Microwave-assisted extraction and mild saponification for determination of organochlorine pesticides in oyster samples

A sample-preparation procedure (extraction and saponification) using microwave energy is proposed for determination of organochlorine pesticides in oyster samples. A Plackett-Burman factorial design has been used to optimize the microwave-assisted extraction and mild saponification on a freeze dried sample spiked with a mixture of aldrin, endrin, dieldrin, heptachlor, heptachorepoxide, isodrin, transnonachlor, p, p'-DDE, and p, p'-DDD. Six variables: solvent volume, extraction time, extraction temperature, amount of acetone (%) in the extractant solvent, amount of sample, and volume of NaOH solution were considered in the optimization process. The results show that the amount of sample is statistically significant for dieldrin, aldrin, p, p'-DDE, heptachlor, and transnonachlor and solvent volume for dieldrin, aldrin, and p, p'-DDE. The volume of NaOH solution is statistically significant for aldrin and p, p'-DDE only. Extraction temperature and extraction time seem to be the main factors determining the efficiency of extraction process for isodrin and p, p'-DDE, respectively. The optimized procedure was compared with conventional Soxhlet extraction.     

Styrene Emulsion Polymerization above the CMC: New Evidence on Particle Nucleation by means of AFFFF

Summary: The number (N) and size distribution of particles (PSD) of a styrene emulsion polymerization above the CMC were studied by means of asymmetric flow‐field flow fractionation (AF⁴). Bimodal PSDs were obtained, suggesting that coagulation of the primary particles is not as extensive as would be expected, according to the coagulative mechanism. AF⁴ allowed it to be demonstrated that N is constant during interval II, and that the resolution limit of other particle sizing techniques can lead to erroneous mechanistic inferences, from the evolution of N.

Particle size distribution measured at low conversion for the emulsion polymerization of styrene, obtained by AF⁴ and DLS. The initial surfactant (S₀), initiator (I₀) and monomer (M₀) concentrations are indicated in the figure.     

Methylmercury determination in biological samples by derivatization,solid-phase microextraction and gas chromatography with microwave-induced plasma atomic emission spectrometry

A method for the extraction and gas chromatographic determination of methylmercury in biological matrices is presented. By combining the advantages of two extraction techniques-microwave-assisted extraction (MAE) and solid-phase microextraction (SPME)--the separation of methylmercury from biological samples is possible. Specifically, the procedure involves microwave extraction with 3 M hydrochloric acid, followed by aqueous-phase derivatization with sodium tetraphenylborate and headspace SPME with a silica fibre coated with polydimethylsiloxane (PDMS). For optimization of the derivatization-SPME procedure, a central composite experimental design with alpha = 1.682 and two central points was used to model gas-chromatographic peak areas as functions of pH, extraction temperature and sorption time. A desirability function was then used for the simultaneous optimization for methylmercury and Hg(II). The optimal derivatization-SPME conditions identified were close to pH 5, temperature 100 degrees C, and sorption time 15 min. The identification and quantification of the extracted methylmercury is carried out by gas chromatography with microwave-induced plasma atomic emission spectrometry detection. The validity of the new procedure is shown by the results of analyses of certified reference materials.     

Design of a field flow preconcentration system for cadmium determination in seawater by flow-injection-atomic absorption spectrometry

A field flow preconcentration system (FFPS) for cadmium determination in seawater is described. Seawater samples are collected and preconcentrated in situ by passing them with a peristaltic pump through a minicolumn packed with Amberlite XAD-4 impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. Thus, cadmium is complexed, retained, and preconcentrated without the interference of the saline matrix. Minicolumns loaded with cadmium are then returned to the laboratory where they are incorporated into a flow injection system and eluted with a small volume of an ethanolic solution of hydrochloric acid into the nebuliser-burner system of a flame atomic absorption spectrometer. The optimization of FFPS design is presented, and the stability and characteristics of the Cd-loaded minicolumns are studied in detail. The detection limit for Cd in seawater based on an enrichment factor of 1059 was 3.8 ng l(-1). The precision (R.S.D.) obtained for different amounts of cadmium was in the range 4.1-6.5% at the 25-100 ng l(-1) level. Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater samples from Galicia (Spain).     

Solid-phase microextraction with on-fiber derivatization for the analysis of anti-inflammatory drugs in water samples

A sensitive and solvent-free procedure for the determination of non-steroidal acidic anti-inflammatory drugs in water samples was optimized using solid-phase microextraction (SPME) followed by on-fiber silylation of the acidic compounds and gas chromatography-mass spectrometry (GC-MS) determination. Microextraction was carried out directly over the filtered water samples using a polyacrylate fiber. Derivatization was performed placing the SPME fiber, loaded with the extracted analytes, in the headspace of a vial containing 50 microl of N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Derivatives were desorbed for 3 min in the GC injector. Influence of several parameters in the efficiency of microextraction (volume of sample, time, pH, type of fiber coating, etc.) and derivatization steps (time, temperature and volume of MTBSTFA) was systematically investigated. In the optimal conditions an excellent linearity over three orders of magnitude and quantification limits at the ng/l level (from 12 to 40 ng/l) were achieved. The proposed method was applied to the determination of acidic compounds in sewage water and results compared to those obtained using solid-phase extraction (SPE) followed by the derivatization of the compounds in the organic extract of the solid-phase extraction cartridge.     

