Stir octadecyl-modified borosilicate disk for the liquid phase microextraction of triazine herbicides from environmental waters.

In the present article, a novel extraction/stirring approach in the liquid phase microextraction context is presented. The new technique is based on octadecyl coated borosilicate disks which act as support of the organic extracting solvent thanks to hydrophobic interactions. The disk is integrated in a stirring element which favors the transference of the analytes to the extraction phase. The proposed extraction procedure has been characterized using the determination of nine herbicides in water samples by ultra performance liquid chromatography (UPLC) combined with ultraviolet (UV) detection as model analytical problem. All the variables involved in the extraction have been studied and optimized in depth and the optimized technique provides enrichment factors in the range from 79 to 839. The method has been analytically characterized on the basis of its linearity, sensitivity and precision. Limits of detection were in the range from 0.14µg/L (atrazine) to 0.56µg/L (terbumeton) with precision better than 7.3% (expressed as relative standard deviation). Relative recoveries were close to 100%, which demonstrated the applicability of the stir octadecyl-modified borosilicate disk for the proposed analytical problem.

Magnetically confined hydrophobic nanoparticles for the microextraction of endocrine-disrupting phenols from environmental waters.

In this article, a solid-phase extraction approach, which takes advantage of the good extraction capabilities of hydrophobic magnetic nanoparticles (MNPs), is presented. The new approach involves the deposition of a thin layer of MNPs in a dedicated stirring unit based on the dual function of a mini-magnet. The system allows the extraction of the analytes in a simple and efficient way. The approach, which reduces the negative effect of the aggregation tendency of hydrophobic MNPs, is characterized for the resolution of a model analytical problem: the determination of some endocrine-disrupting phenols in water by liquid chromatography-photometric detection. All the variables involved in the extraction process have been clearly identified and optimized. The new extraction mode allows the determination of these compounds with limits of detection in the range from 0.15 µg/L (for 4-tert-octylphenol) to 2.7 µg/L (for 4-tert-butylphenol) with a relative standard deviation lower than 5.3 % (for 4-tert-butylphenol).

Stir frit microextraction: an approach for the determination of volatile compounds in water by headspace-gas chromatography/mass spectrometry.

In this article, a novel extraction approach, called stir frit microextraction (SFME), is presented. The new approach combines the extractive capability of a commercial polyethylene frit (20 µm of pore size) with the stirring in the same device. The proposed extraction procedure allows the determination of benzene, toluene, ethylbenzene, xylene isomers and styrene (BTEX-S) in water samples. The analytes are extracted on the frit, previously conditioned with methanol, under continuous magnetic stirring. Once the extraction is performed, the frit is transferred to a headspace vial where the volatile compounds are desorbed from the frit (90 °C, 30 min) in a headspace module and analyzed by gas chromatography/mass spectrometry. Headspace conditions (time and temperature) as well as extraction conditions (ionic strength, type of stirring, extraction time, stirring rate and sample volume) have been systematically evaluated. The method was characterized on the basis of its linearity, sensitivity and precision. Limits of detection were in the range from 18 ng/L (o-xylene) to 65 ng/L (benzene). The repeatability of the proposed method, expressed as relative standard deviation (RSD) varied between 3.8% (toluene) and 8.2% (m- and p-xylene). The recovery study carried out in different water samples provided an average recovery of 94%, which demonstrated the applicability of the stir frit microextraction for the analytical problem selected in this article.

Determination of non-steroidal anti-inflammatory drugs in urine by the combination of stir membrane liquid-liquid-liquid microextraction and liquid chromatography.

A stir membrane liquid phase microextraction procedure working under the three-phase mode is proposed for the first time for the determination of six anti-inflammatory drugs in human urine. The target compounds are isolated and preconcentrated using a special device that integrates the extractant and the stirring element. An alkaline aqueous solution is used as extractant phase while 1-octanol is selected as supported liquid membrane solvent. After the extraction, all the analytes are determined by liquid chromatography (LC) with ultraviolet detection (UV). The analytical method is optimized considering the main involved variables (e.g., pH of donor and acceptor phases, extraction time, stirring rate) and the results indicate that the determination of anti-inflammatory drugs at therapeutic and toxic levels is completely feasible. The limits of detection are in the range from 12.6 (indomethacin) to 30.7 µg/L (naproxen). The repeatability of the method, expressed as relative standard deviation (RSD, n = 5) varies between 3.4% (flurbiprofen) and 5.7% (ketoprofen), while the enrichment factors are in the range from 35.0 (naproxen) to 72.5 (indomethacin).

Determination of phenols in waters by stir membrane liquid-liquid-liquid microextraction coupled to liquid chromatography with ultraviolet detection.

