Rapid and Highly Sensitive Method for Protein Determination in Biological Samples with m‐Nitrophenylfluorone‐Mo(VI) Complex as a Spectral Probe

Abstract

A simple, rapid, highly sensitive, and selective method for detecting protein in biological samples has been developed, which is based on the interaction between protein and m‐nitrophenylfluorone‐Mo(VI) complex as a spectral probe. The optimum condition for the reaction is investigated. Bovine serum albumin (BSA) obeys Beer's law up to 10 µg · mL^?1, having a molar absorption coefficient of 8.51×10⁶ L · mol^?1 · cm^?1 at 535 nm. Many amino acids and metal ions do not interfere. The results of determination for biological samples are comparable to those obtained by the Bradford method. Meanwhile, the binding number is also determined.     

A HYDROGEN PEROXIDE SENSOR BASED ON PRUSSIAN BLUE AND DNA-MODIFIED ELECTRODE

The polyvinylpyrrolidone (PVP) protected Prussian blue (PB) nanoparticles were prepared for use as a sensor for the catalytic reduction of hydrogen peroxide. The nanoparticles were used to modify a gold electrode, which was applied to detect hydrogen peroxide. Impedance spectra and differential pulse voltammetry were applied to detect the performance of the novel electrode and its response to H₂O₂ and Ramos cell smash fluid. Under the optimized experimental conditions, hydrogen peroxide was detected in a linear range of 6.25 × 10^?7 to 1.0 × 10^?5 mol · L^?1, and the detection limit was 7.12 × 10^?8 mol · L^?1 according to 3σ rule. Under the same conditions, hydrogen peroxide was determined in Ramos cell smash fluid with a linear range from 400–80000 mol mL^?1, with a detection limit of 114 mL^?1 according to 3σ rule. The modified electrode with Prussian blue nanoparticles displayed high sensitivity, good reproducibility, and long-term stability to hydrogen peroxide.     

Characterization and application of lornoxicam,europium(III), and lysozyme fluorescence

A novel and sensitive spectrofluorimetric method was developed for the determination of lornoxicam. The method was based on the fluorescence enhancement of europium(III) by formation of a ternary complex with lornoxicam in the presence of lysozyme as the co-ligand. The fluorescence signal for the lornoxicam-europium (III)-lysozyme system was monitored at an excitation wavelength of 620 nm and an emission wavelength of 390 nm. The parameters affecting the fluorescence intensity were optimized systematically and under these conditions the signal was directly proportional to the concentration of lornoxicam from 9.0 × 10^?5 to 1.0 × 10^?2 µg · mL^?1. The detection limit was 2.7 × 10^?5 µg · mL^?1. The relative standard deviation for thirteen replicate measurements of 1.0 × 10^?3 µg · mL^?1 lornoxicam was 1.8%. This method was employed for the determination of lornoxicam in pharmaceutical formulations and biological fluids. The mechanism of fluorescence for the lornoxicam-europium(III)-lysozyme system was discussed.     

STUDY ON THE INCLUSION INTERACTION BETWEEN SULFOBUTYLETHER-β-CYCLODEXTRIN AND CLOZAPINE BY FLOW INJECTION CHEMILUMINESCENCE

The inclusion interaction of sulfobutylether-β-cyclodextrin with clozapine was studied using flow injection chemiluminescence and molecular docking. By use of a homemade flow injection chemiluminescence model of lg[(I ₀?I _s)/I _s] = lgK + nlg[C _clozapine], the formation constant K, the stoichiometric ratio n, and thermodynamic parameters between sulfobutylether-β-cyclodextrin and clozapine were obtained. Results showed that the inclusion forming process of sulfobutylether-β-cyclodextrin/clozapine with a stoichiometric ratio of 1:1 was spontaneous through hydrophobic interaction. The molecular docking results showed that clozapine entered into the cavity of sulfobutylether-β-cyclodextrin with one hydrogen bond. Based on the good linear relationship of quenching of chemiluminescence intensity versus the logarithm of concentration between 0.07 and 50.0 ng mL^?1, a flow injection chemiluminescence method for clozapine was established for the first time with a detection limit of 0.02 ng mL^?1 (3σ). The proposed method was successfully applied for the determination of clozapine in spiked human urine and serum samples, with recoveries from 92.1–108.2% and relative standard deviations less than 2.7%.     

