Spectrophotometric and spectrofluorimetric determination of iodide by extraction of ICl−2 with rhodamine B

Iodide is determined after oxidation with nitrous acid in 5 M hydrochloric acid to ICl^?₂. The ion-pair formed with rhodamine B is extracted into toluene and measured spectrophotometrically (0.5–5 × 10^?5 M) or spectrofluorimetrically (1–10 × 10^?6 M). The relative standard deviations were 1.8% for the determination of 5 × 10^?6 M iodide (n = 5) by spectrofluorimetry and 2.3% (n = 50) for 1 × 10^?5 M iodide by spectrophotometry. Periodate, iodate and iodine responded exactly as iodide.     

A study of sodium bis(2-ethylhexyl) sulfosuccinate adsorption on silica from silver and gold organosols

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT) and silver and gold nanoparticles on SiO₂ from heptane solutions has been investigated by spectophotometery and CHN analysis. The adsorption isotherm of Aerosol OT is described by the Langmuir equation. Sorption capacity (2.4 × 10^–4 mol/g), sorption constant (9.0 m³/mol), and area per Aerosol OT molecule in an adsorption layer (0.83 nm²) have been determined. It has been shown that, at Aerosol OT concentrations lower than 6 × 10^–4 M, gold and silver ((0.3–6) × 10^–4 M) are simultaneously extracted by 98%; however, they have no effect on the adsorption and determination of the surfactant.     

Simultaneous Square‐Wave Voltammetric Determination of Paracetamol,Caffeine and Orphenadrine in Pharmaceutical Formulations Using a Cathodically Pretreated Boron‐Doped Diamond Electrode

An electroanalytical method for the simultaneous determination of paracetamol (PAR), caffeine (CAF), and orphenadrine (ORPH) using the square‐wave voltammetry (SWV) and a cathodically pretreated boron‐doped diamond electrode was developed. The method exhibits linear responses to PAR, CAF, and ORPH in the concentration ranges 5.4×10^?7–6.1×10^?5 M, 7.8×10^?7–3.5×10^?5 M, and 7.8×10^?7–3.5×10^?5 M, respectively, with detection limits of 2.3×10^?7 M, 9.6×10^?8 M, and 8.4×10^?8 M, respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in pharmaceutical formulations.     

Electrochemical investigation and determination of ceftazidime in pharmaceutical dosage forms and human urine

A voltammetric study of the oxidation of Ceftazidime (CEFT) has been carried out at the glassy carbon electrode by cyclic, differential pulse (DPV) and square wave (SWV) voltammetry. The oxidation of CEFT was irreversible and exhibited diffusion controlled process depending on pH. The oxidation mechanism was proposed and discussed. According to the linear relationship between the peak current and concentration, DPV and SWV voltammetric methods for CEFT assay in pharmaceutical dosage forms and human urine were developed. For analytical purposes, a well resolved diffusion controlled voltammetric peak was obtained in 0.1 M H₂SO₄ at 1.00 and 1.02 V for differential pulse and square wave voltammetric techniques, respectively. The linear response was obtained within the range of 4 × 10^?6?8 × 10^?5 M with a detection limit of 6 × 10^?7 M for differential pulse and 4 × 10^?6–2 × 10^?4 M with a detection limit of 1 × 10^?6 M for square wave voltammetric technique. The determination of CEFT in 0.1 M H₂SO₄ was possible over the 2 × 10^?6–1 × 10^?4 M range in urine sample for both techniques. The standard addition method was used for the recovery studies.     

Artificial Enzyme Mimics for Catalysis and Double Natural Enzyme Co-immobilization

This work presents a new chemiluminescent (CL) probe array assay. The new type CL probe array is based on enzyme mimics of Co₃O₄–SiO₂ mesoporous nanocomposite material, which not only have an excellent catalytic effect on the luminol–H₂O₂ CL reaction in an alkaline medium but also can be used for the immobilization of enzymes. The linear range of the lactose concentration is 3.0?×?10^?7 to 1.0?×?10^?5 g mL^?1 and the detection limit is 6.9?×?10^?8 g mL^?1. β-Galactosidase and glucose oxidase were selected as a model for enzyme assays to demonstrate the applicability of Co₃O₄–SiO₂ mesoporous nanocomposite material in multienzyme immobilization. The novel bifunctional CL probe array has been successfully applied to the determination of lactose in milk.     

