排序方式: 共有41条查询结果,搜索用时 15 毫秒
1.
An organic-phase biosensor based on paraffin/graphite modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as the source of peroxidase was developed and used for determining hydroquinone in cosmetic creams. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-quinone which electrochemical reduction back to hydroquinone was obtained at a peak potential of -0.22 V. The recovery of hydroquinone from two samples ranged from 99.1 to 104.1% and a rectilinear analytical curve for hydroquinone concentration from 7.5x10(-5) to 1.6x10(-3) M (r=0.9991) were obtained. The detection limit was 8.1x10(-6) M and relative standard deviation was <1.0% for a solution containing 7.3x10(-4) M hydroquinone and 1.0x10(-3) M hydrogen peroxide in 0.10 M tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n=10). The results obtained for hydroquinone in cosmetic creams using the proposed biosensor are in close agreement with those obtained using a Pharmacopoeia procedure at the 95% confidence level. 相似文献
2.
A biosensor based on stearic acid-graphite powder modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as peroxidase source was constructed and applied in organic solvents. Several parameters were studied to evaluate the performance of this biosensor such as stearic acid-graphite powder and tissue composition, type and concentration of supporting electrolyte, organic solvents, water/organic solvent ratio (% v/v) and hydrogen peroxide concentration. After selection of the best conditions, the biosensor was applied for the determination of hydroquinone in cosmetic creams in methanol. At the peroxidase electrode hydroquinone is oxidized in the presence of hydrogen peroxide and the radical formed was reduced back electrochemically at -180 mV vs Ag/AgCl (3.0 mol L(-1) KCl). The reduction current obtained was proportional to the concentration of hydroquinone from 6.2 x 10(-5) to 1.5 x 10(-3) mol L(-1) (r = 0.9990) with a detection limit of 8.5 x 10(-6) mol L(-1). The recovery of hydroquinone from two samples ranged from 98.8 to 104.1% and an RSD lower than 1.0% for a solution containing 7.3 x 10(-4) mol L(-1) hydroquinone and 1.0 x 10(-3) mol L(-1) hydrogen peroxide in 0.10 mol L(-1) tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n = 10) was obtained. 相似文献
3.
A simple flow injection system is proposed for the determination of thiamine in pharmaceutical formulations. The determination is based on the precipitation reaction of thiamine with silicotungstic acid in acidic medium to form a thiamine silicotungstate suspension that is measured at 420 nm. Adding 0.05% (w/v) poly(ethyleneglycol) in the carrier solution (0.5 mol l(-1) hydrochloric acid), an improvement in the sensitivity, repeatability and baseline stability of the flow injection system was obtained. The calibration graph was linear in the thiamine concentration range from 5.0x10(-5) to 3.0x10(-4) mol l(-1) with a detection limit of 1.0x10(-5) mol l(-1). The relative standard deviations for ten successive measurements of 1.0x10(-4) mol l(-1) and 2.5x10(-4) mol l(-1) thiamine were less than 1% and an analytical frequency of 90 h(-1) was obtained. 相似文献
4.
Roberta A. Medeiros Roberto Matos Abdelkader Benchikh Boualem Saidani Catherine Debiemme-Chouvy Claude Deslouis Romeu C. Rocha-Filho Orlando Fatibello-Filho 《Analytica chimica acta》2013
Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CNx) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CNx electrode. Thus, an a-CNx film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L−1 KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CNx electrode were 0.0656 μmol L−1 for DA and 1.05 μmol L−1 for AA, whereas with the BDD electrode these values were 0.283 μmol L−1 and 0.968 μmol L−1, respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CNx electrode in electroanalysis. 相似文献
5.
A flow injection (FI) spectrophotometric method was proposed for the determination of chloride ion in natural waters. The determination of chloride was carried out by reaction with Hg(SCN)2 immobilized in an epoxy resin bead in a solid-phase reactor (SPR) and the thiocyanate ions released were determined spectrophotometrically at 480 nm after complexing reaction with Fe(III). The analytical curve for chloride was linear in the concentration range from 5.6 × 10−5 to 2.2 × 10−4 mol l−1 with a detection limit of 1.4 × 10−5 mol l−1. The relative standard deviation (R.S.D.) was 2.2% for a solution containing 2.2 × 10−4 mol l−1 (n = 10). The simple manifold allows a routine analytical frequency of 100 determinations per hour. The main advantage of the developed method is the 400% reduction of the Hg waste solution generated when compared to conventional methods for chloride determination based on the same spectrophotometric reaction. 相似文献
6.