A GREEN METHOD FOR THE DETERMINATION OF CHROMIUM(VI) AND IRON(III) IN WATER BY SEQUENTIAL INJECTION ANALYSIS AND SPECTROPHOTOMETRIC DETECTION

In this article, an organic-reagent-free method was described for the determination of Cr(VI) and Fe(III) by double-system double-wavelength sequential injection technique with a single sample injection. In this approach, the determination of Cr(VI) was based on the detection of a blue unstable intermediate compound resulting from the reaction of Cr(VI) with hydrogen peroxide, and the determination of Fe(III) was based on the color reaction of Fe(III) with thiocyanate in acidic medium. Sequential injection analysis (SIA) parameters, including spacer solution volume, aspiration order, aspiration volumes, flow rate, acid medium, solution acidity, and reagent concentrations, were optimized. The linear range for the determination was 3.0–60.0 μg mL^?1 for Cr(VI) and 1.0–40.0 μg mL^?1 for Fe(III), respectively. The limit of detection (LOD) was 0.6 μg mL^?1 for Cr(VI) and 0.2 μg mL^?1 for Fe(III), and the limit of quantitation (LOQ) was 2.0 μg mL^?1 for Cr(VI) and 0.67 μg mL^?1 for Fe(III). The total volume of the reagent consumed in each determination was only 0.11 mL. The proposed method was applied to the simultaneous determination of Cr(VI) and Fe(III) in electroplating wastewater and environmental waters. The results were in good agreement with those obtained by atomic absorption spectrometry. The recoveries were in the range of 97.5–101.1%.     

Flow Injection Chemiluminescence Analysis of Diphenhydramine Hydrochloride and Chlorpheniramine Maleate

Abstract

A new chemiluminescence (CL) method, using flow injection, is described for the determination of diphenhydramine hydrochloride and chlorpheniramine maleate. The method is based on the restraining effects on the CL reaction of luminol‐potassium ferricyanide in alkaline solutions. The various experimental parameters affecting the chemiluminescence intensity were studied carefully and incorporated into the procedure. The method allows the determination of 1.0–100 µg mL^?1 diphenhydramine hydrochloride and 0.1–10.0 µg mL^?1 chlorpheniramine maleate. The detection limits of the method are 0.3 µg mL^?1 for diphenhydramine hydrochloride and 0.02 µg mL^?1 for chlorpheniramine maleate. The method was successfully applied to the determination of diphenhydramine hydrochloride and chlorpheniramine maleate in pharmaceutical preparations.     

CERIUM(IV)-BASED CHEMILUMINESCENCE OF FELODIPINE SENSITIZED BY RHODAMINE 6G

A simple, rapid, and sensitive flow injection chemiluminescence (FI-CL) method was proposed for the determination of felodipine. The method was based on the CL-emitting reaction between the studied drug and cerium(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine 6G used as a sensitizer. Under the optimum conditions, the proposed procedure had a linear range between 5.0 × 10^?9 and 7.0 × 10^?6 g mL^?1, with a detection limit of 2.0 × 10^?9 g mL^?1. The relative standard deviation was 2.3% for 1.0 × 10^?7 g mL^?1 felodipine solution (n = 11). It was applied to the determination of felodipine in pharmaceutical preparations and biological fluids with satisfactory results. The possible mechanism of the chemiluminescence reaction was also discussed briefly.     

ON-LINE MINI-COLUMN SOLID-PHASE EXTRACTION COUPLED WITH SEQUENTIAL INJECTION FOR THE DETERMINATION OF CADMIUM IN ENVIRONMENTAL SAMPLES

□Trace cadmium(II) in environmental samples was separated and enriched in an automated fashion using a diphenylcarbazone-functionalized silica gel mini-column coupling with sequential injection. Cadmium was determined using a multicomponent system involving the analyte, potassium iodide, ethyl violet, and polyvinyl alcohol. Under the optimum conditions, the linear range for cadmium(II) was 0.015–0.50 µ g mL^?1, and the detection limit was 0.012 µ g mL^?1. The relative standard deviation of 11 determinations for 0.1 and 0.2 µ g mL^?1 standard solutions was smaller than 3.5%. This method was applied for the determination of cadmium(II) in water, plant, soil, and electroplating wastewater. No statistically significant differences in the results were observed between the reported method and those obtained by atomic absorption spectrometry. The analysis was performed within 13 min and a total reagent volume of only 0.14 mL (0.07 mL of eluent and 0.07 mL of reagents) was consumed in each determination of cadmium(II).     