Periodate oxidation analysis of carbohydrates : Part I. Spectrophotometr1c determination of glyoxal in dialdehyde fragments formed from glycosides with 2,4-dinitrophenylhydrazine

A simple procedure for the determination of glyoxal in dialdehyde fragments, formed from glycosides by periodate oxidation, is proposed. By heating sample solutions prepared by dilution of reaction mixtures for periodate oxidation, with an aqueous dimethylsulfoxide solution of 2,4-dinitrophenylhydrazine hydrochloride. followed by addition of an aqueous ethanolic solution of potassium hydroxide, intense color with an absorption maximum at 576 nm developed. The spectrophotoinetric method based on this color reaction makes it possible to determine selectively 1·10^?2–2·10^?1 μmole amounts of conjugated glyoxal without a prior liberation process. Data for glyoxal content obtained by this procedure are discussed in relation to overoxidation.     

Electrophoretic and spectrophotometric determination of triiodides of sulfur-containing organic cations

Trimethylsulfonium triiodide (I) and p-xylylene-bis-(tetrahydrothiophenium) triiodide (II) were identified and determined by capillary electrophoresis with the resolution R _s = 4.86 using an unmodified quartz capillary. The procedure ensures the determination of sulfur-containing organic compounds in a concentration range of 1.0 × 10^?5–5.0 × 10^?4 M RSD ≤ 5%). The high stability of trimethylsulfonium triiodide and p-xylylene-bis-(tetrahydrothiophenium) triiodide in chloroform and acetonitrile solutions was found by spectrophotometry. A procedure was proposed for the spectrophotometric determination of compounds I and II as ion associates of sulfur-containing cations with a sulfophthalein dye, Bromocresol Purple (c _min (I) = 1.32 × 10^?5 M, c _min (II) = 7.1 × 10^?6 M, RSD = 5%), and by the characteristic absorption of the triiodide anion in acetonitrile (c _min (I) = 3.18 × 10^?6 M, c _min (II) = 2.76 × 10^?6 M, RSD <-3%).     

Sorption of a complex of europium (III) with acetylacetone on hydrophobized hexadecyl silica gel and hyper crosslinked polysterene

The sorption of a complex of europium (III) with acetylacetone on silica gel chemically modified with hexadecyl groups (SiO₂-C₁₆) and hyper crosslinked polystyrene (HLPS) was studied. Maximum extraction was observed at pH 5–7 when SiO₂-C₁₆ was used as the sorbent and at pH 4–7 in the case of crosslinked polystyrene. The partition coefficients for HLPS and silica gel were calculated as 7 × 10³ and 1 × 10² cm³/g, respectively. Quantitative extraction of the europium (III) complex was possible in dynamic conditions using a microcolumn (length, 10 mm; internal diameter, 3mm) packed with HLPS at pH 5 (10–50 mL sample volume). Desorption of europium using solutions of nitric acid at different concentrations was investigated. Quantitative desorption was achieved using 5 mL of 1 M HNO₃. A linear range of detection was observed at an amount of europium from 5 to 25 μg in a 10-mL sample (650 nm).     

Sensitive fluorescent probes for determination of hydrogen peroxide and glucose based on enzyme-immobilized magnetite/silica nanoparticles

Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme horseradish peroxidase (HRP) on Fe₃O₄/SiO₂ magnetic core–shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe₃O₄/SiO₂ nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able to activate hydrogen peroxide (H₂O₂), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm. Under optimized conditions, a linear calibration curve was obtained over the H₂O₂ concentrations ranging from 5.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 2.1 × 10⁻⁹ mol L⁻¹. By simultaneously using glucose oxidase and HRP-immobilized Fe₃O₄/SiO₂ nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity of the product responded well linearly to glucose concentration in the range from 5.0 × 10⁻⁸ to 5.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 1.8 × 10⁻⁸ mol L⁻¹. The proposed method was successfully applied for the determination of glucose in human serum sample.     

