Simultaneous Analysis of Sugars and Polyphenols in Tobacco by CZE with Amperometric Detection Based on a Cu2O/MWCNT-COOH Composite Electrode

A composite electrode was fabricated from Cu₂O powder, carboxyl-functionalized multi-wall carbon nanotubes (MWCNT-COOH), and paraffin oil in the proportions 51:17:32 (w/w). This composite electrode was used for amperometric detection (CZE–AD) in simultaneous capillary zone electrophoretic analysis of chlorogenic acid, rutin, sucrose, glucose, mannose, and fructose in tobacco samples. Under the optimum conditions, the six analytes could be separated in 100 mmol L^?1 NaOH buffer within 30 min. Good linearity was achieved in the range 1 × 10^?7–1 × 10^?4 mol L^?1 for the two polyphenols and 5 × 10^?6–1 × 10^?3 mol L^?1 for the four sugars. The detection limits (S/N = 3) for the polyphenols and sugars were as low as 10^?8 mol L^?1 and 10^?6 mol L^?1, respectively.     

Spectrophotometric Determination of Furosemide Based on Its Complexation with Fe(III) in Ethanolic Medium Using a Flow Injection Procedure

Abstract

A fast flow injection procedure with spectrophotometric detection based on the furosemide complexation with Fe(III) ions in ethanolic media is described. As carrier the flow single line system configuration used an ethanolic 10^?2 mol L^?1 Fe(III) solution flowing at 1.0 mL min^?1, a 50 cm sample loop (250 µL total sample injection), and a 50 cm long reactor coil, at room temperature. The detection at 513 nm presented a linear dynamic range from 1.00×10^?4 to 1.00×10^?2 mol L^?1, obeying the linear equation Abs=8.9×10^?3+22.3×[furosemide] (r=0.998, n=7). The limit of detection (3σ/slope) was 3.00×10^?5 mol L^?1. The proposed method was applied to four commercial samples from different suppliers, as tablets and ampoules, and a synthetic urine sample spiked with the analyte without an effect from the other substances present in the formulation. The proposed procedure presented an analytical frequency of 95 measurements per hour. The results agreed with those from both the label and those determined by a spectrophotometric comparative procedure. Recoveries close to 100% were found in the commercial formulations and synthetic urine matrixes.     

Molecular imprinting polymer electrosensor based on gold nanoparticles for theophylline recognition and determination

An electrochemical sensor for theophylline (ThPh) was prepared by electropolymerizing o-phenylenediamine on a glassy carbon electrode in the presence of ThPh via cyclic voltammetry, followed by deposition of gold nanoparticles using a potentiostatic method. The effects of pH, ratio between template molecule and monomer, number of cycles for electropolymerization, and of the solution for extraction were optimized. The current of the electro-active model system hexacyanoferrate(III) and hexacyanoferrate(IV) decreased linearly with successive addition of ThPh in the concentration range between 4.0?×?10^?7?~?1.5?×?10^?5 mol·L^?1 and 2.4?×?10^?4?~?3.4?×?10^?3 mol·L^?1, with a detection limit of 1.0?×?10^?7 mol·L^?1. The sensor has an excellent recognition capability for ThPh compared to structurally related molecules, can be regenerated and is stable.

Flow‐Injection Spectrophotometric Determination of N‐acetylcysteine in Pharmaceutical Formulations with On‐Line Solid‐Phase Reactor Containing Zn(II) Phosphate Immobilized in a Polyester Resin

