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Spectrophotometric Technique (spectrophotometric + technique)
Selected AbstractsAmperometric Response of Hydrogen Peroxide at Carbon Nanotubes Paste Electrodes Modified with an Electrogenerated Poly(Fe(III)-5-amino-phenantroline).ELECTROANALYSIS, Issue 1 2010Analytical Applications for Glucose Biosensing Abstract This work reports the catalytic activity of a polymer electrogenerated from Fe(III)-5-amino-1,10-phenantroline solution at a carbon nanotubes paste electrode (CNTPE) towards the oxidation and mainly the reduction of hydrogen peroxide. The important role of carbon nanotubes on the generation of poly(Fe(III)-5-amino-1,10-phenantroline) is demonstrated through the comparison with the behavior of graphite paste electrode (CPE). The polymer electrogenerated at CNTPE largely improves the amperometric detection of hydrogen peroxide at ,0.100,V. The analytical application of the resulting electrode is demonstrated in connection with the design of a glucose biosensor based on the deposition of GOx and diluted Nafion on the top of the polymer-modified CNTPE. The quantification of glucose in human serum samples showed a good correlation with the values obtained by the spectrophotometric technique. [source] Fabrication of Nanoporous Copper Film for Electrochemical Detection of GlucoseELECTROANALYSIS, Issue 21 2009Sirilak Sattayasamitsathit Abstract A nanoporous copper film was fabricated on a copper wire by electrodeposition of copper/zinc alloy and chemically etching of zinc. The surface morphology was investigated by SEM. When applied to detect glucose in an amperometric flow injection system the porous copper electrode provided 12 times higher sensitivity than solid copper. It could be continuously used up to 50 times (%RSD=5.7). Different preparations of the porous film provided reproducible responses (P<0.05). Detection of glucose in E. coli cultivation medium compared well with spectrophotometric technique (P<0.05). This simple technique can produce a nanoporous electrode with good performances and can easily be applied to other metals and analytes. [source] Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009Homayoon Bahrami The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an ,-amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual ,-amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4-dimethylpiperazine-2,5-dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some ,-amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the "critical ratio." The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the "delayed autocatalytic behavior" of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first-order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first-order dependence on Mn2+ ions in catalytic pathways. The correspondence of pseudo-order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified "critical ratio" as well as "delayed autocatalytic behavior" concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689,703, 2009 [source] Kinetic study of the ruthenium(VI)-catalyzed oxidation of benzyl alcohol by alkaline hexacyanoferrate(III)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2002A. E. Mucientes The kinetics of the Ru(VI)-catalyzed oxidation of benzyl alcohol by hexacyanoferrate(III), in an alkaline medium, has been studied using a spectrophotometric technique. The initial rates method was used for the kinetic analysis. The reaction is first order in [Ru(VI)], while the order changes from one to zero for both hexacyanoferrate(III) and benzyl alcohol upon increasing their concentrations. The rate data suggest a reaction mechanism based on a catalytic cycle in which ruthenate oxidizes the substrate through formation of an intermediate complex. This complex decomposes in a reversible step to produce ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in a slow step. The theoretical rate law obtained is in complete agreement with all the experimental observations. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 421,429, 2002 [source] In vitro evaluation of sun protection factors of sunscreen agents using a novel UV spectrophotometric techniqueINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 4 2008M. D. Bleasel Synopsis A method for the in vitro determination of low- and high-value sun protection factors (SPF) of sunscreens using artificial substrates and a novel pseudo double beam (PDB) mode of operation of a standard double beam UV spectrophotometer is described. The method allows transmittance to be calculated from detector responses of reference and sample beams measured at different gain levels and facilitates the accurate quantification of low levels of electromagnetic radiation transmitted through highly absorbing samples. The spectrophotometer was modified to hold quartz diffusing plates on which a substrate [TransporeÔ adhesive tape or human stratum corneum obtained from a skin surface biopsy (SSB)] and the sunscreens to be tested were applied. The PDB mode of operation increased the effective linear range of the detector response of the spectrophotometer by a factor of approximately 20000-fold, enabling the in vitro SPF determination technique to be applied to both high and low SPF value sunscreens. Eight commercial sunscreens with known SPF values ranging from 4 to 77, previously determined by in vivo methods, were tested in vitro using both test substrates and correlations between the in vivo