Extraction of PCDD/PCDF from soil with supercritical CO2: Optimization by a three-level factorial design approach

A highly sensitive and selective voltammetric procedure is described for the simultaneous determination of eleven elements (Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe) in water samples. Firstly, differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode (HMDE) is used for the direct simultaneous determination of Cd, Pb, Cu, Sb and Bi in 0.1 M HCl solution (pH = 1) containing 2 M NaCl. Then, differential pulse cathodic stripping voltammetry (DPCSV) is used for the determination of Se in the same solution. Zn is subsequently determined by DPASV after raising the pH of the same solution to pH 4. Next, the pH of the medium is raised to pH 8.5 by adding NH₃/NH₄Cl buffer solution for the determination of Mn by DPASV. Ni and Co are determined in the same solution by differential pulse adsorptive stripping voltammetry (DPAdSV) after adding DMG (1 × 10^–4 M). Finally, 1 × 10^–5 M 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is added to the solution for the determination of Fe by DPAdSV. The optimal conditions are described. Relative standard deviations and relative errors are calculated for the eleven elements at three different concentration levels. The lower detection limits for the investigated elements range from 1.11 × 10^–10 to 1.05 × 10^–9 M, depending on the element determined. The proposed analysis scheme was applied for the determination of these eleven elements in some ground water samples.     

Development of a stable biosensor based on a SiO2 nanosheet–Nafion–modified glassy carbon electrode for sensitive detection of pesticides

SiO₂ nanosheets (SNS) have been prepared by a chemical method using montmorillonite as raw material and were characterized by scanning electron microscopy and X-ray diffraction. SiO₂ nanosheet–Nafion nanocomposites with excellent conductivity, catalytic activity, and biocompatibility provided an extremely hydrophilic surface for biomolecule adhesion. Chitosan was used as a cross-linker to immobilize acetylcholinesterase (AChE), and Nafion was used as a protective membrane to efficiently improve the stability of the AChE biosensor. The AChE biosensor showed favorable affinity for acetylthiocholine chloride and catalyzed the hydrolysis of acetylthiocholine chloride with an apparent Michaelis–Menten constant of 134 μM to form thiocholine, which was then oxidized to produce a detectable and fast response. Based on the inhibition by pesticides of the enzymatic activity of AChE, detection of the amperometric response from thiocholine on the biosensor is a simple and effective way to biomonitor exposure to pesticides. Under optimum conditions, the biosensor detected methyl parathion, chlorpyrifos, and carbofuran at concentrations ranging from 1.0?×?10^?12 to 1?×?10^?10?M and from 1.0?×?10^?10 to 1?×?10^?8?M. The detection limits for methyl parathion, chlorpyrifos, and carbofuran were 5?×?10^?13?M. The biosensor developed exhibited good sensitivity, stability, reproducibility, and low cost, thus providing a new promising tool for analysis of enzyme inhibitors.

Electrochemical behaviors and determination of melamine in neutral and acid aqueous media

The electrochemical behaviors of melamine (MEL) were studied at paraffin-impregnated graphite electrode in PBS (pH 7.0) and 0.5 M H₂SO₄. Various methods including UV–vis thin-layer spectroelectrochemistry, infrared spectra (IR) and electrochemicatry have been performed to investigate the characteristics. In 0.1 M PBS (pH 7.0), MEL loses two electrons to form a dication, which couples head-to-head with a neutral molecule of MEL to form a dimer accompanying the production of azocompound, the dimer plays a role of a monomer in the following polymerization. In 0.5 M H₂SO₄, unstable MEL mostly hydrolyzes to form ammeline, ammelide, s-triazine-2,4,6-trion, and tricyanic acid, respectively; The hydrolysis could be accelerated by electrochemical method; Meanwhile, MEL associates tricyanic acid to give a plane molecule cake by hydrogen bonding. The spectra responses of MEL at 205 and 234 nm are linearly increasing in a same concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻⁵ M in 0.5 M H₂SO₄ (determination limit, 1 × 10⁻⁸ and 3 × 10⁻⁸ (3σ)). The proposed method was successfully applied to the determination of MEL in real sample.

