Electrochemical sensor based on MIP for highly sensitive detection of 5-hydroxyindole-3-acetic acid carcinoid cancer biomarker in human biological fluids.

An electrochemically synthetized nano-sensor based on molecularly imprinted polypyrrole (MIPPy) was successfully developed for the detection of 5-hydroxyindole-3-acetic acid (5-HIAA) in human biological fluids namely serum, urine, and plasma. The imprinted glassy carbon electrode was prepared by electropolymerisation of pyrrole via cyclic voltammetry (C.V). After completely leaching the imprinted molecules from the polymeric network, complementary cavities are created. The developed MIPPy sensor, under optimized conditions, shows a high sensitivity towards the target molecule (LOQ = 5 × 10-11 M). Moreover, it presents a wide linear response in the range of 5 × 10-11 - 5 × 10-5 M (R2 > 0.999) with a detection limit of 15 × 10-12 M. In order to evaluate the selectivity of the MIPPy film, several structural analogues and compounds forming the real matrices were tested. The obtained results show an excellent recovery rate (between 98.86 and 101.52%) proving the promising application of the proposed nano-sensor in the detection of 5-HIAA in human biological fluids without any significant interference recorded.

ZnFe2O4-chitosan magnetic beads for the removal of chlordimeform by photo-Fenton process under UVC irradiation.

A simple protocol was proposed for the preparation of magnetic chitosan beads ZnFe2O4-CS via a co-precipitation method. The use of synthesized magnetic ZnFe2O4-CS beads as catalyst for the heterogeneous photo-Fenton treatment of chlordimeform insecticide (CDM) was evaluated. The photo-Fenton experiments were carried out with different synthesized catalysts by varying the molar ratio Zn/Fe in chitosan beads, the catalyst concentration and pH. Under optimal conditions using 1 g of ZnFe2O4-CS beads with a molar ratio Zn/Fe = 0.35 and at pHinitial = 3, a real wastewater doped with 20 mg L-1 of CDM was treated and complete removal of the insecticide was achieved after 7 min with a total TOC removal after 2 h of treatment. The generated carboxylic acids and ions during the photo-Fenton process were identified and quantified. The stability of the photocatalytic activity of the best catalyst in terms of pollutant removal, ZnFe2O4-CS(0.35) beads with a molar ratio Zn/Fe equal to 0.35, was satisfactory validated by four consecutive cycles. This optimal catalyst was characterized, before and after use, by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy, X-Ray Powder Diffraction and Vibrating Sample Magnetometry analysis.

Chemical oxidation of a malodorous compound, indole, using iron entrapped in calcium alginate beads.

Iron-alginate beads (Fe-ABs) were successfully prepared by the ion-gelation method, and applied as heterogeneous Fenton catalysts for the removal of a malodorous compound 'indole'. Similarly, copper-enriched alginate beads (Cu-ABs) were synthesized and tested as like-Fenton catalyst, however, their application proved not to be effective for this purpose. Fe-ABs catalysts were characterized by FTIR, SEM, EDS and AAS spectroscopy. Results pointed out that the parameters affecting Fenton catalysis must be carefully chosen to avoid excessive iron release. Under optimal conditions, complete indole removal and considerably high reduction of TOC, without significant leaching was achieved. Indole decay followed a pseudo-first-order kinetics. The absolute rate constant for indole hydroxylation was 3.59×10(9) M(-1) s(-1), as determined by the competition kinetics method. Four reaction intermediates (Isatin, Dioxindole, Oxindole and Anthralinic acid) were identified by ULC/MS/MS analysis. Short-chain aliphatic carboxylic acids like formic, acetic, oxalic, maleic, oxamic and pyruvic acids were identified by ion exclusion chromatography and as end-products. Based on the identified by-products, a plausible mineralization pathway was proposed. Moreover, the catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.

Synthesis of magnetic alginate beads based on Fe3O4 nanoparticles for the removal of 3-methylindole from aqueous solution using Fenton process.

