Headspace sorptive extraction using silicone tubes for the determination of chlorobenzenes in water.

A new approach for headspace sorptive extraction is presented and demonstrated for the determination of 12 chlorobenzenes in water samples. It consists of a silicone tube (15-mm length) arranged around a stainless steel rod. This device is fixed on a septum cap and exposed to the headspace of 50 mL of a salt-saturated water sample. After extraction (60-min optimized extraction time), thermodesorption is carried out by direct insertion of the silicone tube into the thermodesorption-gas chromatography-mass spectrometry system. Desorption of the analytes is performed at 250 degrees C for 5 min with a gas flow of 50 mL/min. Repeatability (relative standard deviation 5-10%), extraction yields (9-46%), enrichment factors (129-657), and detection limits (0.002-0.012 microg/L) were determined and four real water samples were analyzed with the headspace tube extraction. The results were verified by standard addition. A comparison of headspace tube extraction with other headspace enrichment techniques underlined the high extraction capacity of the proposed method. A big advantage of tube extraction is the low cost of the silicone material. The tubes can be discarded after single use, avoiding carryover problems and cross-contamination.

Glass-fiber reinforced poly(acrylate)-based sorptive materials for the enrichment of organic micropollutants from aqueous samples.

A novel and simple approach to sorptive materials for the extraction of organic compounds from environmental samples is presented. It entails the use of glass fiber fabric strips coated with a customized poly(acrylate) (PA) formulation as extraction medium. Analytes were enriched by means of shaking of the PA strip in the sample and then subsequently thermally desorbed and analyzed by GC-MS. The performance of the sorptive materials was evaluated by the enrichment of compounds with different polarities (phenols, hexachlorobenzene and hexachlorocyclohexanes) from water samples. Parameters that affect the extraction process such as pH, ionic strength of the solvent, mixing mechanism, extraction time and desorption conditions were investigated. The extraction abilities of the PA extraction medium were compared with that of commercially available poly(dimethylsiloxane) (PDMS) Twisters. The results revealed that the new material shows higher affinity for phenolic compounds presumably due to the presence of polar groups. The partition coefficients for the PA strips estimated in this work were up to 15 times higher than for the PDMS Twister, resulting in higher recoveries and lower detection limits. The method was applied for the quantification of the aforementioned compounds in contaminated surface water samples from Bitterfeld (Germany). Using both PA strips and PDMS Twisters, good agreement of the extraction data was achieved.

Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction as enrichment techniques for the determination of pesticide and benzo[a]pyrene residues in Brazilian sugarcane juice.

The present work compares two modern and environmentally friendly enrichment techniques, stir bar sorptive extraction (SBSE) and membrane-assisted solvent extraction (MASE) for the determination of 18 organic contaminant residues in Brazilian sugarcane juice. Stir bar sorptive extraction and thermal desorption coupled to capillary gas chromatography-mass spectrometry using the selected ion monitoring mode [SBSE-TD-GC-MS(SIM)] and membrane-assisted solvent extraction combined with large volume injection [MASE-LVI-GC-MS(SIM)] methods were assessed taking into account the time of extraction [SBSE (3h) and MASE (30min)], the recoveries [SBSE (0.2-55.3%) and MASE (13.6-103.1%)], the repeatability [SBSE (0.3-19.2%) and MASE (2.6-18.4%)] and the limits of detection [SBSE (0.002-0.71 microgL(-1)) and MASE (0.004-0.56 microgL(-1))] of the selected triazine, organochlorine and organophosphorus pesticides as well as benzo[a]pyrene in sugarcane juice. In general, faster analyses and much better analyte recovery results were achieved with MASE, whereas greater sensitivity and repeatability were obtained with SBSE. SBSE and MASE procedures were applied to the analysis of six sugarcane juice samples from the city São Carlos, in the state of São Paulo, Brazil. A comparison of the results of the pesticide and benzo[a]pyrene residues at microgL(-1) level obtained by the two methods showed good agreement.

Stir bar sorptive extraction and high-performance liquid chromatography-fluorescence detection for the determination of polycyclic aromatic hydrocarbons in Mate teas.

A simple procedure based on stir bar sorptive extraction (SBSE) and high-performance liquid chromatography-fluorescence detection (HPLC-FLD) is presented for the determination of 15 polycyclic aromatic hydrocarbons (PAHs) in herbal tea prepared with Mate leaves (Ilex paraguariensis St. Hil.). The influence of methanol and salt addition to the samples, the extraction time, the desorption time and the number of desorption steps, as well as the matrix effect, were investigated. Once the SBSE method was optimised (10 mL of Mate tea, 2h extraction at room temperature followed by 15 min desorption in 160 microL of an acetonitrile (ACN)-water mixture), analytical parameters such as repeatability (< or = 10.1%), linearity (r2 > or = 0.996), limit of detection (LOD, 0.1-8.9 ng L(-1) ), limit of quantitation (LOQ, 0.3-29.7 ng L(-1) and absolute recovery (24.2-87.0%) were determined. For calibration purposes, a reference sample was firstly obtained by removing the analytes originally present in the lowest contaminated Mate tea studied (via SBSE procedure) and then spiked at 1-1200 ng L(-1)range. The proposed methodology proved to be very convenient and effective, and was successfully applied to the analysis of 11 Mate tea samples commercialised in Brazil. The results of the commercial Mate tea samples found by the SBSE approach were compared with those obtained by liquid-liquid extraction (LLE), showing good agreement.

Continuous monitoring of thermooxidative degradation products of polystyrene by membrane extraction with sorbent interface and gas chromatography.

A novel method for the continuous monitoring of thermooxidative degradation products of polystyrene by membrane extraction with sorbent interface (MESI) and gas chromatography (GC) is developed. The results are compared with solid-phase microextraction-GC, which can extract gases, vapors, and aerosols. The volatile and semivolatile degradation products are identified by mass spectrometry. The membrane used in the MESI-GC analysis shows a high permeation for volatile aromatic hydrocarbons; a low permeation for corresponding volatile aldehydes; and no permeation for less volatile alcohols, acids, and degradation products with a high molecular weight, thus reducing significantly the number of compounds detected from MESI-GC. Sensitivity of the method depends on the time of trapping, which is limited by the breakthrough of the trap. By heating the trap at fixed intervals of time, consecutive gas chromatograms are obtained.