New Method For Selective Determination Research Articles

A Simple Method for Melatonin Determination in the Presence of High Levels of Tryptophan using an Unmodified Carbon Paste Electrode and Square Wave Anodic Stripping Voltammetry

AbstractElectrochemical determination of melatonin in the presence of tryptophan is a challenge because of the coincidence of voltammetric signals of these compounds when executing a voltammetric technique. The new method for selective determination of melatonin based on the square wave anodic stripping voltammetry determination of an electroactive product of melatonin was suggested here. This product is produced by previously applied positive pre‐potential to a carbon paste electrode, immersed in the test solution. By this means, the electrochemical signal of melatonin was separated effectively from that of tryptophan, making it possible to determine melatonin in the presence of a high concentration of tryptophan. The effect of important parameters on electrode performance was studied and optimized. The optimum response was obtained at pH=2 and utilizing the pre‐potential magnitude of +0.8 V, applied for 10 s. A linear relationship was found between peak current intensity and melatonin concentrations over the range of 5.00×10−7 to 8.00×10−5 mol L−1. A detection limit of 8.30×10−8 mol L−1 was calculated for the method (S/N=3). The selectivity of the method was considerably high, because of the independence of melatonin signal to the presence of higher amounts of some potentially interfering agents such as ascorbic acid, tryptophane glucose, etc. As an analytical application, the proposed sensor was used for the determination of melatonin in pharmaceutical and food samples.

A new method for selective determination of creatinine using smartphone-based digital image

A new method for selective determination of creatinine using smartphone-based digital image

Raffinose Capped Silver Nanoparticles: A New Localized Surface Plasmon Resonance Based Sensor for Selective Quantification of Cr(VI) in Waste Waters.

In this study, a new method for selective determination of Cr(VI) in water samples at pH 4 is presented using raffinose capped silver nanoparticles (Ag/Raff NPs) as an optical sensor. The method is based on the variation of LSPR absorption band intensity as a result of electrostatic interaction between the negatively charged Ag/Raff NPs and positive Cr(III) ions, in-situ produced by chemical reduction of Cr(VI) with ascorbic acid, combined with the fast kinetics of Cr(III) coordination to the –OH groups of the capping agent on the nanoparticle surface, further causing the nanoparticle aggregation. The calibration curve for Cr(VI) is linear in the range 2.5–7.5 μmol L−1, the limit of quantification achieved is 1.9 μmol L−1, and values of relative standard deviation vary from 3 to 5% for concentration level 1.9–7.5 μmol L−1. The interference studies performed in the presence of various metal ions show very good selectivity of Ag/Raff NPs toward Cr(VI) species. The added–found method is used to confirm the accuracy and precision of developed analytical approach.

A dynamic gas extraction-assisted paper-based method for colorimetric determination of bromides

A new method for selective determination of bromides in natural waters, foodstuffs and pharmaceuticals has been developed.

A simple one-pot synthesis of highly fluorescent nitrogen-doped graphene quantum dots for the detection of Cr(vi) in aqueous media

A new method for selective determination of Cr(VI) in environmental water samples was developed based on its quenching effect on the fluorescent N-doping graphene quantum dots (N-GQDs). The N-GQDs were synthesized by a simple one-step method using citric acid as the carbon source and ammonia as the nitrogen source with a 65% yield, showing that mass production of the N-GQDs is possible. The obtained N-GQDs with oxygen-rich functional groups exhibited a strong blue emission with a quantum yield of 18.6%, which was 7 times greater than that of graphene quantum dots (GQDs). Due to the selective coordination to Cr(VI), the N-GQDs can be used as a green and facile sensing platform for label-free sensitive and selective detection of Cr(VI) ions in aqueous solution and real water samples. Compared to GQDs, the N-GQDs as a fluorescent probe promises much improved selectivity for sensing of Cr(VI). The N-GQDs fluorescence probe shows a sensitive response to Cr(VI) in a wide concentration range of 0–140 μM with a detection limit of 40 nM. The N-GQDs-based fluorescence method was successfully used to selectively detect Cr(VI), and discriminate it and Cr(III) as well in aqueous samples.

