Capabilities and limitations of dispersive liquid-liquid microextraction with solidification of floating organic drop for the extraction of organic pollutants from water samples.

Dispersive liquid-liquid microextraction with solidification of floating organic drop (DLLME-SFO) is one of the most interesting sample preparation techniques developed in recent years. Although several applications have been reported, the potentiality and limitations of this simple and rapid extraction technique have not been made sufficiently explicit. In this work, the extraction efficiency of DLLME-SFO for pollutants from different chemical families was determined. Studied compounds include: 10 polycyclic aromatic hydrocarbons, 5 pesticides (chlorophenoxy herbicides and DDT), 8 phenols and 6 sulfonamides, thus, covering a large range of polarity and hydrophobicity (LogKow 0-7, overall). After optimization of extraction conditions using 1-dodecanol as extractant, the procedure was applied for extraction of each family from 10-mL spiked water samples, only adjusting sample pH as required. Absolute recoveries for pollutants with LogKow 3-7 were >70% and recovery values within this group (18 compounds) were independent of structure or hydrophobicity; the precision of recovery was very acceptable (RSD<12%) and linear behavior was observed in the studied concentration range (r(2)>0.995). Extraction recoveries for pollutants with LogKow 1.46-2.8 were in the range 13-62%, directly depending on individual LogKow values; however, good linearity (r(2)>0.993) and precision (RSD<6.5%) were also demonstrated for these polar solutes, despite recovery level. DLLME-SFO with 1-dodecanol completely failed for extraction of compounds with LogKow≤1 (sulfa drugs), other more polar extraction solvents (ionic liquids) should be explored for highly hydrophilic pollutants.

Determination of carbofuran in surface water and biological tissue by sol-gel immunoaffinity extraction and on-line preconcentration/HPLC/UV analysis.

A selective and simple analytical method for the trace level determination of carbofuran in complex environmental and biological samples was developed based on immunoaffinity extraction (IAE) followed by on-line preconcentration and HPLC/UV analysis of the purified extract. The immunosorbent for IAE was prepared by sol-gel encapsulation of monoclonal anti-carbofuran antibodies, and was fully characterized for capacity, repeatability, binding strength, binding kinetics and cross-reactivity. Method performance was evaluated with two different types of difficult samples: dam water and methanolic extracts of epithelial cervical-uterine tissue. Linear behavior and quantitative recoveries were obtained from the analysis of samples spiked with carbofuran at 0.2-4 ng/mL (dam water, 50 mL samples) and 10-40 ng/mL (biological tissue extract, 2 mL samples). RSD (n=7) and detection limits were, respectively, 10.1% (spike 0.40 ng/mL) and 0.13 ng/mL for dam water; 8.5% (spike 20 ng/mL) and 5 ng/mL for the biological tissue extract. The excellent sample purification achieved with the IAE column allows precise and accurate determination of carbofuran in complex matrices, even when using non-selective UV detection in the chromatographic analysis.

Speciation and transformation pathways of chlorophenols formed from chlorination of phenol at trace level concentration.

Trace organic precursors remaining in water after primary treatment can originate a variety of toxic disinfection by-products during chlorination. Therefore, knowledge of conditions leading to their persistence or transformation in chlorinated media is crucial for human health protection. Using phenol as model compound at trace level (50 ppb), the short term formation and degradation of chlorophenols (CPs) in plain water and buffered water (pH 4.8, 7 and 9) treated with typical chlorine doses (1-5 ppm) was investigated. Total phenol consumption and quantitative degradation of formed CPs occurred in < or =5h with 5 ppm chlorine in plain water and alkaline buffer, and with 1 ppm chlorine in phosphate buffer of pH 7. The enhanced reactivity in this buffer was attributed to high ionic strength (0.18 M). On the contrary, phenol was only slowly transformed to monochlorophenols (MCPs) in acidic media. Analysis of phenol and CPs concentration profiles indicated the coexistence of two competing reaction pathways in neutral and alkaline conditions: 1) successive ortho-para chlorination of aromatic ring up to 2,4,6-trichlorophenol followed by ring cleavage, 2) direct oxidation of MCPs to rapidly degradable oxygenated aromatics (dihydroxybenzenes, benzoquinones). Ionic strength and pH had some influence on preferred pathway but chlorine dose was determinant.

A method for the analysis of organophosphorus pesticide residues in Mexican axolotl.

A method based on matrix solid-phase dispersion (MSPD) was developed for quantitative extraction of three organophosphorus pesticides (OPPs) from the Mexican axolotl, Ambystoma mexicanum. The determination was carried out using high- performance liquid chromatography (HPLC) with diode array spectrophotometric UV detection (DAD). The MSPD extraction with octadecylsilyl (C18) sorbent combined with a silica gel clean-up and acetonitrile elution was optimised for chlorpyrifos, fenthion and methyl parathion. The method was validated, yielding recovery values higher than 90%. The precision, expressed as the relative standard deviation (RSD), was less than or equal to 6% in muscle samples at spiking levels of 10 and 5 ppm. Linearity was studied from 15 to 60 ppm for chlorpyrifos and fenthion, and from 7.5 to 30 ppm for methyl parathion. The limits of detection (LODs) were found to be less than or equal to 0.5 ppm. This method was applied to the analysis of samples from a chlorpyrifos-exposed axolotl, demonstrating its use as an analytical tool for toxicological studies.

