Parabens determination with a hybrid FIA/HPLC system with ultra-short monolithic column

The combination of an ultra-short C18 monolithic column (5 mm long) with a flow injection analysis (FIA) scheme results in a versatile and efficient system that has been used for the chromatographic determination of four preservatives — methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). The separation is carried out by using two carriers, A and B, consisting of a mixture of ACN: water in different proportions. The described procedure is able to separate the analytes in only 150 s. The applicable concentration range, detection limit and the relative standard deviation were the following: for MP from 1.6 × 10^-5 to 1.1 × 10^-3 M; 4.8 × 10^-4 M; 0.65%; for EP between 3.7 × 10^-5 and 2.0 × 10^-3 M; 1.2 × 10^-5 M; 1.2%; for PP between 3.9 × 10^-5 and 2.0 × 10^-3 M; 1.2 × 10^-5 M; 1.2%; and for BT between 6.0 × 10^-5 and 2.0 × 10^-3 M; 1.8 × 10^-5 M; 1.8%. The method was applied and validated satisfactorily for the determination of these parabens in commercial cosmetics samples, comparing the results with those obtained by HPLC reference method.     

Electrocatalytic determination of hydroquinone with Mn+ modified gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer electrodes

Application of immobilized metal cations on the topside of gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer (Au-5A2MBI-Mⁿ⁺ SAM, Mⁿ⁺:Cu²⁺ or Ag⁺) for electrocatalytic determination of hydroquinone (H₂Q) is described by voltammetric method. Several parameters were investigated to evaluate the performance of the sensors. Calibration curves for H₂Q concentrations were linear from 1.0 × 10^-5 to 4.0 × 10^-4 M (r = 0.998) for Au-5A2MBI, from 1.0 × 10^-5 to 6.0 × 10^-4 M (r = 0.998) for Au-5A2MBI-Cu²⁺, and from 2.0 × 10^-6 to 2.0 × 10^-5 M (r = 0.996) and 1.0 × 10^-4 to 1.0 × 10^-3 M (r = 0.991) for Au-5A2MBI-Ag⁺ SAM modified electrode. The respective detection limits were found as 6.5 × 10^-6, 4.6 × 10^-6 and 1.8 × 10^-7 M. Both Cu²⁺ and Ag⁺ ions were found to have a good electrocatalytic effect on the oxidation of H₂Q; however, Ag⁺ was a more effective catalyst and showed better sensitivity and lower detection limit than all other tested electrodes. Au-5A2MBI-Ag⁺ SAM electrode was used as a suitable sensor for determination of H₂Q in a radiolysis developing agent as real sample. The results obtained by using proposed sensor and that obtained by an ASTM reference method were in good agreement at the 95% confidence level.     

Voltammetric behavior of neptunium(vi) in glutamic acid media at the rotating glassy carbon electrode

The voltammetry of neptunium(VI) glutamate was investigated over the pH range 3.8–10.0. A reversible, one-electron wave was obtained for glutamate concentrations above 0.1 M in the pH range 3.8–6.1, or above 0.3 M in the pH range 6.1–10.0. At pH 3.8–6.1, the half-wave potential was independent of pH, but at pH 6.1–10.0, it was a function of pH. The metal-ligand ratio was found to be 1:2 by conductometric titration. The limiting current was proportional to the concentration of the neptunium(VI) from 7.83·10^-5 to 1.96·10^-3M. The diffusion coefficient was 0.35·10^-5 cm² sec^-1 at pH 4.5 and 0.30·10^-5 cm² sec^-1 at pH 9.4.     

Amperometric Biosensor for the Determination of Phenols Using a Crude Extract of Sweet Potato (Ipomoea Batatas (L.) Lam.)

