SURFACE MODIFICATION OF ELECTRODES FOR AMPEROMETRIC BIOSENSORS IN ANALYTICAL-CHEMISTRY

Amperometric biosensors based on surface modifications of electrodes are described. Cobalt porphyrins modified on glassy carbon and carbon fiber electrodes can greatly decrease the overpotential and increase the sensitivity of detection due to EC electroc

Heteroscedastic controlled calibration model applied to analytical chemistry

In chemical analyses performed by laboratories, one faces the problem of determining the concentration of a chemical element in a sample. In practice, one deals with the problem using the so-called linear calibration model, which considers that the errors associated with the independent variables are negligible compared with the former variable. In this work, a new linear calibration model is proposed assuming that the independent variables are subject to heteroscedastic measurement errors. A simulation study is carried out in order to verify some properties of the estimators derived for the new model and it is also considered the usual calibration model to compare it with the new approach. Three applications are considered to verify the performance of the new approach. Copyright (C) 2010 John Wiley & Sons, Ltd.

Zhurnal analiticheskoĭ khimii = Journal of analytical chemistry /

Latest issue consulted: T. 42, vyp. 12 (dek. 1987).

Gas-Phase Transformation of Phosphatidylcholine Cations to Structurally Informative Anions via Ion/Ion Chemistry

Gas-phase transformation of synthetic phosphatidylcholine (PC) monocations to structurally informative anions is demonstrated via ion/ion reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). Two synthetic PC isomers, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PC16:0/18:1) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (PC18:1/16:0), were subjected to this ion/ion chemistry. The product of the ion/ion reaction is a negatively charged complex, \[PC + PDPA - H](-). Collisional activation of the long-lived complex causes transfer of a proton and methyl cation to PDPA, generating \[PC - CH3](-). Subsequent collisional activation of the demethylated PC anions produces abundant fatty acid carboxylate anions and low-abundance acyl neutral losses as free acids and ketenes. Product ion spectra of \[PC - CH3](-) suggest favorable cleavage at the sn-2 position over the sn-1 due to distinct differences in the relative abundances. In contrast, collisional activation of PC cations is absent of abundant fatty acid chain-related product ions and typically indicates only the lipid class via formation of the phosphocholine cation. A solution phase method to produce the gas-phase adducted PC anion is also demonstrated. Product ion spectra derived from the solution phase method are similar to the results generated via ion/ion chemistry. This work demonstrates a gas-phase means to increase structural characterization of phosphatidylcholines via ion/ion chemistry. Grant Number ARC/CE0561607, ARC/DP120102922

Analytical strategies for the comprehensive profiling of histone post translational modifications by mass spectrometry and implications for functional analyses

Le long bio-polymère d'ADN est condensé à l’intérieur du noyau des cellules eukaryotes à l'aide de petites protéines appelées histones. En plus de leurs fonctions condensatrices,ces histones sont également la cible de nombreuses modifications post-traductionnelles(MPT), particulièrement au niveau de leur section N-terminale. Ces modifications réversibles font partie d’un code d’histones épi-génétique transmissible qui orchestre et module dynamiquement certains événements impliquant la chromatine, tels l’activation et la désactivation de gènes ainsi que la duplication et la réparation d’ADN. Ces modifications sont impliquées subséquemment dans la signalisation et la progression de cancers, tels que la leucémie. En conséquence, l'élucidation des modifications d’histones est importante pour comprendre leurs fonctions biologiques. Une méthodologie analytique a été mise au point en laboratoire pour isoler, détecter, et quantifier les MPT d’histones en utilisant une approche rapide à deux volets à l’aide d’outils bioinformatiques spécialisés. La méthodologie développée en laboratoire a été validée en utilisant des histones de souche sauvage ainsi que deux types d’histones mutants déficients en enzymes acétyltransferase. Des trois sources d’histones utilisées, la seule MPT qui a démontré un changement significatif est l’acétylation de l’histone H3 à lysine 56 (H3K56ac). L’expression et la stoechiométrie de cette MPT, issue de cellules de souche sauvage et de cellules mutantes, ont été déterminées avec précision et comparées. Les fonctions de balayage polyvalentes d'un instrument à trappe ionique quadrupôle linéaire hybride ont été utilisées pour améliorer la détection de protéines intactes. Le mode de balayage « enhanced multiply charged » (EMC) a été modifié pour contenir et détecter les ions de protéines intactes situées dans la trappe ionique linéaire. Ce mode de balayage nommé « targeted EMC » (tEMC) a permis de quadrupler le niveau de sensibilité (signal/interférence), et quintupler la résolution du mode de balayage conventionnel. De plus, la capacité de séparation des charges du tEMC a réduit de façon significative les effets de « space charge » dans la trappe ionique linéaire. La résolution supérieure du mode tEMC a permis de différencier plusieurs isoformes modifiées, particulièrement pour l’histone H3. L’analyse des peptides d’histones trypsiques à l’aide du mode de balayage « MRM » a permis le séquençage et la quantification de MPT avec un haut degré de précision. La seule MPT qui était sous-exprimée entre l’histone de souche sauvage et le mutant DOT1L fut la méthylation de l’histone H3 lysine 79(H3K79me1). Les effets de deux inhibiteurs d’enzymes HDAC (HDACi) sur l’expression de MPT d’histone ont été évalués en utilisant la méthodologie analytique mentionnée. Les histones extraites de cellules normales et cancéreuses ont été exposées à du Vorinostat(SAHA) ou du Entinostat (MS-275) pour une période de 24 à 72 heures. Deux histones furent principalement affectées, soit H3 et H4. Étonnamment, les mêmes effets n'ont pas été détectés lorsque les cellules normales ont été traitées avec le HDACi pour une période de 48 à 72 heures. Une méthode absolue de quantification avec une courbe d’étalonnage a été développée pour le peptide H3K56ac. Contrairement à certaines publications, nos résultats démontrent que cette MPT est présente dans les cellules mammifères avec une stoechiométrie très basse (< 0,1%) et n'est pas surexprimée de façon significative après le traitement au HDACi.