Djenaine De Souza Lucia Helena Mascaro Orlando Fatibello-Filho 《Journal of Solid State Electrochemistry》2011,15(9):2023-2029
The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver
solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass
ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by
energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the
silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed
that the AgSAE 30/70 contained only one single phase (Ag2Hg3), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect
to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III)
chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and
cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive
area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave
voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric
parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes. 相似文献
7.
M. F. S. Teixeira L. A. Ramos E. Almeida Neves O. Fatibello-Filho 《Analytical and bioanalytical chemistry》2000,367(1):86-89
The construction and the application of a silica gel based carbon-epoxy indicator electrode for the potentiometric determination
of acids and bases are described. The effect of composition of silica gel and carbon-epoxy, slope (mV/pH), linear response
(pH range) and the use for acid-base titrations were investigated. The data obtained for the acid-base titrations were compared
with those obtained using a glass electrode in the same conditions. The electrode showed a linear response in the pH 2 to
13 range with a slope of –40.5 ± 0.4 mV/pH (at 25 °C) and a response time of less than 15 s. The lifetime of the electrode
was higher than one year (over 6000 determinations) with a decrease of only 5% of the initial potentiometric response. The
silica gel based carbon-epoxy electrode showed excellent results in the end-point indication potentiometric titrations in
determination of acids and bases. The miniaturization of the proposed electrode for flow injection analysis was investigated.
Received: 11 August 1999 / Revised: 4 October 1999 / Accepted: 7 October 1999 相似文献
8.
Monteiro Thatyara Oliveira dos Santos Clenilton Costa do Prado Thiago Martimiano Damos Flávio Santos Luz Rita de Cássia Silva Fatibello-Filho Orlando 《Journal of Solid State Electrochemistry》2020,24(8):1801-1809
Journal of Solid State Electrochemistry - A novel label-free photoelectrochemical immunosensor was developed for the determination of prostate-specific antigen (PSA) based on fluorine-doped tin... 相似文献
9.
Geiser G. Oliveira Bruno C. Janegitz Valtencir Zucolotto Orlando Fatibello-Filho 《Central European Journal of Chemistry》2013,11(11):1837-1843
A glassy carbon electrode (GC) containing multiwalled functionalized carbon nanotubes (MWCNTs) immobilized within a dihexadecylhydrogenphosphate film (DHP) is proposed as a nanostructured platform for determination of methotrexate (MTX) concentration (a drug used in cancer treatment) using differential pulse adsorptive stripping voltammetry (DPAdSV). The voltammograms for a MTX solution using MWCNTs-DHP/GC electrode presented an oxidation peak potential at 0.98 V vs. Ag/AgCl (3.0 mol L?1 KCl) in a 0.1 mol L?1 sulphuric acid. The apparent heterogeneous electron transfer rate constant of 0.46 s?1 was calculated. The recovery area of 2.62×10?9 mol cm2 was also obtained. Under the optimal experimental conditions, the analytical curve was linear in the MTX concentration range from 5.0×10?8 to 5.0×10?6 mol L?1, with a detection limit of 3.3×10?8 mol L?1. The MWCNTs-DHP/GC electrode can be easily prepared and was applied for the determination of MTX in pharmaceutical formulations, with results similar to those obtained using a high-performance liquid chromatography comparative method. 相似文献
10.
A flow injection potentiometric procedure for saccharin determination in dietary products is proposed. Saccharin is precipitated as mercurous saccharinate and the excess of the mercurous cation is potentiometrically measured using a silver wire coated with a mercury film as the working electrode. A filter unit is used to avoid contact between the precipitate and the electrode surface. With relocation in the flow manifold, the accumulated precipitate is removed on-line. Sucrose, glucose, aspartame, sodium cyclamate and sodium benzoate do not interfere when present in amounts similar to those observed in commercial products. Results are comparable with those obtained by UV-spectrophotometry and the correlation coefficient between methods is equal to 0.9930. A linear relationship between DeltaE (mV) and the logarithm of saccharin concentration was obtained in the saccharin concentration range 2 x 10(-3) - 1 x 10(-2)M. The sampling frequency is 60/hour and only 0.76 mg of Hg(2+)(2) is consumed in each determination. 相似文献