     

Solid-phase luminescence determination of tetracycline in bottled water using chemically modified silica

Possibility of using chemically modified silica (CMS) with covalently immobilized sulfonic and ethylenediaminetriacetate (ED3A) groups for the adsorption preconcentration and extraction of tetracycline (TC) from aqueous solutions is studied. The conditions of complex formation by europium(III) ions on the surface of these adsorbents are optimized. The effect of citrate and Eu³⁺ ions on the luminescence intensity of the Eu–TC complex is shown. The luminescence properties of SiO₂ED3AEu and SiO₂SO₃HEu systems with tetracyclines are studied depending on the acidity of the medium, time of phase contact, the ratio of the volume of the solution to the weighed portion of the adsorbent, and concentrations of the adsorbed substances. It is found that tetracycline is quantitatively extracted by CMS as a complex with europium(III) ions in pH range 6.5–8.0; adsorption capacity to tetracycline in the Henry region is as high as 0.07–0.09 mmol/g and partition coefficients are 10³–10⁴ mL/g. A procedure is developed for the solid-phase luminescence determination of tetracycline using SiO₂SO₃HEu and SiO₂ED3AEu systems with limits of detection of 0.8 and 2.0 nM, respectively; linearity range is 1 × 10^–9–1 × 10^–5 M. The procedure is tested in the analysis of model mixtures and samples of bottled water.     

The Electropolymerization of 2,6‐Diaminopyridine and Its Application as Mercury Ion Selective Electrode

A composite graphite (CG) electrode modified with poly(2,6‐diaminopyridine) (PDAP) was used as solid state‐ion selective electrode for determination of mercury. The electrooxidation of monomer 2, 6 diaminopyridine (DAP) onto CG was accomplished from the 30 mM DAP in 5% H₂SO₄ and 0.5 M ZnSO₄. The electrode displayed Nernstian response with slope of 28.4±1 mV decade⁻¹ in concentration range of 1×10⁻⁶ to 1×10⁻¹ M and in solution of pH 3–5. The limit of detection for electrode was 3×10⁻⁸ M with response time of 25 s. The electrode was also suitable as an indicator electrode in the potentiometric titration of Hg²⁺ with iodide.     

Electrochemical determination of 5-hydroxytryptamine using mesoporous SiO<Subscript>2</Subscript> modified carbon paste electrode

A mesoporous SiO₂ was synthesized according to the published work, and then used to modify the carbon paste electrode (CPE). The electrochemical behaviors of 5-hydroxytryptamine (5-HT) at the bare CPE and the mesoporous SiO₂ modified CPE were compared. Owing to the huge surface area, unique mesopores and strong adsorptive ability, the oxidation signal of 5-HT at the mesoporous SiO₂ modified CPE greatly increased, compared with that at the bare CPE. This clearly suggests that the mesoporous SiO₂ modified electrode shows efficient and remarkable enhancement effect towards 5-HT. Based on this, a sensitive, rapid and convenient electrochemical method was developed for the determination of 5-HT after optimizing the experimental parameters such as supporting electrolyte, content of mesoporous SiO₂ as well as accumulation time. The linear range is from 2.0 × 10⁻⁷ to 1.5 × 10⁻⁵ mol/l, and the limit of detection is as low as 8.0 × 10⁻⁸ mol/l after 2-min accumulation. The relative standard deviation (RSD) for 10 mesoporous SiO₂ modified CPEs is evaluated to be 6.7%. Finally, this novel method was successfully used to determine 5-HT in human blood serums.     