Development of an Analytical Methodology for Quantification of Strong Acid in Diesel Oil

Many factors can affect the quality of diesel oil, in particular the degradation processes that are directly related to some organosulfur compounds. During the degradation process, these compounds are oxidized into their corresponding sulfonic acids, generating a strong acid content during the process. p-Toluene sulfonic acid analysis was performed using the linear sweep voltammetry technique with a platinum ultramicroelectrode in aqueous solution containing 3 mol L(-1) potassium chloride. An extraction step was introduced prior to the voltammetric detection in order to avoid the adsorption of organic molecules, which inhibit the electrochemical response. The extraction step promoted the transference of sulfonic acid from the diesel oil to an aqueous phase. The method was accurate and reproducible, with detection and quantification limits of 5 ppm and 15 ppm, respectively. Recovery of sulfonic acid was around 90%.

Graphite-silicone rubber composite electrode: Preparation and possibilities of analytical application

Composite electrodes were prepared using graphite powder and silicone rubber in different compositions. The use of such hydrophopic materials interned to diminish the swallowing observed in other cases when the electrodes are used in aqueous solutions for a long time. The composite was characterized for the response reproducibility, ohmic resistance, thermal behavior and active area. The voltammetric response in relation to analytes with known voltammetric behavior was also evaluated, always in comparison with the glassy carbon. The 70% (graphite, w/w) composite electrode was used in the quantitative determination of hydroquinone (HQ) in a DPV procedure in which a detection limit of 5.1 x 10(-8) mol L-1 was observed. HQ was determined in a photographic developer sample with errors lower then 1% in relation to the label value. (c) 2007 Elsevier B.V. All rights reserved.

Analytical Potentialities of Carbon Nanotube/Silicone Rubber Composite Electrodes: Determination of Propranolol

A new composite electrode based on multiwall carbon nanotubes (MWCNT) and silicone-rubber (SR) was developed and applied to the determination of propranolol in pharmaceutical formulations. The effect of using MWCNT/graphite mixtures in different proportions was also investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization of different electrode compositions. Propranolol was determined using MWCNT/SR 70% (m/m) electrodes with linear dynamic ranges up to 7.0 mu molL(-1) by differential pulse and up to 5.4 mu molL(-1) by square wave voltammetry, with LODs of 0.12 and 0.078 mu molL(-1), respectively. Analysis of commercial samples agreed with that obtained by the official spectrophotometric method. The electrode is mechanically robust and presented reproducible results and a long useful life.

Diagnostics for the Developing World: Microfluidic Paper-Based Analytical Devices

Microfluidic paper-based analytical devices (mu PADs) are a new class of point-of-care diagnostic devices that are inexpensive, easy to use, and designed specifically for use in developing countries. (To listen to a podcast about this feature, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.)

On the molecular mass of the extracellular hemoglobin of Glossoscolex paulistus: Analytical ultracentrifugation reexamination

The giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) is constituted by Subunits containing heme groups with molecular masses (M) in the range of 15 to 19 kDa, monomers of 16 kDa (d), and trimers of 51 to 52 kDa (abc) linked by nonheme structures named linkers of 24 to 32 kDa (L). HbGp is homologous to Lumbricus terrestris hemoglobin (HbLt). Several reports propose M of HbLt in the range of 3.6 to 4.4 MDa. Based on subunits M determined by mass spectrometry and assuming HbGp stoichiometry of 12(abcd)(3)L(3) (Vinogradov model) plus 144 heme groups, a Value of M for HbGp oligomer of 3560 kDa can be predicted. This Value is nearly 500 kDa higher than the unique HbGp M Value reported in the literature. In the current work, sedimentation velocity analytical ultracentrifugation (AUC) experiments were performed to obtain M for HbGp in oxy and cyano-met forms. s(20,w)(0), values of 58.1 +/- 0.2 S and 59.6 +/- 0.2 S, respectively, for the two oxidation forms were obtained. The ratio between sedimentation and diffusion coefficients supplied values for M of approximately 3600 100 and 3700 100 kDa for oxy and cyano-met HbGp forms, respectively. An independent determination of the partial specific volume, V(bar), for HbGp was performed based on density measurements, providing a value of 0.764 +/- 0.008, in excellent agreement with the estimates from SEDFIT software. Our results show total consistency between M obtained by AUC and recent partial characterization by mass spectrometry. Therefore, HbGp possesses M very close to that of HbLt, suggesting an oligomeric assembly in agreement with the Vinogradov model. (c) 2008 Elsevier Inc. All rights reserved.