Determination of R‐Deprenyl using a Maltodextrin‐Based Enantioselective,Potentiometric Membrane Electrode

Abstract

The enantioselective, potentiometric membrane electrode (EPME) based on maltodextrin with dextrose equivalence (DE) 16.5–19.5 is proposed for the assay of R‐deprenyl. The linear concentration range for the proposed electrode is 10^?10?10^?3 mol L^?1. The slope of the electrode is 53.1 mV per decade of concentration. The detection limit is 3.6×10^?11 mol L^?1. The proposed electrode could be reliably employed for the assay of R‐deprenyl raw material and its pharmaceutical formulation, Lentogesic tablets.     

Electrochemical Behavior of Uric Acid at a Meso‐2,3‐Dimercaptosuccinic Acid Self‐Assembled Gold Electrode

Abstract

The fabrication and electrochemical characteristics of a meso‐2,3‐dimercaptosuccinic acid (DMSA) self‐assembled monolayer modified gold electrode were investigated. The DMSA self‐assembled electrode can enhance the electrochemical stability of uric acid (UA) and the electrochemical reaction of UA on the DMSA electrode has been studied by cyclic voltammetry and electrochemical quartz crystal microbalance. Some electrochemical parameters, such as diffusion coefficient, standard rate constant, electron transfer coefficient, and protons transfer number have been determined for the electrochemical behavior on the DMSA self‐assembled monolayer electrode. The electrode reaction of UA is an irreversible process which is controlled by the diffusion of UA with two electrons and two protons transfer at the DMSA/Au electrode. In phosphate buffer (pH 5.0), the peak current is proportional to the concentration of UA in the range of 8.0×10^?5?1.0×10^?2 mol L^?1 and 8.0×10^?5?8.0×10^?3 mol L^?1 for the cyclic voltammetry and differential pulse voltammetry methods with the detection limits of 1×10^?6 and 8×10^?7 mol L^?1, respectively. This method can be applied to the determination of the UA concentration.     

Inductively Coupled Plasma Optical Emission Spectrometric Determination of Gadolinium in Urine Using Flow Injection On‐Line Sorption Preconcentration in a Knotted Reactor

Abstract

An on‐line gadolinium preconcentration and determination system, implemented with ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry (ICP‐OES), associated with flow injection (FI) was studied. Gadolinium was retained as Gd‐2‐(5‐bromo‐2‐pyridilazo)‐5‐diethylaminophenol complex (Gd‐5‐Br‐PADAP) at pH 9.0, on the inner walls of the knotted reactor (KR). The collected analyte complexes were quantitatively eluted from the 200 cm KR with 30% (v/v) nitric acid. An enhancement factor of 255‐fold was obtained (17 for KR and 15 for USN). The detection limit (DL) value for the preconcentration of 15 mL of sample was 4.0 ng L^?1. The relative standard deviation (RSD) was 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for gadolinium was linear, with a correlation coefficient of 0.9996 at levels near the detection limit up to at least 200 µg L^?1. The method was successfully applied to the determination of gadolinium in urine samples.     

On‐Line Preconcentration System for Cobalt Determination in Bee Honey Using Flow Injection‐Flame AAS

Abstract

A methodology for the on‐line preconcentration and determination of cobalt by flame atomic absorption spectrometry (FAAS) coupled with flow injection (FI) in bee honey samples is proposed. For the retention of cobalt, 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol (5‐Br‐PADAP) complexing reagent, and Amberlite XAD‐7 resin were used, at pH 9.5. The Co‐(5‐Br‐PADAP) complexes were completely removed from the column with ethanol. An enrichment factor (EF) of 50‐fold for a sample volume of 50 mL was obtained. The detection limit (DL) for the preconcentration of 50 mL of aqueous solution was 0.18 µg L^?1. The precision for 10 replicate determinations at the 10 µg L^?1 cobalt levels was 3.6% relative standard deviation (RSD), calculated with peak heights obtained. The calibration graph using the preconcentration system for cobalt was linear with a correlation coefficient of 0.9997 at levels near the DL, up to at least 300 µg L^?1. The method was successfully applied to determination of total cobalt in honey samples.     