Abstract

An amperometric biosensor for the determination of phenols is proposed using a crude extract of sweet potato (Ipomoea batatas (L.) Lam.) as an enzymatic source of polyphenol oxidase (PPO; tyrosinase; catechol oxidase; EC 1.14.18.1). The biosensor is constructed by the immobilization of sweet potato crude extract with glutaraldehyde and bovine serum albumin onto an oxygen membrane. This biosensor provides a linear response for catechol, pyrogallol, phenol and p-cresol in the concentration ranges of 2.0×10^?5-4.3×10^?4mol L^?1, 2.0×10^?5-4.3×10^?4 mol L^?1, 2.0×10^?5-4.5×10^?4 mol L^?1 and 2.0×10^?5-4.5×10^?4mol L^?1, respectively. The response time was about 3–5 min for the useful response range, and the lifetime of this electrode was excellent for fifteen days (over 220 determinations for each enzymatic membrane). Application of this biosensor for the determination of phenols in industrial wastewaters is presented.     

Extraction—spectrophotometric determination of palladium(ii) with 2-nitroso-5-diethylaminophenol

An extraction—spectrophotometric determination of palladium(II) with 2-nitroso-5-diethylaminophenol is described. Complex formation and extraction of the complex with chloroform are possible with aqueous phases of about 2.5 M sulfuric acid. The molar absorptivity of the complex is 4.38 X 10⁴ l mol^-1 cm^-1 at 486 nm. Few of the common ions interfere at concentrations of 10^-4–10^-3 M; more than 10^-5 M Ir(IV), 10^-5 M W(VI), 5 × 10^-6 M Au(III) and 10^-6 M iodide cause negative errors. The method can be applied to the determination of palladium in catalysts for automobile exhaust purifiers.     

Determination of Psoralen and Isopsoralen in Traditional Chinese Medicines by Capillary Zone Electrophoresis with Amperometric Detection

A simple, reliable and reproducible method was developed for determination of psoralen and isopsoralen in several traditional Chinese medicines, such as Shouwu Pian, Gubenkechuan Pian, was described in this paper. It was based on capillary zone electrophoresis with amperometric detection (CZE-AD). A carbon-disc electrode was used as working electrode. The optimal conditions of separation and detection were pH7.6 phosphate buffer (20 mM), 20 kV for the separation voltage and 1.00V (vs. Ag/AgCl) for the detection potential. The linear ranges were 6.90 × 10^-5~1.30 × 10^-7 mol L^-1for psoralen and 5.0 × 10^-5~1.80 × 10^-7 mol·L^-1 for isopsoralen with the correlation coefficient of 0.9984 and 0.9994, respectively. The detection limits for psoralen and isopsoralen were 4.2 × 10^-8 mol·L^-1 and 6.0 × 10^-8 mol·L^-1 based on the signal to noise ratio of 3. The method built in this paper was directly applied to the determination of several traditional Chinese medicines with some simple pretreatment. The assay result was satisfactory.     

Electrophoretic and gas-chromatographic analysis of an Afobazol pharmaceutical preparation

Procedures for determining 5-ethoxy-2-[2-(morpholino)ethylthio]benzimidazole dihydrochloride, an active component of the Afobazol medicinal preparation, and its potential impurities, 5-ethoxybenzimidazol-2-thione and N-(2-chloroethyl)morpholine hydrochloride by capillary zone electrophoresis in the range 2.0 × 10^?5 to 2.0 × 10^?3 M and ligand-exchange capillary electrophoresis in the range 1.0 × 10^?5 to 5.0 × 10^?3 M are developed. The optimum conditions for the separation and determination of these analytes using a quartz capillary tube are found. The reliability of the results obtained by capillary electrophoresis was confirmed by gas chromatography with a mass-selective detector.     

Die bestimmung von alizarin s nach der anreicherung am stationären quecksilbertropfen und ihre anwendung zur fluoridanalyse

Traces of alizarin S can be concentrated on the stationary mercury electrode. The lower limit for the production of d.c. voltammograms is 5·10^-9M. The voltammetric spectrum of the dyestuff was examined by means of d.c. and a.c. polarographic techniques. An indirect voltammetric method for the determination of fluoride in the range 5·10^-7–5·10^-6M is suggested.     