Voltammetric determination of B<Subscript>1</Subscript> and B<Subscript>6</Subscript> vitamins using a pencil graphite electrode

Due to the importance of B₁ and B₆ vitamins for human health it is useful to develop new cheap and rapid methods for their determination. Voltammetric behavior of these vitamins on a pencil graphite electrode was investigated using cyclic voltammetry in different media. Direct quantitative determination of the two vitamins, one in the presence of the other, was done by differential pulse voltammetry. Vitamin B₁ was electroactive only in a NaOH solution generating two irreversible oxidation peaks; the first peak obtained at 250 mV is well-defined and was used in quantitative determinations. In case of vitamin B₆, a well-defined oxidation peak was observed in all investigated supporting electrolytes except for HCl. The linear concentration ranges were 10^?5–10^?3 M for vitamin B₁ in a NaOH solution and 5 × 10^?6–10^?3 M for vitamin B₆ in an acetate buffer solution. The obtained detection limits were 5.34 × 10^?6 M and 2.81 × 10^?6 M for vitamin B₁ and vitamin B₆, respectively. The developed method is simple and rapid and it was successfully applied in the determination of the two vitamins in pharmaceuticals.     

Nonenzymatic determination of glucose on electrodes prepared by directed electrochemical nanowire assembly (DENA)

The analytical characteristics of gold nanowires prepared by direct electrochemical synthesis were studied with the use of the amperometric determination of glucose as an example. The applicability of the gold nanowires to the determination of glucose in a neutral medium (a phosphate buffer solution with pH 7.2) over a concentration range from 1 × 10^–4 to 5 × 10^–3 M at a detection potential of +0.35 V was shown. It was found that the sensitivity of a nonenzymatic sensor for the determination of glucose on the gold nanowires was high: 3.7 × 10^–4 A M^–1 m^–2. The limit of detection was 3.3 × 10^–5 M.     

Differential kinetic thermal lens determination of aniline and 4-nitroaniline

Thermal lens spectrometry was used for the differential kinetic determination of aniline (over the concentration range of 8 × 10⁻⁴–3.2 × 10⁻³ M) and 4-nitroaniline (2 × 10⁻⁴–1.6 × 10⁻³ M) present in combination in a single sample based on the oxidation reaction with periodate ions in an acidic medium (this determination is not possible with the spectrophotometric monitoring of the rate of reaction). The thermal lens procedure (λ_e = 488.0 nm; 80 mW) was characterized by good performance characteristics in the determination of aniline (c _min = 3 × 10⁻⁴ M; c _d = 8 × 10⁻⁴ M) and 4-nitroaniline (c _min = 7 × 10⁻⁵ M; c _d = 2 × 10⁻⁴ M), simplicity, and rapidity.     

Praseodymium Doped Dysprosium Oxide-carbon Nanofibers Based Voltammetric Platform for the Simultaneous Determination of Sunset Yellow and Tartrazine

A platform based on praseodymium doped dysprosium oxide-carbon nanofibers modified electrode was constructed for the simultaneous determination of SY and TAR. SEM, EDX and XRD techniques were utilized for characterizing the proposed material. The voltammetric behaviour and properties of SY and TAR were gradually improved at materials in order from CNFs to Dy₂O₃−CNFs and Pr₆O₁₁@Dy₂O₃−CNFs. The working range was found to be 1.0×10⁻⁹–3.5×10⁻⁸ M and 1.5×10⁻⁹–4.0×10⁻⁸ M for SY and TAR, respectively. The value of LOD was 3.12×10⁻¹⁰ M and 5.35×10⁻¹⁰ M for SY and TAR, respectively. The platform (Pr₆O₁₁@Dy₂O₃−CNFs/GCE) was successfully applied to the electroanalysis of samples.     

Selected rotational level lifetimes and singlet-triplet coupling in the S1 state of glyoxal

The fluorescence collision-free lifetimes were measured for a few rotational levels of the O° S₁ state of glyoxal using a single-mode Ar⁺ laser. Decays are exponential over 5–6 lifetimes and variation of τ^1.k_o does not exceed 5%. The higher limit of singlet-triplet mixing coefficient β² ? 3 × 10^?2 is deduced from the lifetime measurements. The efficiency of collision induced intersystem crossing and its relation with <β² > value is discussed. ISC is absent in collision-free conditions for deuterated glyoxal as it is known to be for protonated glyoxal.