Square-wave voltammetric determination of primaquine in urine using a multi-walled carbon nanotube modified electrode

The electrochemical process involving primaquine was studied at a glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (MWCNT). The GC/MWCNTs electrode promoted an intense oxidation peak for primaquine, improving signal when compared to the one observed using bare GC as electrode. Besides the increasing in active electrode area, the MWCNTs seemed to provide faster electron transfer. The linear analytical response for primaquine, in the concentration range from 0.1 to 5.0 μmol L−1, was achieved on a supporting electrolyte consisting of Britton-Robinson buffer (0.02 mol L−1; pH 7.00) and KCl (0.25 mol L−1). The quantitative assay using square-wave voltammetry was performed by successive additions of standard into the electrochemical cell, containing the sample, with instrumental limit of detection (LOD) of 7.3 μg L−1 (28 nmol L−1). A procedure involving liquid-liquid extraction and thin-layer chromatography provided selectivity and pre-concentration required for the determination of traces of primaquine in urine samples (LOD of the method of 146 ng L−1). Recoveries in urine samples were statistically similar to the one achieved by HPLC

Determination of Kresoxim-Methyl in Water and in Grapes by High-Performance Liquid Chromatography (HPLC) Using PhotochemicalInduced Fluorescence and Dispersive Liquid-Liquid Microextraction (DLLME)

A high-performance chromatographic method was developed to determine the fungicide kresoxim-methyl. Off-line photochemical derivatization was used to induce the formation of a stable and fluorescent product since the fungicide does not present natural fluorescence. Intense fluorescence at 370/430nm was achieved by treating the analyte in solution at pH 6 to ultraviolet light for 45s. The chromatographic conditions included isocratic elution with 50/ 50% (v/v) acetonitrile/water and the photochemical product appeared at a retention time of 7.2min. The short and long term stabilities of the photoproduct were evaluated and variation of less than 5% was achieved. The limits of detection in water samples and in grapes samples were 0.019mg kg1 and 0.065mg kg1 of kresoxim-methyl residue, respectively. The linear response covered three orders of magnitude up to 10.6mg kg1 of kresoxim-methyl. The robustness was evaluated through a Box–Behnken experimental design showing the insignificance of all factors and their interactions. The potential interference of tebuconazole for the determination of kresoxim-methyl was studied. The use of the dispersive liquid-liquid microextraction (DLLME) allowed recoveries between 80% and 101% depending on concentration with the minimum generation of waste products

Spectrofluorimetry in organized media coupled to second-order multivariate calibration for the determination of galantamine in the presence of uncalibrated interferences

The present article describes the spectrofluorimetric determination of galantamine, a widely usedacetylcholinesterase inhibitor, through excitation–emission fluorescence matrices and second-order calibration. With the purpose of enhancing the fluorescence intensity of this substance, the effect of different organized assemblies was evaluated. Although the interaction of galantamine with different cyclodextrins is weak, it was corroborated that the fluorescence intensity of this pharmaceutical in the presence of -cyclodextrin is increased by a twofold factor. Among the studied micellar media, the anionic surfactant sodium dodecyl sulfate produced the largest signals for the compound of interest (sixfold enhancement), and was selected as auxiliary reagent for the subsequent determinations. The developed approachenabled the determination of galantamine at the ngmL−1 level without the necessity of applying separation steps, and in the presence of uncalibrated interferences. The applied second-order chemometric tools were parallel factor analysis (PARAFAC), unfolded partial least-squares coupled to residual bilinearization (U-PLS/RBL), and multidimensional partial least-squares coupled to residual bilinearization (N-PLS/RBL). The ability of U-PLS/RBL to successfully overcome spectral interference problems is demonstrated. The quality of the proposed method was established with the determination of galantamine in both artificial and natural water samples.Fil: Culzoni, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Aucelio, Ricardo Q.. Pontifícia Universidade Católica do Rio de Janeiro; BrasilFil: Escandar, Graciela Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

High-performance liquid chromatography with fast-scanning fluorescence detection and multivariate curve resolution for the efficient determination of galantamine and its main metabolites in serum

Based on green analytical chemistry principles, an efficient approach was applied for the simultaneous determination of galantamine, a widely used cholinesterase inhibitor for the treatment of Alzheimer's disease, and its major metabolites in serum samples. After a simple serum deproteinization step, second-order data were rapidly obtained (less than 6 min) with a chromatographic system operating in the isocratic regime using ammonium acetate/acetonitrile (94:6) as mobile phase. Detection was made with a fast-scanning spectrofluorimeter, which allowed the efficient collection of data to obtain matrices of fluorescence intensity as a function of retention time and emission wavelength. Successful resolution was achieved in the presence of matrix interferences in serum samples using multivariate curve resolution-alternating least-squares (MCR-ALS). The developed approach allows the quantification of the analytes at levels found in treated patients, without the need of applying either preconcentration or extraction steps. Limits of detection in the range between 8 and 11 ng mL−1, relative prediction errors from 7 to 12% and coefficients of variation from 4 to 7% were achieved.Fil: Culzoni, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; ArgentinaFil: Aucelio, Ricardo Q.. Pontifícia Universidade Católica do Rio de Janeiro; BrasilFil: Escandar, Graciela Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentin

Luminescence imaging and toxicity assessment of graphene quantum dots using in vitro models

Graphene quantum dots (GQDs) have been of high interest due to their size and optical characteristics, which improves when functional groups are added to their borders and defects. In this work, the in vitro toxicity of aqueous dispersion of GQDs (w/wo amino-functionalization) was investigated in two different cellular models (S. cerevisiae and H9c2 cell line). Results in yeast suggest that when at up to 25 % volume concentration, the effect of all tested GQDs was only inhibitory, and, in both cellular models, the toxic effect is rigorously dose-dependent. The comparison of IC50 values of all the tested GQDs reveals no significant variations among them, pointing to non-carbonized citric acid as the more toxic precursor. The obtained data suggest that functionalization makes GQDs less toxic, being the one functionalized with thioacetamide slightly more toxic, followed by the ones functionalized with thiourea and glutathione, respectively. Results confirm that their toxicity is characteristics as a whole, and not as the sum of the toxicity of the precursors. In both models, concentrations up to 2 % showed no significant toxicity. Finally, fluorescence microscopy images suggest that GQDs interact with the cellular membrane and enter in the cell, manifesting fluorescent properties

Determination of thiomersal and mercurial residues by photo-degradation and flow injection analysis with luminescence probing using carbon quantum dots prepared from thiourea

Thiomersal is an organomercurial compound but, despite that, it is widely used in vaccines formulations to inactivate organisms and toxins and to prevent microbial growth during storage and use. In this work, thiomersal (along with traces of mercurial residues) was determined after photo-degradation (using UV and H2O2) to produce Hg2+ that was determined by flow injection analysis using luminescence probing with carbon quantum dots (prepared from citric acid and thiourea). Linear analytical response was observed in the concentration range of 25 to 900 µg L−1 and the method was efficiently applied to the determination of thiomersal in vaccines against hepatitis B and diphtheria-tetanus with recoveries ranging from 93 to 94%

Simple, Direct and Simultaneous Stripping Voltammetric Determination of Lead and Copper in Gasoline Using an In Situ Mercury Film Electrode

An improved procedure is presented to determine Pb(II) and Cu(II) in gasoline using a mercury film electrode generated in situ. The method is based on the reduction of the metal ions at adequate potentials on the glassy carbon electrode, in whose optimized microemulsion medium composition, the ions can be determined directly and simultaneously by differential pulse anodic stripping voltammetry. Good results were obtained in terms of analytical performance and voltammetric wave forms, with two stripping peaks near to -0.420 V and -0.13 V, attributed to Pb(II) and Cu(II), respectively. Linear responses for both metal ions indicated quite low detection limits (2.1x 10(-9) mol L-1 for Pb(II) and 2.4 x 10(-9) mol L-1 for Cu(II)). The method was applied successfully to real gasoline samples, presenting good results for precision (variation coefficients of 12.4% and 10.2%) and accuracy (recoveries ranging from 96.7 to 99.33% and 101.33 to 102 .67%), for Pb(II) and Cu(II), respectively.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Quenching of the Photoluminescence of Gold Nanoclusters Synthesized by Pulsed Laser Ablation in Water upon Interaction with Toxic Metal Species in Aqueous Solution

Sensors for the detection of heavy metal ions in water are in high demand due to the danger they pose to both the environment and human health. Among their possible detection approaches, modulation of the photoluminescence of gold nanoclusters (AuNCs) is gaining wide interest as an alternative to classical analytical methods based on complex and high-cost instrumentation. In the present work, luminescent oxidized AuNCs emitting in both ultraviolet (UV) and visible (blue) regions were synthesized by pulsed laser ablation of a gold target in NaOH aqueous solution, followed by different bleaching processes. High-resolution electron microscopy and energy-dispersive X-ray scattering confirmed the presence of oxygen and gold in the transparent photoluminescent clusters, with an average diameter of about 3 nm. The potentialities of the bleached AuNCs colloidal dispersions for the detection of heavy metal ions were studied by evaluating the variation in photoluminescence in the presence of Cd2+, Pb2+, Hg2+ and CH3Hg+ ions. Different responses were observed in the UV and visible (blue) spectral regions. The intensity of blue emission decreased (no more than 10%) and saturated at concentrations higher than 20 ppb for all the heavy metal ions tested. In contrast, the UV band emission was remarkably affected in the presence of Hg2+ ions, thus leading to signal variations for concentrations well beyond 20 ppb (the concentration at which saturation occurs for other ions). The limit of detection for Hg2+ is about 3 ppb (15 nmol/L), and the photoluminescence intensity diminishes linearly by about 75% up to 600 ppb. The results are interpreted based on the ligand-free interaction, i.e., the metallophilic bonding formation of Hg2+ and Au+ oxide present on the surface of the UV-emitting nanoclusters