Selective Cosmetic Mercury Analysis Using a Silver Ink Screen‐Printed Electrode with Potassium Iodide Solution

AbstractA new method for selective determination of trace mercury has been demonstrated by linear scan voltammetry using silver ink screen printed electrode (AgSPE) in presence of potassium iodide (KI) dissolved 0.05 M H2SO4 solution. At AgSPE, iodide oxidation peak current signal found to be systematically decreased (inhibitory current anodic peak current signal, i$\rm{ {_{pa}^{in}}}$) with increase in the Hg concentrations, [Hg]. This observation is further utilized for construction of new Hg electroanalytical assays in this work. On the AgSPE, Hg inhibitory detection potential found at 0 V vs. Ag/AgCl, which is 720 mV lower than that of unmodified SPE system. Under optimal experimental conditions, i$\rm{ {_{pa}^{in}}}$ signals were linearly increased against [Hg] in the window of 500–4500 ppb (40 μM KI) with a correlation coefficient (r) of 0.9988. The limit of detection (LOD) and limit of quantification (LOQ) were 98 and 318 ppb, respectively. This approach was further utilized to analyze hidden Hg in the cosmetic samples. Real sample assays were consistent with that of result obtained from ICP‐OES, which confirm the applicability of the proposed method for practical applications.

Electroanalytical determination of acetaminophen using nano-TiO 2/polymer coated electrode in the presence of dopamine

We report a new method for selective determination of acetaminophen (AP) in physiological condition. A new hybrid film modified electrode was fabricated using inorganic semiconducting nano-TiO 2 particles and redox active polymer. Redox polymer, poly(acid yellow 9) (PAY) was electrochemically deposited onto nano-TiO 2 coated glassy carbon (GC) electrode. Surface characterizations of modified electrode were investigated by using atomic force microscope and scanning electron microscope. The PAY/nano-TiO 2/GC hybrid electrode shows stable redox response in the pH range 1–12 and exhibited excellent electrocatalytic activities towards AP in 0.1 M phosphate buffer solution (pH 7.0). Consequently, a simple and sensitive electroanalytical method was developed for the determination of AP. The oxidation peak current was proportional to the concentration of acetaminophen from 1.2 × 10 −5 to 1.20 × 10 −4 M and the detection limit was found to be 2.0 × 10 −6 M (S/N = 3). Possible interferences were tested and evaluated that it could be possible to selective detection of AP in the presences of dopamine, nicotinamide adenine dinucleotide (NADH), ascorbic acid and uric acid. The proposed method was used to detect acetaminophen in commercial drugs and the obtained results are satisfactory.

Laccase-catalyzed oxidation and intramolecular cyclization of dopamine: A new method for selective determination of dopamine with laccase/carbon nanotube-based electrochemical biosensors

This study demonstrates a new electrochemical method for the selective determination of dopamine (DA) with the coexistence of ascorbic acid (AA) and 3,4-dihydroxyphenylacetic acid (DOPAC) with laccase/multi-walled carbon nanotube (MWNT)-based biosensors prepared by cross-linking laccase into MWNT layer confined onto glassy carbon electrodes. The method described here is essentially based on the chemical reaction properties of DA including oxidation, intramolecular cyclization and disproportionation reactions to finally give 5,6-dihydroxyindoline quinone and on the uses of the two-electron and two-proton reduction of the formed 5,6-dihydroxyindoline quinone to constitute a method for the selective determination of DA at a negative potential that is totally separated from those for the redox processes of AA and DOPAC. Instead of the ECE reactions of DA with the first oxidation of DA being driven electrochemically, laccase is used here as the biocatalyst to drive the first oxidation of DA into its quinone form and thus initialize the sequential reactions of DA finally into 5,6-dihydroxyindoline quinone. In addition, laccase also catalyzes the oxidation of AA and DOPAC into electroinactive species with the concomitant reduction of O 2. As a consequence, a combinational exploitation of the chemical properties inherent in DA and the multifunctional catalytic properties of laccase as well as the excellent electrochemical properties of carbon nanotubes substantially enables the prepared laccase/MWNT-based biosensors to be well competent for the selective determination of DA with the coexistence of physiological levels of AA and DOPAC. This demonstration offers a new method for the selective determination of DA, which could be potentially employed for the determination of DA in biological systems.

Selective detection of plasma low molecular weight heparin concentration with ultraviolet emission spectroscopy

Objectives: An increasing number of patients undergoing cardiac surgery are pre-treated with low molecular-weight (2–6kDa) heparins (LMWH) with a longer half-life time than unfractioned (10–15kDa) heparins (UFH). In contrast to UFH, LMWH cannot be detected by routine methods and neutralized by protamine. In addition, regular UFH in use contain a considerable amount of LMWH. In this study, a new method for selective determination of UFH, LMWH and heparin-protamine complexes in plasma using ultraviolet (UV)-fluorescence spectroscopy is presented.