Determination of Lead in Spiked Seawater Samples by Electrothermal Atomic Absorption Spectrometry using Chemical Modifiers

Abstract

The determination of lead in spiked sodium chloride solution with 3.4% salinity and natural sea‐water samples by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman‐effect background correction was investigated using neodymium, samarium, and erbium salts as modifiers with the addition of citric acid (CA) as a reducing agent. In order to demonstrate the high potential of rare earth metals in combination with citric acid, optimum pyrolysis temperature, atomization temperature, and optimum masses of neodymium, samarium, and erbium were found for the determination of lead. These modifiers were used for the determination of lead in sodium chloride solution with 3.4% salinity and in natural sea water samples by means of the calibration graphs prepared with pure analyte solutions.

The detection limits for lead spiked sample matrices were calculated with the 2σ criterion between 2.0 to 2.1 ng mL^?1 for neodymium and citric acid, between 5.3 to 7.4 ng mL^?1 for samarium and citric acid, and between 1.7 to 2.1 ng mL^?1 for erbium and citric acid and for a sample volume of 10 µL. The recoveries for lead spiked sea water samples were 97–102%, with neodymium and citric acid modifier and erbium and citric acid modifier. They were only 66–68% without modifier.     

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY AND GAS CHROMATOGRAPHY — MASS SPECTROMETRY METHODS FOR THE DETERMINATION OF IMIDACLOPRID,CHLORPYRIFOS, AND BIFENTHRIN RESIDUES IN TEA LEAVES

□ A sensitive, rapid, and reproducible high-performance liquid chromatography–diode array method and a gas chromatography/mass spectrometry method were developed to determine imidacloprid, chlorpyrifos, and bifenthrin in tea leaves. Solid-phase extraction (SPE) was employed for sample preparation. The extraction solvent used was acetonitrile:toluene (3:1, v/v). Linearity was observed in tea spiked with 0.4–6.0 µ g mL^?1 (n = 6) of imidacloprid, 0.8–15.0 µ g mL^?1 (n = 6) of chlorpyrifos, and 0.3–6.6 µ g mL^?1 (n = 6) for bifenthrin. The correlation coefficients obtained were higher than 0.99 for all pesticides. The limits of detection for imidacloprid, chlorpyrifos, and bifenthrin were 0.06, 0.12, and 0.05 mg kg^?1, respectively. The limits of quantification for imidacloprid, chlorpyrifos, and bifenthrin were 0.20, 0.40, and 0.17 mg kg^?1, respectively. Recoveries of the analytes were between 80% and 96% with RSDs <10% (intra-day and inter-day). The methods were applied to monitor pesticide residues in tea. The results obtained by both techniques indicated that their feasibility for practical applications.     

DESIGN OF A SENSITIVE MEMBRANE OPTODE FOR IRON DETERMINATION

An optical chemical sensor has been developed for the sensitive determination of Fe (III) ions by spectrophotometry. The optical membrane was constructed by immobilization of methyltrioctylammonium chloride on triacetylcellulose polymer. The exchange of thiocyanate as counter ion in the membrane sensitized this film to Fe (III). The sensing membrane is capable of determining Fe(III) reversibly over a dynamic range of 7.11 × 10^?7?8.88 × 10^?5 mol L^?1 with a limit of detection of 6.02 × 10^?7 mol L^?1 and a response time of 5 min. This optode can easily be regenerated by 0.1 mol L^?1 of sodium fluoride solution. The relative standard deviation for eight replicate measurements of 7.11 × 10^?6 and 5.33 × 10^?5 mol L^?1 of Fe (III) was 4.2 and 3.7%, respectively. The sensor was successfully applied for the determination of iron in tablet and water samples.     