and in vitro values were determined. SPF values determined using the in vitro method correlated well with the known in vivo results (TransporeÔ tape, R2 = 0.611; SSB, R2 = 0.7928). The in vitro SPF obtained for one of the tested products differed substantially from the cited in vivo SPF value. Independent in vitro and in vivo re-evaluation of the SPF of this product matched the value predicted by the present method much more closely than the originally cited in vivo value. All determined SPFs were ordered correctly in comparison to in vivo ranking and the technique appeared to correctly identify a sunscreen that had a labelled SPF value that was significantly higher than its true SPF. Résumé Une méthode destinée à déterminer in vitro les facteurs de protection solaire (SPF) d'écrans solaires de faible et haut indice est décrite. Elle met en ,uvre des substrats artificiels et un nouveau mode opératoire reposant sur l'utilisation du pseudo double faisceau (PDB) d'un spectrophotomètre UV double faisceau standard. La méthode permet le calcul de la transmittence à partir des réponses du détecteur de référence et la mesure en simple faisceau à différents niveaux de gain facilitant ainsi la quantification précise des faibles niveaux de radiation électromagnétique (EMR) transmis à travers des échantillons hautement absorbants. Le spectrophotomètre a été modifié de façon à fixer des plaques diffusantes en quartz sur lesquelles un substrat (ruban adhésif Transport TM ou du stratum corneum humain obtenu à partir de biopsie de surface de peau (SSB) et les écrans solaires testés ont été appliqués. Le mode opératoire PTB augmente la gamme linéaire effective de la réponse du détecteur du spectrophotomètre d'un facteur approximatif 20.000 permettant, à cette technique de détermination des SPF in vitro, d'être appliquée à la fois sur les écrans solaires de haut et bas SPF. Huit écrans solaires commerciaux de SPF connus allant de 4 à 77, préalablement déterminés par des méthodes in vivo, ont été testés in vitro en utilisant les deux substrats, et les corrélations entre les valeurs in vivo et in vitro ont été déterminées. Les valeurs SPF déterminées en utilisant la méthode in vitro est bien corrélée avec les résultats in vivo connus (ruban transport, R2 = 0.611; SSB, R2 = .7928). Le SPF in vitro pour l'un des produits testés diffère fortement des valeurs SPF citées in vivo. Une réévaluation indépendante des SPF in vitro et in vivo de ce produit ajuste la valeur prédite par la présente méthode de façon beaucoup plus proche que la valeur originale citée in vivo. Tous les SPF ainsi déterminés sont ordonnés correctement en comparaison au classement in vivo et la technique semble identifier correctement un écran solaire qui possède un SPF libellé significativement plus haut que son vrai SPF. [source] Cerebral near infrared spectroscopy for the measurement of indocyanine green elimination in cirrhosisALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 7 2000Therapondos Background: Indocyanine green (ICG) clearance is a useful indicator of hepatic function but most measurement methods are invasive. Aim: To validate a less invasive technique using cerebral near infrared spectrophotometry (NIRS) to measure ICG elimination, and to compare it with the established methods for the determination of ICG clearance in a group of normal controls and patients with cirrhosis. Method: NIRS was used to measure ICG elimination in 41 cirrhotic patients and nine healthy volunteers. The first 13 of the cirrhotic patients also had their ICG clearance measured by the conventional spectrophotometric technique. Results: NIRS ICG elimination rate (ICG-k) and spectrophotometry ICG-k values correlated strongly (r= 0.828, P < 0.001, n=13). There was a significant reduction in the mean NIRS-k in cirrhotic patients and within Child,Pugh classes A, B, and C (P < 0.001). Conclusion: Measurement of ICG elimination by the NIRS method is at least as reliable as the conventional spectrophotometric technique in normals and in patients with cirrhosis. This technique merits further development for use as a bedside, less invasive liver function test. [source] Monitoring of pacemaker induced changes in cardiac output with inspired to endtidal oxygen difference in paediatric cardiac surgery patientsPEDIATRIC ANESTHESIA, Issue 2 2001Jan Bengtsson MD Methods:,Fourteen children aged 4,15 months were studied after corrective cardiac surgery. Heart rate was increased by 20% with an external pacemaker. Cardiac output (CO) was measured with thermodilution. Oxygen saturation was measured in systemic artery (SaO2), central vein (ScvcO2) and pulmonary artery (SvO2). Inspiratory to endtidal oxygen difference (FI - ETO2) was measured using a paramagnetic technique. SvO2 was measured continuously using a spectrophotometric technique. Results:,CO increased in three patients and decreased in 11 patients during pacing. Regression between ,CO and ,(1/Sa-vO2), ,(FI - ETO2/Sa-vO2), ,(FI - ETO2/Sa-cvcO2) showed r=0.70, r=0.76 and r=0.75, respectively. ,CO exceeded 10% in 17 of 26 interventions. Changes in FI - ETO2 of equal direction as changes in CO occurred in 12 of these 17 interventions. Conclusions:,Estimations of CO changes, based on SvO2, can be enhanced if changes in FI - ETO2 are also measured. ScvcO2 instead of SvO2 gives equivalent results. Sudden changes in FI - ETO2 after pacemaker initiation or termination can predict the direction of CO changes. [source] | |||||||||||||