and then simultaneously exposed under constant agitation and temperature in a 200 L stainless steel tank for periods ranging from one day to three months. A constant PCB concentration of about 1 ng·L(-1) was achieved by immersing a large amount of silicone rubber sheets ("dosing sheets") spiked with the target PCBs. The uptake of PCBs in the five samplers showed overall good repeatability and their accumulation was linear with time. The samplers SPMD, silicone rubber and LDPE strip were the most promising in terms of achieving low limits of quantification. Time-weighted average (TWA) concentrations of PCBs in water were estimated from uptake of PCBs using the sampling rates calculated from the release of PRCs. Except for Chemcatcher, a good agreement was found between the different samplers and TWA concentrations ranged between 0.4 and 2.8 times the nominal water concentration. Finally, the influence of calculation methods (sampler-water partition coefficients, selected PRCs, models) on final TWA concentrations was studied.

Constantly stirred sorbent and continuous flow integrative sampler: new integrative samplers for the time weighted average water monitoring.

Two innovative integrative samplers have been developed enabling high sampling rates unaffected by turbulences (thus avoiding the use of performance reference compounds) and with negligible lag time values. The first, called the constantly stirred sorbent (CSS) consists of a rotator head that holds the sorbent. The rotation speed given to the head generates a constant turbulence around the sorbent making it independent of the external hydrodynamics. The second, called the continuous flow integrative sampler (CFIS) consists of a small peristaltic pump which produces a constant flow through a glass cell. The sorbent is located inside this cell. Although different sorbents can be used, poly(dimethylsiloxane) PDMS under the commercial twister format (typically used for stir bar sorptive extraction) was evaluated for the sampling of six polycyclic aromatic hydrocarbons and three organochlorine pesticides. These new devices have many analogies with passive samplers but cannot truly be defined as such since they need a small energy supply of around 0.5 W supplied by a battery. Sampling rates from 181 x 10(-3) to 791 x 10(-3) L/day were obtained with CSS and 18 x 10(-3) to 53 x 10(-3) with CFIS. Limits of detection for these devices are in the range from 0.3 to 544 pg/L with a precision below 20%. An in field evaluation for both devices was carried out for a 5 days sampling period in the outlet of a waste water treatment plant with comparable results to those obtained with a classical sampling method.