Abstract

A flow‐injection spectrophotometric procedure was developed for determining N‐acetylcysteine in pharmaceutical formulations. The sample was dissolved in deionized water and 400 µl of the solution was injected into a carrier stream of 1.0×10^?2 mol l^?1 sodium borate solution. The sample flowed through a column (70 mm length×2.0 mm i.d.) packed with Zn₃(PO₄)₂ immobilized in a polymeric matrix of polyester resin and Zn(II) ions were released from the solid‐phase reactor because of the formation of the Zn(II) (N‐acetylcysteine)₂ complex. The mixture merged with a stream of borate buffer solution (pH 9.0) containing 5.0×10^?4 mol l^?1 Alizarin red S and the Zn(II)Alizarin red complex formed was measured spectrophotometrically at 540 nm. The analytical curve was linear in the N‐acetylcysteine concentration range from 3.0×10^?5 to 1.5×10^?4 mol l^?1 (4.9 to 24.5 µg ml^?1) with a detections limit of 8.0×10^?6 mol l^?1 (1.3 µg ml^?1). The relative standard deviations (RSDs) were smaller than 0.5% (n=10) for solutions containing 5.0×10^?5 mol l^?1 (8.0 µg ml^?1) and 8.0×10^?5 mol l^?1 (13.0 µg ml^?1) of N‐acetylcysteine, and the analytical frequency was 60 determinations per hour. A paired t‐test showed that all results obtained for N‐acetylcysteine in commercial formulations using the proposed flow‐injection procedure and a comparative procedure agreed at the 95% confidence level.     

Static and Hydrodynamic Monitoring of Citalopram Based on its Electro-oxidation Behavior at a Glassy-Carbon Surface

Abstract

The electrooxidative behavior of citalopram (CTL) in aqueous media was studied by cyclic voltammetry (CV) and square-wave voltammetry (SWV) at a glassy-carbon electrode. The electrochemical behaviour of CTL involves two electrons and two protons in the irreversible and diffusion controlled oxidation of the tertiary amine group. The maximum analytical signal was obtained in a phosphate buffer (pH = 8.2). For analytical purposes, an SWV method and a flow-injection analysis (FIA) system with amperometric detection were developed. The optimised SWV method showed a linear range between 1.10 × 10^?5–1.20 × 10^?4 mol L^?1, with a limit of detection (LOD) of 9.5 × 10^?6 mol L^?1. Using the FIA method, a linear range between 2.00 × 10^?6–9.00 × 10^?5 mol L^?1 and an LOD of 1.9 × 10^?6 mol L^?1 were obtained. The validation of both methods revealed good performance characteristics confirming applicability for the quantification of CTL in several pharmaceutical products.     

Determination of Polyethylene Glycol Monoester Acrylate and Polyethylene Glycol Diester Acrylate Using Reversed-Phase High-Performance Liquid Chromatography

A procedure was developed for the determination of polyethylene glycol monoester acrylate (PEGMA) and polyethylene glycol diester acrylate (PEGDA) by reversed-phase high performance liquid chromatographic (RP-HPLC) with UV detector. Sample was well separated on an SinoChrom ODS-BP (C-18) column (200 × 4.6 mm i.d., 5 μm) with mobile phases composed of acetonitrile-phosphate buffer solution (0.05 mol · L^?1 pH = 6.86) in the ratio of 42:58 (v/v). The PEGMA and PEGDA were detected by UV detector at 205 nm, and quantitatively analyzed with an external standard of methyl acrylate. For PEGMA, the linear response ranged from 0.40 × 10^?5 mol · L^?1 to 2.00 × 10^?3mol · L^?1 (r² > 0.999), the detection limit was 0.12 × 10^?5 mol · L^?1, the recovery rate was found to be 93.4%–99.7%. For PEGDA, the linear response ranged from 0.20 × 10^?5 mol · L^?1 to 1.00 × 10^?3mol · L^?1 (r² > 0.999), the detection limit was 0.04 × 10^?5 mol · L^?1, the recovery rate was found to be 99.1% ～ 105.8%. This quantitative method can also be used in the HPLC analysis of other α,β-unsaturated esters.     