Determination of baicalin in cosmetics and toothpaste by solid-phase extraction and high-performance liquid chromatography

Baicalin was determined in cosmetics and toothpaste by high-performance liquid chromatography. The samples were extracted with ultrasound in 75% ethanol for 20 min, purified by anion exchange solid-phase extraction cartridge, and the components were separated on a C18 column. The limits of detection and quantification were 3.0 mg kg^?1 and 10.0 mg kg^?1. The recovery was from 81.3–101.6%. A linear relationship was present from 1.00–100 µg · mL^?1 of baicalin. The protocol was simple, sensitive, selective, and used to determine baicalin in personal care products. Baicalin was not present in materials contrary to the labeled contents.     

Comparison of some physical techniques for detection of spoilage in apple juice inoculated with Saccharomyces cerevisiae: Optical and photothermal methods

Abstract

Several physical techniques were used to study the extent of spoilage in apple juice deliberately inoculated with yeast (concentration of Saccharomyces cerevisiae ranged from 25 cells mL^?1 to 2.5 × 10⁶ cells mL^?1, respectively) and their performance compared in terms of detection limit achieved. The optical methods used in this investigation rely on the measurement of either absorption [as is the case for classical spectrophotometry (SP) and the so called optothermal window (OW), a variant of a photothermal method], or scattering [examples are turbidimetry (TB), laser scattering (SC), and laser speckle fluctuation (SF)]. It is shown that the presence of yeast increases both optical absorption and scattering. The most favorable detection limit (25 cells mL^?1) and a highest (nearly 10⁴) dynamic range, combined with a good linearity, were obtained with the experimental set‐up for SC. In addition, the extent of correlation between different methods was determined using two markedly different reference substances, i.e., (i) the mixture of apple and blackcurrant juices, representing a strongly absorbing sample, and (ii) diluted (dilution factor of 10³) milk as a strong scatterer. Finally, one has monitored the progress of a spontaneous spoilage process in the inoculated juices stored at 5°C under aerobic conditions.     

Determination of Myricetin in Medicinal Plants by High-Performance Liquid Chromatography

The concentrations of myricetin in medicinal plants such as Rosa canina L. (rosa hip), Terebinthina chica L. (terebinth), Urtica dioica L. (nettle), and Portuca oleracea L. (purslane) were determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS). The aglycones of myricetin were extracted using methanol–ascorbic acid– hydrochloric acid, methanol–hydrochloric acid, and methanol, separated within 5 min, and individually quantitated in the positive ionization mode using optimized conditions for HPLC-MS. Methanol–ascorbic acid–hydrochloric acid was the optimum extraction solvent. The myricetin concentration in the plants were between 3 and 58 mg kg^?1, with a limit of quantification equal to 0.1 mg L^?1.     

A Chitosan-Graphene Electrochemical Sensor for the Determination of Copper(II)

Graphite oxide was prepared by oxidizing graphite powder, reduced to graphene using hydrazine hydrate, and the grapheme was mixed with chitosan to form a composite that was used to modify a glassy carbon electrode for the determination of copper(II). The electrochemical behavior of the modified electrode was studied by cyclic and square wave voltammetries. The morphology and structure of the composite were characterized by infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy. In addition, the proportion of composite material, pH, and adsorption time was optimized. Under the optimized experimental conditions, the sensor showed a linear dynamic range from 1.0 × 10^?9 to 1.5 × 10^?8 mol · L^?1 for copper(II) with a limit of detection of 4.3 × 10^?10 mol · L^?1 at a signal-to-noise ratio of three. The sensor displayed excellent electrochemical response and high sensitivity.     

Determination of dopamine using the fluorescence quenching of 2, 3-diaminophenazine

A facile and sensitive fluorescent strategy for the determination of dopamine is reported using 2, 3-diaminophenazine. Dopamine caused autooxidation in the presence of oxygen with catalysis by Mn²⁺ and formed 2, 3-dihydro-1H-indole-5,6-dione. 2, 3-Diaminophenazine provided relatively strong fluorescence. 2, 3-Diaminophenazine in aqueous solution caused fluorescence quenching when the aminochrome condensed with 2, 3-diaminophenazine to allow the determination of dopamine. Under the optimized conditions, the linear dynamic range for dopamine was from 2.0 × 10^?6 mol · L^?1 to 6.1 × 10^?5 mol · L^?1 with a detection limit of 1.76 × 10^?6 mol · L^?1.