The p75 neurotrophin receptor localization in blood-CSF barrier: expression in choroid plexus epithelium

Background  

The presence of neurotrophins and their receptors Trk family has been reported in the choroid plexus. High levels of Nerve Growth Factor (NGF), Neurotrophin-4 (NT-4) and TrkB receptor were detected, while nothing was know about p75 neurotrophin receptor (p75NTR) in the choroid plexus epithelial cells. In neurons, p75NTR receptor has a dual function: promoting survival together with TrkA in response to NGF, and inducing apoptotic signaling through p75NTR. We postulated that p75NTR may also affect the survival pathways in the choroid plexus and also undergoes regulated proteolysis with metalloproteases.     

Screening of Contaminants of Emerging Concern in Surface Water and Wastewater Effluents,Assisted by the Persistency-Mobility-Toxicity Criteria

Contaminants of emerging concern (CECs) are compounds of diverse origins that have not been deeply studied in the past which are now accruing growing environmental interest. The NOR-Water project aimed to identify the main CECs and their sources in the water environment of Northern Portugal–Galicia (located in northwest Spain) transnational region. To achieve these goals, a suspect screening analytical methodology based on the use of liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) was applied to 29 sampling sites in two campaigns. These sampling sites included river and sea water, as well as treated wastewater. The screening was driven by a library of over 3500 compounds, which included 604 compounds prioritized from different relevant lists on the basis of the persistency, mobility, and toxicity criteria. Thus, a total of 343 chemicals could be tentatively identified in the analyzed samples. This list of 343 identified chemicals was submitted to the classification workflow used for prioritization and resulted in 153 chemicals tentatively classified as persistent, mobile, and toxic (PMT) and 23 as very persistent and very mobile (vMvP), pinpointing the relevance of these types of chemicals in the aqueous environment. Pharmaceuticals, such as the antidepressant venlafaxine or the antipsychotic sulpiride, and industrial chemicals, especially high production volume chemicals (HPVC) such as ε-caprolactam, were the groups of compounds that were detected at the highest frequencies.     

Determination of natural and synthetic estrogens in water by gas chromatography with mass spectrometric detection

A procedure for the determination of six natural and synthetic estrogens (diethylstilbestrol, estrone, 17beta-estradiol, mestranol, 17alpha-ethinylestradiol and estriol) in water samples is described. Samples, up to 2000 ml, were concentrated using Oasis HLB solid-phase extraction cartridges. Analytes were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide and determined by GC-MS or GC-MS-MS. The reactivity of several silylation reagents versus aliphatic and aromatic hydroxyl groups contained in the structure of the selected analytes was evaluated. Influence of parameters such as sample pH, nature of the water samples and derivatization conditions on the performance of the whole analytical procedure was systematically studied. Under optimal conditions, quantification limits between 1 and 3 ng/l were achieved for the determination of the considered estrogens in sewage water.     

Determination of trace levels of aquaculture chemotherapeutants in seawater samples by SPME-GC-MS/MS

A sensitive and efficient solid-phase microextraction (SPME) method for the determination of organophosphorous (OPPs) and pyrethroid pesticides (Pyrs) in aquaculture-seawater samples by using GC with MS/MS (GC-MS/MS) was developed. Dichlorvos and chlorpyrifos (OPPs); permethrin, alpha-cypermethrin and deltamethrin (Pyrs) were selected according to their use as chemotherapeutants in the aquaculture industry. Different parameters affecting extraction efficiency such as fibre coating, agitation, pH and extraction time profiles were investigated. An experimental central composite design (alpha = 1) and desirability functions were used for the simultaneous optimization of extraction temperature and sample volume. Finally, a method based on direct SPME in 40 min at 75 degrees C using 100-microm-thick poly(dimethyl)siloxane (PDMS) fibre and 20 mL of sample volume is proposed. The method was validated, exhibiting good linearity, precision and accuracy parameters with picogram per millilitre LODs. The proposed methodology was applied to determine the ultratrace levels of OPPs and Pyrs in aquaculture-seawater samples by the standard addition approach, which proved to be reliable and sensitive, in addition to requiring only small amounts of sample.     

A multiplier theorem using the Schechter's method of interpolation

Let m be a measurable bounded function and let us assume that there exists a bounded functions S so that m(ξ)S(ξ)^it−1 is a Fourier multiplier on L^p uniformly in . Then, using the analytic interpolation theorem of Stein, one can show that necessarily m is a L^p multiplier. The purpose of this work is to show that under the above conditions, it holds that, for every , m(log S)^kM_p. The technique is based on the Schechter's interpolation method.