Sunscreen Protection Against Ultraviolet Radiation-induced Pyrimidine Dimers in Mouse Epidermal DNA

Pyrimidine dimers were measured in epidermal DNA of SKH:HRI mice following exposure to solar-simulated UV radiation (SSUV, 290–400 nm) or to UVA (320–400 nm). Mice were exposed to SSUV or UVA after topical application (2 mg/cm²) of vehicle, a UVB absorber (5% 2-ethylhexyl p-methoxycinnamate [2-EHMC]), or a broad-spectrum UVA absorber (5% Mexoryl®SX). The rates of induction of pyrimidine dimers in untreated animals were 5.4 ± 0.57 times 10^-4 (mean ± SEM) and 7.6 ± 0.95 times 10^-6 dimers per 10⁸ Da of epidermal DNA per J/m² of SSUV and UVA, respectively. Topical application of Mexoryl®SX reduced the rate of induction of pyrimidine dimers in SSUV-exposed animals to 4.7 ± 0.44 times 10^-5 dimers per 10⁸ Da per J/m² for a dimer induction protection factor (PF) of 11.5 (5.4 times 10 ⁴/4.7 times 10^-5). The rate of dimer induction in Mexoryl®SX-treated, UVA-ex-posed mice was 0.95 ± 0.2 times 10^-6 dimers per 10⁸ Da per J/m² (PF = 8.0). The 2-EHMC at a concentration of 5% (wt/wt) was significantly less effective than Mexoryl®SX in preventing the induction of pyrimidine dimers in animals exposed to either SSUV or UVA. The rates of dimer induction in 2-EHMC-treated mice were 8.2 ± 1.1 times 10^-5 and 3.8 ± 0.33 times 10^-6 dimers per Da per J/m² of SSUV (PF = 6.6) and UVA (PF = 2.0), respectively. Upon normalizing to the efficacy for edema induction, UVA induced approximately one-fourth the number of pyrimidine dimers per equivalent edematous response when compared to SSUV.     

The Characteristics of Green Calcium Oxide Derived from Aquatic Materials

Thermogravimetric Analysis of three aquatic materials, i.e. cuttlebone, mussel shell and oyster shell, and other physicochemical characteristics were investigated. The highest decomposition rates of aquatic materials under two surrounding gases, i.e. oxygen and nitrogen, exhibited no significant difference for cuttlebone (3.6×10^-5-4.8×10^-5 mg s^-1 mg_initial^-1 at heating rate 5 °C/min and 11.8 ×10^-5 -12.5×10^-5 mg s^-1 mg_initial^-1 at heating rate 15 °C/min) and mussel shell (3.4×10^-5- 5.2×10^-5 mg s^-1 mg_initial^-1 at heating rate 5 °C/min and 11.9×10^-5 – 12.4×10^-5 mg s^-1 mg_initial^-1 at heating rate 15 °C/min), while oyster shell provided the higher decomposition rate under nitrogen surrounding gas (7.6×10^-4 mg s^-1 mg_initial^-1 at heat rate 5 °C/min and 21.53×10^-4 mg s^-1 mg_initial^-1 at heating rate 15 °C/min). This is probably because of the difference in their starting crystalline structures, i.e. aragonite (cuttlebone and mussel shell) and calcite (oyster shell). The cubic calcium oxides were prepared by calcination of three aquatic materials under oxygen and nitrogen surrounding gases at 5 °C/min ramping to 850 °C for 2 hours. All resulting calcium oxides obtained from oxygen atmosphere provided only cubic crystalline phases and the adsorption-desorption isotherms (IUPAC Type III), whereas the calcinations under nitrogen surrounding gas gave a presence of calcium hydroxide crystalline or hydroxyl- contaminate existing with cubic calcium oxide that influences on the strength and the number of carbon dioxide adsorption sites. The specific surface area of all resulting calcium oxides ranged from 0.1 – 1.5 m²/g and the average pore diameter was found in the range of 40-60 nm. The the number of basic sites belonging to CaO derived from Oyster shell or Cuttlebone were improved while firing under oxygen atmosphere. The suitable firing condition is at the low heating rate to develop porous materials.     