Binding characteristics of bovine serum albumin encapsulated in sol-gel glasses: an alternative for protein interaction studies.

Silica glasses doped with 500-700 microg of bovine serum albumin were prepared by the sol-gel method; two pH conditions (pH 5 and 7) were assayed for protein encapsulation. Both biomaterials showed a highly porous structure, with pore sizes in the range 5-28 nm. Columns packed with the ground biogels were on-line coupled to a C18 HPLC column for evaluation of the entrapped protein binding properties using propranolol. Binding capacities (at saturation) were approximately 3.7 and 7.1 microg of propranolol (drug-protein molar ratios 1.4 and 2.7) for the biogels prepared at pH 5 and 7, respectively. The significant difference indicates increased albumin denaturation upon encapsulation at pH 5. A frontal analysis study was then performed in cartridges packed with biogel prepared at pH 7 to evaluate the protein interaction with naproxen at low concentrations (

Relative influence of the dissolved humic material on the solid-phase extraction efficiency of pesticides from environmental water.

The effect of organic matter on the solid-phase extraction (SPE) efficiency for pesticides belonging to different chemical groups (urea-derivatives, carbamates and triazines) and having different polarities, was simultaneously studied for the first time in pure and simulated water samples. SPE was carried out in precolumns packed with C18 silica or styrene-divinylbenzene copolymer PLRP-S phases on-line coupled to high performance liquid chromatography (HPLC) analysis. Retention factors in water (k'(W)) were estimated for 25 compounds and used for the calculation of the theoretical breakthrough volume (Vb(T)) in pure water. Experimental breakthrough volumes (Vb(E)) were first determined using purified and deionized water as the matrix for selected compounds having Vb(T) < 500 mL; then, the same water with an added humic acid sodium salt (HA) at 0.4-5.6 mg/L of dissolved organic carbon (DOC) content, was used as the matrix for compounds having VbE < 500 mL in pure water. Several polar pesticides showed negative linear or logarithmic Vb(E) curves depending on HA content; their recoveries were also determined in environmental samples having low dissolved organic carbon values, between 0.5-6.4 mg/L. A similar behavior was observed for these compounds in simulated and natural water samples, where DOC concentration and the percolated volume (Vp) mainly determine the solute recoveries values. However, the variation of recoveries as a function of DOC content could be negative or null depending on the two examined conditions (Vp lower or larger than Vb(E) in pure water). Results demonstrated that breakthrough volume must always be considered to correctly interpret the participation of dissolved humic material on the SPE efficiency of organic micropollutants in water.

Sol-gel immunosorbents doped with polyclonal antibodies for the selective extraction of malathion and triazines from aqueous samples.

Sol-gel immunosorbents (IS) prepared by encapsulation of polyclonal antibodies in silica were packed in cartridges and evaluated for selective immunoaffinity extraction (IAE) of malathion and triazines from aqueous samples. Encapsulated atrazine antibodies highly cross-reacted with simazine and propazine but did not recognize prometon and prometryn. No cross-reactivity of malathion antibodies was observed with the closely related metabolites oxomalathion and isomalathion. Mean IS binding capacities per milligram of entrapped antibody were 0.33 nmol of malathion and 0.47 nmol of atrazine (approximately 100 ng each). This capacity remained constant for at least 10 weeks, and the cartridge reusability was excellent (>60 IAE runs); also, high preconcentration factors were feasible because the breakthrough of analytes from IS cartridges did not occur up to the 250 mL sample volumes, provided that the capacity was not surpassed. Simple and rapid methods for determination of malathion or three triazines in surface water were developed using off-line IAE and HPLC-UV. The application to 50 mL dam water samples spiked at approximately 1 ng/mL of pesticides resulted in recoveries of approximately 90% and RSD < 5% (n=7). LODs for this sample volume (direct injection of IS eluates) were in the range of 0.15-0.50 ng/mL. Lower LODs (0.03-0.1 ng/mL) were achieved by online analysis of whole eluates previously loaded in RP precolumns.

Evaluation and characterization of a commercial immunosorbent cartridge for the solid-phase extraction of phenylureas from aqueous matrices.

The behavior and main characteristics of a commercial immunosorbent (IS) cartridge for the solid-phase extraction of phenylureas are determined in this work. The measured capacity for the analyte-antigen (isoproturon) in a new cartridge is 215 ng and, after more than 100 adsorption-desorption cycles, the remaining capacity still is approximately 70 ng, demonstrating the good stability of the bonded antibody and the interesting possibility of extensive cartridge reuse. Only isoproturon and diuron are specifically retained in this sorbent. The weak nonspecific retention of other pesticides, including other phenylureas, can be avoided by increasing the sample volume during the loading step. Thus, a very selective and sensitive method for the determination of isoproturon and diuron in natural and potable waters is developed by loading a 50-mL sample adjusted to pH 7.4 in the IS cartridge, eluting with methanol-water (60:40, v/v), and analyzing the eluate by high-performance liquid chromatography with UV detection. The clean chromatograms, low detection limits (approximately 0.1 micro g/L), and good precision (< 5%) obtained with this rapid and simple method demonstrate that immunoaffinity extraction can be an excellent alternative for sample preparation in the environmental monitoring of particular pesticides in water matrices.