Sabrina Clavijo

Determination of polycyclic aromatic hydrocarbons using lab on valve dispersive liquid-liquid microextraction coupled to high performance chromatography.

In this work, dispersive liquid-liquid microextraction (DLLME) method was applied for high performance liquid chromatography (HPLC) determination of 15 PAHs in aqueous matrices.The extraction procedure was automated using a system of multisyringe flow injection analysis coupled to HPLC instrument with fluorescence detector. Factors affecting the extraction process, such as type and volume of extraction and dispersive solvent, extraction time and centrifugation step were investigated thoroughly and optimized utilizing factorial design. The best recovery was achieved using 100 µL of trichloroethylene as the extraction solvent and 900 µL of acetonitrile as the dispersive solvent.The results showed that extraction time has no effect on the recovery of PAHs. The enrichment factors of PAHs were in the range of 86-95 with limits of detection of 0.02-0.6 µg L(-1). The linearity was 0.2-600 µg L(-1) for different PAHs. The relative standard deviation (RSD) for intra- and inter-day of extraction of PAHs were in the range of 1.6-4.7 and 2.1-5.3, respectively, for five measurements.The developed method was used to assess the occurrence of 15 PAHs in tap water, rain waters and river surface waters samples.

Zeolitic imidazolate framework dispersions for the fast and highly efficient extraction of organic micropollutants

Development of advanced strategies for the extraction and preconcentration of trace levels of pollutants is essential for the quality control of water resources. A new procedure for the fast and highly efficient extraction of organic micropollutants from water using dispersions of zeolite imidazolate framework-8 (ZIF-8) crystals in a mixture of solvents is reported. The synergistic effect of using ZIF-8 dispersions in mixtures of water miscible and immiscible solvents enhances mass transfer and greatly improves extraction kinetics and capacity in comparison with the use of porous crystals or solvent microextraction separately. The effect of the ZIF-8 crystal size and surface composition has been evaluated using four different ZIF-8 samples spanning the micro- to nanometer range. The relevant parameters involved in the extraction such as the composition of the dispersion medium, the amount of ZIF-8 crystals, the extraction time, or the volume of dispersion required to ensure the maximum extraction efficiency, has also been studied using diethyl phthalate as a model compound. The use of 26 nm ZIF-8 crystals obtained using n-butylamine modulated synthesis has shown very fast extraction kinetics and excellent enrichment factors ranging from 150 to 380 for a mixture of six phthalate esters listed as priority pollutants by the United States EPA, allowing detection limits below the ng L−1 to be reached.

In-syringe magnetic stirring-assisted dispersive liquid-liquid microextraction and silylation prior gas chromatography-mass spectrometry for ultraviolet filters determination in environmental water samples.

A novel online approach involving in-syringe magnetic stirring assisted dispersive liquid-liquid microextraction and derivatization coupled to gas chromatography-mass spectrometry has been developed for the determination of seven UV filters extensively used in cosmetic products in environmental water samples. The effect of parameters such as the type and volume of extraction solvent, dispersive solvent and derivatization agent, pH, ionic strength and stirring time, was studied using multivariate experimental design. Extraction, derivatization and preconcentration were simultaneously performed using acetone as dispersive solvent, N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) as derivatization agent and trichloroethylene as extraction solvent. After stirring during 160s, the sedimented phase was transferred to a rotary micro-volume injection valve (3 μL) and introduced by an air stream into the injector of the GC through a stainless-steel tube used as interface. The detection limits were in the range of 0.023-0.16 μg L(-1) and good linearity was observed up to 500 μg L(-1) of the studied UV filters, with R(2) ranging between 0.9829 and 0.9963. The inter-day precision expressed as relative standard deviation (n=5) varied between 5.5 and 16.8%. Finally, the developed method was satisfactorily applied to assess the occurrence of the studied UV filters in seawater and pool water samples. Some of the studied UV filters were found in these samples and an add-recovery test was also successfully performed with recoveries between 82 and 111%.

In‐syringe‐assisted dispersive liquid–liquid microextraction coupled to gas chromatography with mass spectrometry for the determination of six phthalates in water samples

A fully automated method for the determination of six phthalates in environmental water samples is described. It is based in the novel sample preparation concept of in-syringe dispersive liquid-liquid microextraction, coupled as a front end to GC-MS, enabling the integration of the extraction steps and sample injection in an instrumental setup that is easy to operate. Dispersion was achieved by aspiration of the organic (extractant and disperser) and the aqueous phase into the syringe very rapidly. The denser-than-water organic droplets released in the extraction step, were accumulated at the head of the syringe, where the sedimented fraction was transferred to a rotary micro-volume injection valve where finally was introduced by an air stream into the injector of the GC through a stainless-steel tubing used as interface. Factors affecting the microextraction efficiency were optimized using multivariate optimization. Figures of merit of the proposed method were evaluated under optimal conditions, achieving a detection limit in the range of 0.03-0.10 μg/L, while the RSD% value was below 5% (n = 5). A good linearity (0.9956 ≥ r(2) ≥ 0.9844) and a broad linear working range (0.5-120 μg/L) were obtained. The method exhibited enrichment factors and recoveries, ranging from 14.11-16.39 and 88-102%, respectively.