4-Hydroxy-3,5-pyridinedicarboxylic Acids: Synthesis,Complexation Properties Towards Fe(III), Al(III), Cu(II), Zn(II), Human Serum Albumin,and Cellular Toxicity

4-hydroxy-3,5-pyridinedicarboxylic acid (DQ58) and 4-hydroxy-1-methyl-3,5-pyridinedicarboxylic acid (DQ71508) have been synthesized, and their Fe(III), Al(III), Cu(II), and Zn(II) coordination properties have been studied by potentiometry, UV–Vis spectroscopy (in the case of Fe(III), Al(III), Cu(II)), ¹H-NMR (for Al(III)) and EPR (for Cu(II)). The thermodynamic results were used to model the extent of the toxic metal ions decorporation (Fe(III) or Al(III)) in the presence of the essential metal ions (Cu(II) or Zn(II)). DQ58 and DQ71508 were demonstrated to interact with human serum albumin (HSA), which is assumed to be the main serum transporter of the chelators, and binding constants have been obtained by ultrafiltration. IC₅₀ values of 5.185 × 10^?3 and 1.033 × 10^?3 mol·L^?1 were collected after 24 and 48 h of treatment with DQ71508 towards human embryonic kidney HEK-293 cells, demonstrating the relatively low cytotoxicity of this compound. According to these results, both DQ58 and DQ71508 seem to be potential candidates for Fe chelation therapy, and DQ58 is a better Fe(III) chelator than DQ71508.     

Highly Sensitive Flow-Injection Chemiluminescence Detection of Carbonyl Compounds in Wine Samples

A modified Trautz–Schorigin reaction, by using tannic acid-H₂O₂ system for the oxidation and determination of two kinds of carbonyl compounds was developed in this paper. It was found that formaldehyde and acetaldehyde could effectively enhance the chemiluminescence signals of tannic acid–H₂O₂ system in alkaline medium. Under optimized conditions, the proposed method has a linear range of 7 × 10^?9–1 × 10^?4 mol L^?1 for formaldehyde and 1 × 10^?8–1 × 10^?4 mol L^?1 for acetaldehyde with detection limits of 9 × 10^?11 and 3 × 10^?10 mol L^?1, respectively. The relative standard deviations for 15 repeated measurements of 1 × 10^?6 mol L^?1 HCHO and CH₃CHO are 1.13% and 1.65%, respectively. Analysis time per sample is 35 seconds. A comparison of results found by the proposed method with those obtained by a standard reference method provided good agreement. The proposed method is simple, rapid, convenient, and sensitive.     

Plutonium oxidation state distribution in natural clay and goethite

Distribution of Pu(IV) and Pu(V) oxidation states at trace initial concentrations (10^?10–10^?11 mol L^?1) was studied in a liquid- and solid-phase of natural clay and goethite systems. Experiments showed an increase in the concentration of Pu(III) up to 11% at pH 5 in solids of the natural clay ?0.1 mol L^?1 NaNO₃ system containing Pu(IV) after 7-day contact. A kinetic sorption/reduction experiment with goethite suspensions (0.01 mol L^?1 NaNO₃ containing Pu(V)) indicated the presence of Pu(III) in the solids up to 15%.     

Carbon ceramic electrodes modified with mixed oxides SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> for determination of levofloxacin

The preparation of a carbon ceramic electrode modified with SnO₂ (CCE/SnO₂) using tin dibutyl diacetate as precursor was optimized by a 2³ factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO₂ provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO₂, indicating that SnO₂ when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10^?5 to 6.97×10^?4 mol L^?1 with quantification and detection limits of 3.80×10^?5 mol L^?1 (14.07 mg L^?1) and 1.13×10^?5 mol L^?1 (4.18 mg L^?1), respectively.     

Fabrication of a new nanocomposite modified carbon paste Al<Superscript>3+</Superscript>-ion selective electrode based on <Emphasis Type="Italic">N,N</Emphasis>′-dipyridoxyl (1,2-cyclohexanediamine) (PYCA) as an active material