Analytical Assessment of a Home Made Capillary Electrophoresis Equipment with Linear Charge Coupled Device for Visible Light Absorption Detection in the Determination of Food Dyes

The performance of modular home made capillary electrophoresis equipment with spectrophotometric detection, at a visible region by means of a miniaturized linear charge coupled device, was evaluated for the determination of four food dyes. This system presents a simple but efficient home made cell detection scheme. A computer program that converts the spectral data after each run into the electropherograms was developed to evaluate the analytical parameters. The dyes selected for analytical evaluation of the system were Brilliant Blue FCF, Fast Green FCF, Sunset Yellow FCF, and Amaranth. Separation was carried out in a 29cm length and 75 mu m I.D fused silica capillary, using 10mmolL-1 borate buffer at pH 9, with separation voltage of 7.5kV. The detection limits for the dyes were between 0.3 and 1.5mgL-1 and the method presented adequate linearity over the ranges studied, with correlation coefficients greater than 0.99. The method was applied for determination and quantification of these dyes in fruit juices and candies.

Comparison of the analytical performance of electrophoresis microchannels fabricated in PDMS, glass, and polyester-toner

This paper compares the analytical performance of microchannels fabricated in PDMS, glass, and polyester-toner for electrophoretic separations. Glass and PDMS chips were fabricated using well-established photolithographic and replica-molding procedures, respectively. PDMS channels were sealed against three different types of materials: native PDMS, plasma-oxidized PDMS, and glass. Polyester-toner chips were micromachined by a direct-printing process using an office laser printer. All microchannels were fabricated with similar dimensions according to the limitations of the direct-printing process (width/depth 150 mu m/12 mu m). LIF was employed for detection to rule out any losses in separation efficiency due to the detector configuration. Two fluorescent dyes, coumarin and fluorescein, were used as model analytes. Devices were evaluated for the following parameters related to electrophoretic separations: EOF, heat dissipation, injection reproducibility, separation efficiency, and adsorption to channel wall.

Development and validation of an analytical method by RP-HPLC for quantification of sibutramine hydrochloride in pharmaceutical capsules

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Analytical method for determination of nitric oxide in zebrafish larvae: Toxicological and pharmacological applications

Zebrafish are currently used at various stages of the drug discovery process and can be a useful and cost-effective alternative to some mammalian models. Nitric oxide (NO) plays an important role in physiology of zebrafish. The availability of appropriate analytical techniques to quantify the NO is crucial for studying its role in physiological and pathological conditions. This work aimed at establishing a high-performance liquid chromatography method for determination of NO levels in zebrafish larvae. Attempts were also made to assess the normal levels of NO at the first days postfertilization and the possible changes under pathological conditions. The method validation was quantitatively evaluated in terms of sensitivity, specificity, precision, accuracy, linearity, and recovery. NO levels from zebrafish larvae at the first days postfertilization and larvae challenged to N(G)-nitro-L-arginine methyl ester, sodium nitroprusside, Escherichia coil lipopolysaccharide, and copper sulfate were analyzed. The samples were derivatized with 2,3-diaminonaphthalene, and fluorescence detection was used for the indirect determination of NO. The method showed a good performance for all validation parameters evaluated and was efficient to monitor changes in NO concentration under physiological and pathophysiological conditions. This method might represent a powerful tool to be applied in NO studies with zebrafish larvae. (C) 2011 Elsevier Inc. All rights reserved.

Essential steps to providing reliable results using the Analytical Quality Assurance Cycle

Considering how demand for quality assurance (QA) has grown in analytical laboratories, we show the trends in analytical science, illustrated through international standard ISO/IEC 17025, validation, measurements of uncertainty, and quality-control (QC) measures. A detailed review of the history of analytical chemistry indicates that these concepts are consistently used in laboratories to demonstrate their traceabilities and competences to provide reliable results. We propose a new approach for laboratory QA, which also develops a diagram to support routine laboratories (which generally apply a quality system, such as ISO/IEC 17025) or research laboratories (that have some difficult applying this international standard). This approach, called the Analytical Quality Assurance Cycle (AQAC), presents the major QA concepts and the relationships between these concepts in order to provide traceability and reliable results. The AQAC is a practical tool to support the trend towards QA in analytical laboratories. (C) 2012 Elsevier Ltd. All rights reserved.