Resistance inducing agents on the biology and probing behaviour of the greenbug in wheat

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Cathodic stripping voltammetric determination of ceftazidime in urine at a hanging mercury drop electrode

A method was developed for the differential-pulse cathodic stripping voltammetric determination of ceftazidime with a hanging mercury drop electrode using its reduction peak at -0.43 V in Britton-Robinson buffer pH 4.0. The optimum accumulation potential and time were -0.15 V and up to 60 s, respectively. Linear calibration graphs were obtained from 1 x 10(-8) M and 1.5 x 10(-7) M. The limit of determination was calculated to be 5 x 10(-9) M. The coefficient of variation was 4% (n = 7) at 1 x 10(-7) M ceftazidime. The effect of various components of urine on the voltammetric response was studied, and creatinine, uric acid, urea, and glucose were shown to interfere in the method. Ceftazidime bound to human albumin gives a unique stripping peak at -0.48 V. Recoveries of 87% +/- 2% of the ceftazidime (n = 5) were obtained from urine spiked with 1.27 mu g ml(-1) using C-18 solid phase extraction cartridges. (C) 1997 Academic Press.

Determination of brilliant blue FCF in the presence and absence of erythrosine and quinoline yellow food colours by cathodic stripping voltammetry

A study of the voltammetric behaviour of the food colours brilliant blue FCF (C.I. 42090), erythrosine (C. I. 45430) and quinolin e yellow (C. I. 47005) in the pH range 2-10 have been carried out by cathodic stripping voltammetry. At pH 4.5 (acetate buffer) with an accumulation potential of 0 V and accumulation time of 30 s, the voltammograms presented well-defined reduction peaks at potential - 0.76 V for brilliant blue FCF, - 0.85 V for quinoline yellow and - 0.54 V for erythrosine. Linear calibration graphs were obtained from 8 to 80 mug l(-1) brilliant blue, from 4 to 43 mug l(-1) quinoline yellow and from 10 to 70 mug l(-1) erythrosine. The method has been successfully applied to identify and quantify binary mixtures of these dyes and applied for determining brilliant blue FCF in commercial food products.

Silver as internal standard for simultaneous determination of Cd and Pb in whole blood by electrothermal atomic absorption spectrometry

The use of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for Cd and Pb determination in whole blood. The comparison of thermochemical and physicochemical parameters allowed the selection of Ag, Bi, and Tl as internal standard candidates. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte ( axis x), precision and accuracy were used to select Ag as the most appropriate internal standard. Blood samples were diluted (1 + 9) with 0.11% (m/v) Triton X-100 + 1.1% (v/v) HNO3 + 0.28% (m/v) NH4H2PO4 + 10 mug L-1 Ag+. Pyrolysis and atomization temperatures for the optimized heating program were 550 and 1700 degreesC, respectively. Characteristic masses based on integrated absorbance were 1.68 +/- 0.01 pg for Cd and 30.3 +/- 0.1 pg for Pb. The detection limits (DL) were 0.095 +/- 0.001 mug L-1 and 0.86 +/- 0.01 mug L-1 for Cd and Pb, respectively. The mean RSD for all determinations was the same for Cd (13 +/- 9%) with or without Ag as internal standard ( IS). on the other hand, the use of Ag as IS improved the RSD for Pb from 3.6 +/- 4.0% to 2.2 +/- 2.0%. An effective contribution of the internal standard Ag was verified in the recoveries of spiked samples (0.5 mug L-1 Cd2+ and 5.0 mug L-1 Pb2+). The mean recoveries were 81 +/- 8% and 91 +/- 4% for Cd, and 80 +/- 11% and 93 +/- 6% for Pb without and with IS correction, respectively. This is the first application of IS for a simultaneous determination by SIMAAS.

Anodic stripping voltammetric determination of aurothiomalate in urine using a screen-printed carbon electrode

This work describes an electroanalytical method for determining gold(I) thiomalate, aurothiomalate, widely used for treatment of reumatoid arthiritis, using a screen-printed carbon electrode (SPCE). Aurothiomalate (AuTM) was determined indirectly at the same electrode by accumulating it first at -1.5 V vs. printed carbon. At this potential in the adsorbed state, the AuTM is reduced to Au(0), which is then oxidized at two steps at -0.22 V and +0.54 V on SPCE. Using optimized conditions of 60 s deposition time, -1.5 V (vs. printed carbon) accumulation potential, 100 mV s(-1) scan rate, linear calibration graphs can be obtained by monitoring the peak at +0.54 V for AuTM in HCl 0.1 mol L-1 from 1.43 x 10(-6) to 1.55 x 10(-4) mol L-1. A limit of detection obtained was 6.50 x 10(-7) mol L-1, and the relative standard deviation from five measurements of 3.0 x 10(-5) mol L-1 AuTM is 4.5%. The method was successfully applied for AuTM determination in human urine sample.