Construction and feature of a nanocomposite modified carbon paste electrode for aluminum(III) ion determination based on N,N′-dipyridoxyl (1,2-cyclohexanediamine) (PYCA) as a novel selector material will be covered by this paper. The optimum composition, Nernstian slope/linear range/detection limit in the forms of calibration graph, response time, utilizable pH range, repeatability and precision of measurements of the aluminum(III) ion using the new fabricated Al³⁺-CPE was evaluated. The optimal composition which performed over Al⁺³ ion concentration range 1.0 × 10^?8 mol L^?1–1.0 × 10^?1 mol L^?1 with near-Nernstian slope equal 20.9 ± 0.2 mV decade^?1 and low detection limit about 5.0 × 10^?9 mol L^?1, was formed of ionophore (PYCA 3 %), binder (paraffin oil 30 %), modifier [multi-wall carbon nanotubes (MWCNTs) 1 %] & [Nanosilica (NS) 0.5 %], and inert matrix (graphite powder 65.5). The request time to give rise Nernstian response of electrode for concentrations from 1.0 × 10^?8 mol L^?1 to 1.0 × 10^?1 mol L^?1 of Al³⁺ ion solution was estimated about ~6 s. The new Al³⁺-CPE was applied in pH range 2.0–5.0 with no consequential change in potential response. To verify the selectivity of electrode toward aluminum(III) ion in the presence of different metallic cations, matched potential method was used. The obtain results in analytical applications reflect the excellent ability of this electrode to play the role as endpoint indicator electrode in both titration and direct potentiometric measurements.     

RP-LC Determination of Residual Monomers in Polycarboxylate Superplasticizers

A procedure was developed for the determination of residual monomers in polycarboxylate superplasticizer by reversed-phase high performance liquid chromatography. Seven kinds of residual monomers were quantitatively determined on a SinoChrom ODS-BP (C18) column and UV detector at 205 nm. The mobile phases which were used to determine micromolecular monomers were composed of acetonitrile and phosphate buffer solution (0.05 mol L^?1, pH = 3) in the ratio of 8:92 (v/v). While the mobile phases for long side-chain monomers testing were composed of acetonitrile and phosphate buffer solution (0.05 mol L^?1, pH = 6.5) in the ratio of 40:60 (v/v). The linear response ranged from 4.0 × 10^?6?C2.0 × 10^?3 mol L^?1. The detection limit was 0.12 × 10^?5?C0.8 × 10^?5 mol L^?1. Determination of real samples showed that relative standard deviation of high conversion rate samples was 3.1?C8.7% and standard addition recovery ratio was 91.5?C102.8%. While the relative standard deviation of low conversion rate samples was less than or close to 1% and the standard addition recovery ratio was 96.3?C103.1%.     

A Flow Injection Chemiluminescence Method for the Determination of Protein Using Copper(II)-Alizarin Red S Complex as an Efficient Chemiluminescent Probe

A sensitive flow injection chemiluminescence (CL) method is proposed for the determination of bovine serum albumin (BSA) using Copper(II)-Alizarin Red S (ARS) complex as an efficient chemiluminescent probe. The detection is based on the binding of the copper(II)-ARS complex to proteins and the catalytic activity of copper(II)-ARS in the luminol-H₂O₂ CL system. Under the selected conditions, the CL intensity is linear with the concentration of BSA in the range of 5.0 × 10^?11 to 1.0 × 10^?9 mol · L^?1. The detection limit was 2.0 × 10^?11 mol · L^?1. The method is successfully applied to the determination of protein in urine.     

A Multicommuted Flow‐based System for Hydrogen Peroxide Determination by Chemiluminescence Detection Using a Photodiode

Abstract

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III).

The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l^?1 H₂O₂ with a LD of 1.8 µmol l^?1 H₂O₂ and coefficient of variations smaller than 0.8% for 1.0×10^?5 mol l^?1 and 6.8×10^?5 mol l^?1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.     

银（III）配合物-鲁米诺流动注射化学发光新体系测定肾上腺素

儿茶酚胺是一类非常重要的神经递质,在人体的心血管系统、神经系统、内分泌腺、肾脏、平滑肌等组织系统的生理活动中起着广泛的调节作用。肾上腺素为儿茶酚胺的一种,建立灵敏、高效的肾上腺素检测技术具有重要的临床意义。本文将银（Ⅲ）配合物与鲁米诺组成新的流动注射化学发光体系,利用碱性介质中肾上腺素对三价银配合物－鲁米诺化学发光体系有明显的增强效应来测定肾上腺素的含量,并据此建立了高效测定肾上腺素的流动注射化学发光新方法。在优化的条件下,该方法测定肾上腺素的线型范围为1.0×10－9～1.0×10－7 mol L-1,检出限为8.0×10－10 mol L-1,对1.5×10－8 mol L-1肾上腺素11次平行测定,其相对标偏差为2.9％。利用建立的分析方法测定了药物肾上腺素,并对三价银－鲁米诺化学发光新体系测定肾上腺素的反应机理进行了讨论。     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Determination of Catechol by a Laccase Biosensor Based on Silica-Modified Zirconia Nanoparticles