A novel magnetic heterogeneous catalyst has been developed by incorporation of iron(II) and magnetic functionalized nanoparticles Fe3O4 in alginate beads with the aim of using them in the advanced Fenton oxidation of a malodorous compound (3 methyl-indole: 3-MI). The effects of significant operational parameters such as initial pH, oxidant concentration and catalyst amount were investigated and optimized for a better removal of 3-MI at initial concentration of 20mgL(-1). Besides, the catalyst stability was evaluated according to the iron leached into the aqueous solution. Results revealed that the parameters affecting Fenton catalysis must be carefully chosen to avoid excessive iron release. Under optimized conditions, the magnetic catalyst exhibited a good catalytic performance. Total removal of 3 methyl indole and a remarkable organic mineralization, without significant leaching of iron, were attained within 120min at pH 3.0 by using 0.4gL(-1) of Fe-MABs and 9.8mmolL(-1) of H2O2. The novel magnetic catalyst would be of potential application due to its high efficiency, easy recovery and good structural stability.

Preparation and application of a molecularly imprinted polymer for determination of glibenclamide residues.

The performance of a molecularly imprinted polymer (MIP) as selective packing material for solid-phase extraction (SPE) of residual glibenclamide in an industrial process was investigated. MIP was prepared using 4-vinylpyridine as monomer, ethylenedimethacrylate as cross linker, 2,2'-azobis-2-methylpropionitrile as initiator and dimethyl formamide as porogen. Use of acetonitrile as a rebinding solvent allows good recognition of the glibenclamide template. It was found that this polymer can be used for determination of trace levels of glibenclamide with a recovery percentage that could reach 87.1 %. Furthermore, the synthesized MIP showed higher selectivity towards glibenclamide than other compounds such as glimepiride and metformin. The synthesized MIP enabled direct determination of the target contaminant after an enrichment step that allowed quantification of glibenclamide at a concentration as low as 0.016 mg L-1. Combination of high performance liquid chromatography with MIP-SPE could be successfully used for quality control of pharmaceuticals during the cleaning process in the production of dry drug forms.

Gas diffusion flow injection determination of thiomersal in vaccines.

A new simple gas diffusion flow injection method has been developed for the determination of thiomersal in biological samples. The method is based on cold vapor generation of monoatomic mercury from thiomersal reaction with acidic stannous chloride solution (0.6%) acting as reducing agent. The evolved mercury partially diffuses through a Teflon membrane into an acidic permanganate (2.25 × 10(-4) mol L(-1)) acceptor stream, where it is oxidized and re-converted to Hg(II). The resulting decrease in acceptor stream absorbance is sensitively monitored at 528 nm. Flow injection variable parameters such as reagents concentrations, injected volume, reactor length, temperature and flow rate were carefully investigated and optimized. The concentration-response relationship was linear over a concentration range of 1-30 mg L(-1) with a correlation coefficient greater than 0.99 and a good reproducibility (RSD<1.42%, n=6) at 10 mg L(-1). A detection limit of 0.07 mg L(-1) (S/N=3) and a sampling frequency of 5 samples h(-1) were obtained. The method was successfully applied for the determination of thiomersal in different types of vaccines and gave results in close agreement with those found by previously established HPLC method with no significant interference from vaccines matrices.

Removal of rotenone insecticide by adsorption onto chemically modified activated carbons.

The removal of rotenone from synthetic and real wastewaters using modified activated carbons has been investigated. In order to enhance the removal capacity of rotenone, activated carbon was chemically modified through impregnation with NH(3) and (NH(4))(2)S(2)O(8) solutions. The resulting carbons were found to present different surface chemistries, while possessing similar textural properties. The adsorption data obtained at 298 K, on plain and modified carbons were well represented by the Langmuir isotherm model (R(2)>0.997). The highest adsorption capacity (Q(m)=270.3 mg g(-1)) was obtained with the ammonia-treated activated carbon. The relative effect of different surface groups on adsorption capacities were found to be in accordance with the pi-pi dispersive interaction model. The adsorption kinetic models have provided useful insights into rotenone adsorption mechanism. It was concluded that rotenone sorption process followed pseudo-second order model and was controlled by intra-particle diffusion mechanism with a significant contribution of film diffusion. The successful adsorptive removal of rotenone, from real wastewater samples on fixed bed columns, have demonstrated the suitability of this method as an effective alternative solution for the treatment of contaminated wastewaters.

Tartrazine modified activated carbon for the removal of Pb(II), Cd(II) and Cr(III).