Online coupling lab on valve-dispersive liquid–liquid microextraction-multisyringe flow injection with gas chromatography-mass spectrometry for the determination of sixteen priority PAHs in water

A novel approach exploiting lab on valve-dispersive liquid–liquid microextraction-multisyringe flow injection analysis (LOV-DLLME-MSFIA) coupled to gas chromatography-mass spectrometry (CG-MS) is presented. The method is based on the aspiration and mixing of the sample and all required reagents in the holding coil of a LOV-MSFIA system and delivering it into a miniaturized LOV platform equipped with a conical tube used as an extraction chamber (EC), where the mixture of extraction solvent and disperser solvent is added at a high flow rate, resulting in the formation of a cloudy state and extraction of analytes of interest. Because the extraction and dispersive solvent mixture used has a density significantly higher than water, the resulting fine droplets in the mixture, which contain the extracted analyte, are self-sedimented in thirty seconds, not requiring centrifugation for separation of the extraction phase. Afterwards, the extracted fraction is aspirated and transferred to a rotary micro-volume injection valve (MIV), where finally it is introduced via an air stream into the injector of the GC, through a silica capillary transfer line with no stationary phase, used as interface. The potential of the devised LOV-DLLME-MSFIA/CG-MS assembly was demonstrated in the determination of polycyclic aromatic hydrocarbons (PAHs) in tap water, rain water, river surface water and raw landfill leachates. Under optimized conditions, good enrichment factors (EFs) (27–38) and acceptable total DLLME yields (80–102%) were obtained. Calibration curves were linear with correlation coefficients higher than 0.996 in the working range level of 0.25–250 μg L−1, and relative standard deviations (RSD%) were lower than 5% (n = 5). Detection limits were within the range of 0.01–0.07 μg L−1.

Development of a MSFIA sample treatment system as front end of GC-MS for atenolol and propranolol determination in human plasma.

An on-line solid-phase extraction (SPE) method coupled to gas chromatography-mass spectrometry (GC-MS) has been developed for the determination of atenolol (ATN) and propranolol (PRO) in human plasma. The hyphenation of SPE with multisyringe flow injection analysis (MSFIA) allows the simultaneous GC-MS determination of ATN and PRO with high selectivity and sensitivity. On-line preconcentration and derivatisation of the analytes were carried out by means of using restricted access materials (RAM) and microwave (MW) assisted derivatisation reactions with N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA)+1% trimethylchlorosilane (TMCS). Multivariate optimization was applied to optimize experimental conditions. The whole procedure comprising sample pretreatment and analyte determination took about 15 min. However, the overlap of the automatic sample treatment with the GC separation increased the frequency to 7 samples h(-1). The validated method was successfully applied to direct ATN and PRO determination in human plasma.

Use of multiresponse statistical techniques to optimize the separation of diosmin, hesperidin, diosmetin and hesperitin in different pharmaceutical preparations by high performance liquid chromatography with UV-DAD

A new method for the separation and determination of four flavonoids: hesperidin (HES), diosmin (DIO), hesperitin (HTIN), and diosmetin (DTIN) in pure form and pharmaceutical formulations has been developed by using high performance liquid chromatography (HPLC) with UV-DAD detection. Multivariate statistics (2k full factorial and Box Behnken Designs) has been used for the multiresponse optimization of the chromatographic separation, which was completed in 22min, and carried out on a symmetry® C18 column (250×3mm; 5µm) as stationary phase. Separation was conducted by gradient elution mode using a mixture of methanol, acetonitrile and water pH: 2.5 (CH3COOH), as mobile phase. Analytes were separated setting the column at 22°C, with a flow rate of 0.58mLmin-1 and detected at 285nm. Under the optimized conditions, the flavonoids showed retention times of: 8.62, 11.53, 18.55 and 19.94min for HES, DIO, HTIN and DTIN, respectively. Limits of detection and quantification were <0.0156µgmL-1 and <0.100µgmL-1, respectively. Linearity was achieved with good correlation coefficients values (r2=0.999; n=5). Intra-day and inter-day precision were found to be less than 3.44% (n=7). Finally, the proposed method was successfully applied to determine the target flavonoids in pharmaceutical preparations with satisfactory recoveries (between 95.2% and 107.9%), demonstrating that should also find application in the quality control, as well as in the pharmacokinetic studies of these drugs.

Simultaneous dispersive liquid-liquid microextraction derivatisation and gas chromatography mass spectrometry analysis of subcritical water extracts of sweet and sour cherry stems

AbstractCherry stems have been used in traditional medicine mostly for the treatment of urinary tract infections. Extraction with subcritical water, according to its selectivity, efficiency and other aspects, differs substantially from conventional extraction techniques. The complexity of plant subcritical water extracts is due to the ability of subcritical water to extract different chemical classes of different physico-chemical properties and polarities in a single run. In this paper, dispersive liquid-liquid microextraction (DLLME) with simultaneous derivatisation was optimised for the analysis of complex subcritical water extracts of cherry stems to allow simple and rapid preparation prior to gas chromatography-mass spectrometry (GC-MS). After defining optimal extracting and dispersive solvents, the optimised method was used for the identification of compounds belonging to different chemical classes in a single analytical run. The developed sample preparation protocol enabled simultaneous extraction and derivatisation, as well as convenient coupling with GC-MS analysis, reducing the analysis time and number of steps. The applied analytical protocol allowed simple and rapid chemical screening of subcritical water extracts and was used for the comparison of subcritical water extracts of sweet and sour cherry stems. Graphical abstractDLLME GC MS analysis of cherry stem extracts obtained by subcritical water