A promising nanotechnological material, zirconia nanoparticles modified with SiO₂, was used as a medium for the immobilization of laccase to construct a novel biosensor that exhibits sensitive amperometric response to catechol in 0.1 mol · L^?1 phosphate buffer (pH 6.0) using cyclic voltammetry. The linear response to catechol was from 1.0 × 10^?6 to 1.0 × 10^?4 mol · L^?1 and the detection limit was 3.5 × 10^?7 mol · L^?1 at a signal-to-noise ratio of 3. The biosensor exhibited good stability, precision, and few interferences.     

Determination of Hydrogen Peroxide Using a Novel Sensor Based on Fe3O4 Magnetic Nanoparticles

Fe₃O₄ magnetic nanoparticles were synthesized by chemical co-precipitation with sodium citrate as a surfactant and were used with chitosan to construct a novel hydrogen peroxide sensor. The electrochemical behavior of hydrogen peroxide at the sensor was investigated by cyclic voltammetry. The composite film electrocatalyzed the reduction of hydrogen peroxide, and the peak current increased linearly with concentration from 1.00 × 10^?5 to 1.00 × 10^?3 mol · L^?1 (R = 0.9974) with a detection limit of 1.53 × 10^?6 mol · L^?1. This novel nonenzyme sensor provided good sensitivity, stability, and precision with potential applications.     

Voltammetric determination of 17α-ethinylestradiol hormone in supply dam using BDD electrode

In this work, a simple method for electroanalytical determination of 17α-ethinylestradiol (EE2) hormone in natural waters was developed using a boron-doped diamond electrode (BDD). The analyses were performed using square wave voltammetry and the parameters were optimized. The results showed a well-defined irreversible oxidation peak (BR buffer 0.1 mol L^?1, pH 8.0) at +0.65 V (vs. Ag/AgCl). The voltammetric results showed also that the oxidation process is controlled by adsorption of species and indicated that there are two electrons involved. The obtained analytical curves for 17α-ethinylestradiol presented good linearity in the concentration range 9.9?×?10^?7 to 5.2?×?10^?6 mol L^?1 in utlrapure water and 7.9?×?10^?7 to 5.2?×?10^?6 mol L^?1 in natural water samples (supply dam). Detection limits (DL) obtained were between 2.4?×?10^?7 and 7.5?×?10^?7 mol L^?1 and quantification limits (QL) between 7.9?×?10^?7 and 2.5?×?10^?6 mol L^?1. The recovery experiments showed values between 86 and 114 % for spiked samples thus indicating the applicability of the electroanalytical methodology to quantify 17α-ethinylestradiol directly in natural water of supply Dam (Billings Dam in Diadema-SP. Brazil), without any preconcentration or derivatization.     

Solid Phase Extraction and High Performance Liquid Chromatography for Determination of Glyoxylic Acid in a Selective Oxidation Reaction

Currently, the development of a new method for the analysis of glyoxylic acid in selective oxidation of glyoxal system has become a key subject in its new industrial process development. Since solid phase extraction (SPE) could isolate and concentrate desired analytes from complex matrices, in this paper we tested the possibility of coupling SPE technique with HPLC for simultaneous determination of glyoxylic acid, formic acid, and oxalic acid in this complex chemical reaction system. Results demonstrated that the developed method could be successfully applied to this system, after samples were passed through SAX cartridges and yielded recoveries from 96.7% to 103%. The limits of detection were 2.6 × 10^?6, 3.6 × 10^?6, and 3.5 × 10^?7 mol L^?1, respectively; and their linear ranges between 1 × 10^?6 and 1 × 10^?2 mol L^?1.