Cathodic stripping voltammetric determination of cefaclor in pharmaceutical formulations

A sensitive method is described for the determination of cefaclor by cathodic stripping voltammetry at the hanging mercury drop electrode. cefaclor is accumulated at the electrode surface as a mercury salt, which is reduced at -0.67 V. The optimum accumulation potential and accumulation time were +0.15 V and up to 180 s, respectively. Linear calibration graphs were obtained between 3.9 mu g.L-1 to 39 mu g.L-1 and the limit of determination was evaluated to be 1.9 mu g.L-1. The method was applied successfully to the determination of cefaclor in pharmaceutical formulations.

Electrochemical reduction and determination of Cibacron Blue F3GA at poly-L-lysine modified glassy carbon electrode

The oxidation of a reactive dye, Cibacron Blue F3GA, CB, (C.I. 61211), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode occurs in two steps at 2.0 < pH < 10 involving one electron transfer each to the amine group leading to the imide derivative. Stable films of poly-L-lysine (PLL) in the presence of glutaraldehyde (GA) 97.5%:2.5% on glassy carbon electrode can be used to detect low levels of dye using its oxidation peak at +0.75V by voltammetry. Linear calibration graphs were obtained for the CB reactive dye, from 1.0 X 10(-6) to 1.0 X 10(-5) mol L-1 in B-R buffer, pH 2.0, using a pre-concentration off-line during 10 min. The detection limit (3 sigma/slope) was calculated to be 4.5 X 10(-8) mol L-1. Films of PLL can readily be applied for the determination of CB dye bearing aminoanthraquinone as chromophore and chlorotriazinyl as reactive group at concentrations at least 100 times lesser than using a glassy carbon electrode without modification. The method described was applied for the determination of CB dye in tap water and raw water collected from the municipal treatment plant with a recovery of 89.2% +/- 5.4 and 88.0% +/- 6.5, respectively. (c) 2005 Elsevier Ltd. All rights reserved.

Differential pulse polarographic determination of clotrimazole after derivatization with Procion Red HE-3B

Clotrimazole was shown to react at room temperature in Britton Robinson buffer pH 2 with the reactive dye Procion Red HE-3B. The product exhibited a differential pulse polarographic peak at -0.38 V, which was well separated from the peaks of the reactive dye at -0.08, -0.80 and -0.95 V, and this allowed the indirect determination of clotrimazole in the presence of excess of the reactive dye. The method has been applied satisfactorily to the determination of clotrimazole in pharmaceutical formulations, calibration graphs are rectilinear up to at least 40 mug ml(-1). The detection limit was calculated to be 2.6 mug ml(-1) (3 sigma). (C) 2002 Elsevier B.V. B.V. All rights reserved.

STOCHASTIC QUANTIZATION OF FERMIONIC THEORIES - RENORMALIZATION OF THE MASSIVE THIRRING MODEL

Using the Langevin approach for stochastic processes, we study the renormalizability of the massive Thirring model. At finite fictitious time, we prove the absence of induced quadrilinear counterterms by verifying the cancellation of the divergencies of graphs with four external lines. This implies that the vanishing of the renormalization group beta function already occurs at finite times.

Indirect polarographic and cathodic stripping voltammetric determination of cefaclor as an alkaline degradation product

Cefaclor is not reducible at a mercury electrode, but it can be determined polarographically and by cathodic stripping voltammetry as its initial alkaline degradation product which is obtained in high yield by hydrolysis of cefaclor in Britton-Robinson (B-R) buffer pH 10 at 50 degrees C for 30 min (reduction peak at pH 10, -0.70 V). Differential pulse polarographic calibration graphs are linear up to at least 1 x 10(-4) mol l(-1). Recoveries of 93% of the cefaclor (n = 3) were obtained from urine spiked with 38.6 mu g ml(-1) using this polarographic method with 1 ml urine made up to 10 ml with pH 10 buffer. Using cathodic stripping voltammetry and accumulating at a hanging mercury drop electrode at -0.2 V for 30 s, linear calibration graphs were obtained from 0.35 to 40 mu g ml(-1) cefaclor in B-R buffer pH 10. A relative standard deviation of 4.2% (eta = 5) was obtained, and the limit of detection was calculated to be 2.9 ng ml(-1). Direct determination of cefaclor in human urine (1 ml of urine was made up to 10 ml with pH 10 buffer) spiked to 0.39 mu g ml(-1) was made (recovery 98.6%). (C) 1999 Elsevier B.V. B.V. All rights reserved.