A two in one attempt for the removal of tartrazine and metal ions on activated carbon has been developed. The method was based on the modification of activated carbon with tartrazine then its application for the removal of Pb(II), Cd(II) and Cr(III) ions at different pH values. Tartrazine adsorption data were modelled using both Langmuir and Freundlich classical adsorption isotherms. The adsorption capacities qm were 121.3, 67 and 56.7mgg(-1) at initial pH values of 1.0, 6.0 and 10, respectively. The adsorption of tartrazine onto activated carbon followed second-order kinetic model. The equilibrium time was found to be 240min at pH 1.0 and 120min at pH 10 for 500mgL(-1) tartrazine concentration. A maximum removal of 85% was obtained after 1h of contact time. The presence of tartrazine as modifier enhances attractive electrostatic interactions between metal ions and carbon surface. The adsorption capacity for Pb(II), Cd(II) and Cr(III) ions has been improved with respect to non-modified carbon reaching a maximum of 140%. The adsorption capacity was found to be a pH dependent for both modified and non-modified carbon with a greater adsorption at higher pH values except for Cr(III). The enhancement percent of Pb(II), Cd(II) and Cr(III) at different pH values was varied from 28% to 140% with respect to non-modified carbon. The amount of metal ions adsorbed using static regime was 11-40% higher than that with dynamic mode. The difference between adsorption capacities could be attributed to the applied flow rate.

Flow-injection methylene blue-based spectrophotometric method for the determination of peroxide values in edible oils.

A flow-injection method for measuring the peroxide value (PV, mequiv. O2 kg(-1)) in edible oils is described. The technique is based on spectrophotometric monitoring at 660 nm of methylene blue (MB), generated from leucomethylene blue (LMB) oxidation with peroxides present in oil samples. After being optimized, the method was validated in terms of linearity, precision sensitivity and recovery. Linear calibration graph was obtained in the range 0.1-5 mequiv. O2 kg(-1), with a detection limit (S/N=3) of 0.014 mequiv. O2 kg(-1). The precision of the method (R.S.D., n=9) for within and between-days is better than 1.5% and 2.2%, respectively at 0.4 mequiv. O2 kg(-1). The method was applied successfully to the determination of PV in six edible oil samples, and compared to the classical official method. Using the linear regression test, Student's t-test and variance ratio F-test, there was no significant difference between the compared methods. The proposed method is accurate, simple, cheap and could be used to control edible oil rancidity with a high sample throughputs (30 samples h(-1)).

Determination of trimebutine in pharmaceuticals by differential pulse voltammetry at a glassy carbon electrode.

The differential pulse voltammetric (DPV) determination of trimebutine (TMB) was achieved at a glassy carbon electrode in acetonitrile/0.1 M LiClO4. Trimebutine gave two irreversible, diffusion controlled peaks at 740 and 1318 mV versus Ag/AgCl reference electrode, respectively. The second oxidation peak was used to determine trimebutine concentrations in the range 1-50 microg ml(-1) with a detection limit (3sigmam) of 0.3 microg ml(-1). Precision of the method (RSD, n=6) within- and between-days obtained from six determinations at 5 microg ml(-1) was found to be 0.7 and 1.1%, respectively. The method was successfully applied to the quantitation of TMB in granule dosage form (Debridat) and recoveries between 98.4 and 101% were obtained. Excipients did not interfere with the assay and the results agreed well with those determined by previously established HPLC method.

Treatment of electroplating wastewater containing Cu2+, Zn2+ and Cr(VI) by electrocoagulation.

The performance of electrocoagulation, with aluminium sacrificial anode, in the treatment of metal ions (Cu2+, Zn2+ and Cr(VI)) containing wastewater, has been investigated. Several working parameters, such as pH, current density and metal ion concentrations were studied in an attempt to achieve a higher removal capacity. Results obtained with synthetic wastewater revealed that the most effective removal capacities of studied metals could be achieved when the pH was kept between 4 and 8. In addition, the increase of current density, in the range 0.8-4.8 A dm(-2), enhanced the treatment rate without affecting the charge loading, required to reduce metal ion concentrations under the admissible legal levels. The removal rates of copper and zinc were found to be five times quicker than chromium because of a difference in the removal mechanisms. The process was successfully applied to the treatment of an electroplating wastewater where an effective reduction of (Cu2+, Zn2+ and Cr(VI)) concentrations under legal limits was obtained, just after 20 min. The electrode and electricity consumptions were found to be 1 g l(-1) and 32 A h l(-1), respectively. The method was found to be highly efficient and relatively fast compared to conventional existing techniques.