A simple and rapid method for the determination of eleven phenols in water samples is presented. The target analytes are isolated by stir membrane liquid-liquid microextraction working under the three-phase mode. An alkaline aqueous solution is used as extractant phase while octanol is selected as supported liquid membrane solvent. The target analytes are separated and determined by liquid chromatography (LC) with ultraviolet detection (UV). All the variables involved in the extraction process have been studied in depth. Low detection limits (in the range from 82.1 ng/L for phenol to 452 ng/L for 2,4,5-trichlorophenol) were obtained. The repeatability, expressed as relative standard deviation (RSD), varied between 1.3% (for 4-nitrophenol) and 8.0% (for 4-chlorophenol). The enrichment factors were in the range from 168 (for 2,4,5-trichlorophenol) to 395 (for 3-chlorophenol). The proposed procedure was applied for the direct determination of the eleven phenols in some real water samples including river, well and tap waters. The accuracy was evaluated by means of a recovery study, the results being in the range of 87-120%.

Stir membrane liquid-liquid microextraction.

In this article, a novel liquid phase microextraction technique, called stir membrane liquid-liquid microextraction (SM-LLME), is presented. The new approach combines the advantages of liquid phase microextraction and stirring in the same unit allowing the isolation and preconcentration of the analytes in a simple and efficient way. In the construction of the unit, a polymeric membrane is employed to protect the small volume of the extractant phase. The extraction technique is characterized for the resolution of a model analytical problem: the determination of five selected chlorophenols in water. A two-phase extraction mode is used for the extraction of the analytes with an organic solvent in which an in situ derivatization reaction takes place. The analytes are finally analyzed by gas chromatography/mass spectrometry. All the variables involved in the extraction process have been clearly identified and optimized. The new extraction mode allows the determination of chlorophenols with limits of detection in the range from 14.8 ng/L (for 2,4,5-trichlorophenol) to 22.9 ng/L (for 3-chlorophenol) with a relative standard deviation lower than 8.7% (for 2,6-dichlorophenol).

Sensitive in-surface infrared monitoring coupled to stir membrane extraction for the selective determination of total hydrocarbon index in waters.

In this paper, the direct coupling between stir membrane extraction and infrared spectroscopy working under transmission mode is presented for the sensitive and selective determination of the total hydrocarbon index in waters. For this purpose, a new extraction unit was built using stainless steel in order to maximize the adsorption of the target analytes in the 40-microm-thick polytetrafluoroethylene membrane. The method allows the determination of hydrocarbons in the presence of grease, using hexadecane and stearic acid as model compounds, respectively. The proposal is optimized in depth, taking into account the main experimental variables such as membrane thickness, extraction time, and stirring and sample volume. Later on, the method was characterized on the basis of its linearity, precision, and limits of detection. The combination allows the determination of the hydrocarbon index with a limit of detection of 18 microg L(-1), the precision being (expressed as relative standard deviation) better than 4.3%. The analytical method provides a high sample throughput since some extractions can be performed in parallel, the relative standard deviation between devices being better than 8%. The proposed analytical method is finally compared in terms of analytical figures with counterpart ASTM method, recently presented.

Stir membrane extraction: a useful approach for liquid sample pretreatment.

In this paper, a novel extraction approach based on the use of a polymeric membrane as the extraction medium is described. For this aim, an original unit which allows the magnetic stirring of the membrane during the extraction process has been designed, optimized, and practically evaluated. On one hand, the main variables affecting the extraction process such as the unit design, the stirring rate, the extraction time, the sample volume, and the elution conditions were deeply studied. Once optimized, a model analytical problem, the determination of polycyclic aromatic hydrocarbons in water samples, was selected for practical evaluation of the stir membrane extraction procedure. The method was characterized on the basis of its linearity, precision, and limits of detection. The novel approach was sensitive and precise enough for the detection of the target analytes in the low nanogram per liter range using 25 mL of sample. In fact, limits of detection ranged from 0.8 ng/L (fluoranthene) to 7.6 ng/L (benzo-anthracene) with relative standard deviations lower than 8%.

Dispersive solid phase extraction for in-sorbent surface attenuated total reflection infrared detection.

The combination of dispersive solid phase extraction (DSPE) and attenuated total reflection (ATR) infrared spectroscopy is presented using the joint determination of sorbic and benzoic acids in juice samples as a model analytical problem. The dispersive extraction process allows the selective extraction of the target analytes from the sample matrix allowing their preconcentration prior to their infrared detection. The extraction efficiency is improved compared to the conventional procedures since the interaction between sorbent and analytes is favored with the stirring process. Moreover, the extracted analytes are directly determined in the sorbent. As no elution step is required, analyte dilutions and consumption of organic solvents are avoided. The proposed approach has been qualitative and quantitative studied. The hierarchical cluster analysis permits the sample classification according to the relative concentration of the analytes. The precision of the quantitative analysis was better than 6% with analyte recoveries in the range 87-90%. The proposed method was applied to the analysis of different commercial fruit juice samples. Finally, the main advantages and limitations of the new proposal are presented and compared with existing alternatives.