Application of a glassy carbon electrode modified with poly(glutamic acid) in caffeic acid determination

Glassy carbon electrodes were coated with films of poly( glutamic acid) ( PG), and the modified electrode proved to be very effective in the oxidation of caffeic acid. The performance of the film was also tested with ascorbic acid, coumaric acid, ferulic acid, sinapic acid and chlorogenic acid. At pH 5.6, all the hydroxycinnamic acids yield a higher peak current intensity when oxidized after incorporation in the PG-modified electrode, and only the oxidation of ascorbic acid exhibits overpotential reduction. At pH 3.5 only caffeic and chlorogenic acid are incorporated in the modified electrode and exhibit a well-defined oxidation wave at +0.51 V and +0.48 V, which is the base for their determination. Linear calibration graphs were obtained from 9 x 10(-6) mol L-1 to 4 x 10(-5) mol L-1 caffeic acid by linear voltammetric scan and from 4 x 10(-6) mol L-1 to 3 x 10(-5) mol L-1 by square wave voltammetric scan. The method was successfully applied to the determination of caffeic acid in red wine samples without interference from other hydroxycinnamic acids or ascorbic acid.

Determination of the relative contribution of phenolic antioxidants in orange juice by voltammetric methods

The electrochemical oxidation of caffeic, chlorogenic, sinapic, ferulic and p-coumaric acids was investigated by cyclic voltammetry on acetate buffer pH 5.6 on glassy carbon electrode and modified glassy carbon electrode. According to their voltammetric behavior, the antioxidant activity of these phenolic acids was evaluated and the results pointed to the following sequence: caffeic acid (E-a = +0.31 V) > chlorogenic acid (+ 0.38 V) > sinapic acid (+ 0.45 V) > ferulic acid (+ 0.53 V) >p-coumaric acid (+ 0.73 V). The results were confirmed by DPPH test, which evidenced the strongest antiradical activity for compounds possessing the cathecol moiety (caffeic and chlorogenic acids). Linear calibration graphs were obtained for their determination at concentrations from 1 x 10(-4) to 1 x 10(-3) mol L-1. The method was applied to orange juice. Selectivity was illustrated by the analysis of caffeic and chlorogenic acids electrodeposited on a glassy carbon electrode previously modified by electrochemical activation in the presence of ascorbic acid. (C) 2003 Elsevier B.V. All rights reserved.

Regeneration of poly-L-lysine modified carbon electrodes in the accumulation and cathodic stripping voltammetric determination of the cromoglycate anion

Cromoglycate is accumulated on a poly-L-lysine (PLL) modified carbon electrode best from pH 4 solution, where it is anionic and the PLL is cationic, and at which pH the cromoglycate gives a good reduction peak at -0.82 V. The PLL film can be regenerated readily by washing the electrode with 3 M sodium hydroxide solution, in which the PLL is deprotonated. Regeneration of the film is not required as frequently when larger amounts of PLL are incorporated into it. This allows standard addition procedures to be carried out without regenerating the electrode. Linear calibration graphs have been obtained typically in the range 0.1 - 1.5 mug ml(-1). Detection limits have been calculated to be 10 ng ml(-1). The standard addition method has been applied satisfactorily to diluted urine solutions. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Electroanalysis and determination of acetaldehyde in fuel ethanol using the reaction with 2,4-dinitrophenylhydrazine

The voltammetric reduction of acetaldehyde was studied in 0.1 M LiOH: LiCl (60: 40 v/v). Welldefined waves can be seen at -1.77 and -1.60 V with the use of hanging mercury and glassy carbon electrodes. Acetaldehyde was shown to react at room temperature with the 2,4-dinitrophenylhydrazine and the product exhibited a differential pulse voltammetric peak at -0.90V, which was well separated from the peaks of the derivative. This allowed the indirect determination of acetaldehyde in the presence of 0.1 M ethanol/tetrabutylammonium perchlorate after 10 min of reaction. Calibration graphs were obtained for 1.00 x 10(-6)-1.00 x 10(-4) M of acetaldehyde. The detection limit is 8.14 x 10(-7) M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment.

Determination of the vinylsulphone azo dye, remazol brilliant orange 3R, by cathodic stripping voltammetry

Remazol brilliant orange 3R shows only a voltammetric peak for the reduction of the azo group. No peak was observed for the reduction of the sulfatoethylsulfone or vinylsulfone reactive groups. The reduction of a pre-protonated ate group involving a two-electron process, gives a hydrate derivative in acidic solution. In alkaline solution the reduction process occurs at more negative potential with the formation of an unstable hydrate compound which decomposes via HN-NH bond cleavage and loss of a sulfate group. Optimum conditions are given for the cathodic stripping voltammetric determination of dir: dye in aqueous solution. The optimum accumulation potential and time were 0 V and up to 60 s, respectively. Linear calibration graphs were obtained from 30 to 300 ng ml(-1) in pH 4 and 6.2 to 62 ng ml(-1) in pH 10. The limit of determination obtained was 1.5 ng ml(-1) (pH 10). The coefficient of variation was 2.6% (n = 7) at 62 ng ml(-1) of the reactive dye. (C) 1999 Elsevier B.V. B.V. All rights reserved.