Fluoride in sea water: intercalibration study based on electrometric and spectrophotometric methods

Fluoride was shown to be a conservative constituent of sea water. Samples from the eastern tropical North Pacific, the Caribbean, the Labrador Basin, and the Reykjanes Ridge region indicated that the most probable $\text{F}\text{Cl}$ ratio in sea water is 6.71·10^-5 with an overall uncertainty of ±0.07·10^-5 based on 99% confidence limits of ±0.02·10^-5 and an allowance of ±0.05· 10^-5 for systematic error. Double-blind measurements from laboratories using electrometric and spectrophotometric methods agreed closely. Mean $\text{F}\text{Cl}$ ratios found were all within 0.7% of the most probable value.     

Study on the Fluorescence System of Tb-ATP-Phen for the Determination of ATP

Abstract

It was found that ATP could form a ternary complex with Tb³⁺ and Phen, which can emit the characteristic fluorescence of Tb³⁺. The experiment showed that the fluorescence intensity of the system was maxmium in the following conditions: pH of the solution is 7.2, the concentrations of Tb³⁺ and phenanthroline (Phen) are 2.0×10^-5mol.L^-1 and 2.0 × 10^-4mol.L^-1, respectively. At the optimum conditions, a linear relationship is obtained between the fluorescence intensity and ATP concentration in the range of 1.0×10^-6—1.0×10^-5mol.L^-1.

Traces of ATP in drugs (ATP disodium salt tablets) can be determined using the standard addition method. The luminescence mechanism of the system was discussed.     

Determination of 99Tc in environmental samples by anion exchange and liquid-liquid extraction at controlled valency

A method for collecting ⁹⁹Tc from 200-2-400 1 of sea water by anion exchange has been developed. Further decontamination of ^103.106Ru was achieved by repeated evaporation of RuO₄ from 0.05 M sulphuric acid at 100° C, followed by extraction of TcO^-₄ into 5% triisooctylamine-xylene at controlled valency. ^110mAg was precipitated as AgCl. An average overall radiochemical yield of 70% was found for Tc. Decontamination factors were between 3 10⁵ and 2 10⁷ for Ru and 2 10⁵ for Ag. A method for determining ⁹⁹Tc in seaweed by wet ashing and simple extraction into 5% triisooctylamine-xylene is also presented.     

A highly efficient radical clock as a probe of the mechanism of sulfone halogenation by perhaloalkanes

Halogenation of (endo)-5-(2-i-propylsulfonyl)-2-norbornene 5, a new highly efficient radical probe, shows that if an SET mechanism was occurring in the -α-halogenation of sulfones by perhaloalkanes, it would have to involve a reaction step in which a C-centered radical reacts with CX₄^$\text{.}$ at a rate greater than 10¹⁰ s^?1.     

Enzymatic inhibition enthalpimetry: The analytical potential of the inhibitory action of a series of physiologically active alkaloids on the activity of serum cholinesterase

A kinetic method is described for the enthalpimetric determination of a series of physiologically active alkaloids based on their inhibitory effect on the cholinesterase-catalysed hydrolysis of butyrylcholine iodide. All analyses are done at pH 8.0 and at 25.0°C (short term stability ± 0.002°C). Precision (< 3.0%) data are reported for the determination of physostigmine sulphate (1.0–4.0 × 10^-8), quinine sulphate (1.0 × 10^-6–4.0 × 10^-5), procaine hydrochloride (1.0 × 10^-5–× 2.5 × 10^-4), atropine sulphate (5.0 × 10^-5–3.0 × 10^-4), morphine sulphate (1.0–8.0 × 10^-4), codeine phosphate (3.0 × 10^-4–2.4 × 10^-3), pilocarpine nitrate (5.0 × 10^-4––6.0 × 10^-3) and thiamine hydrochloride (1.0–5.0 × 10^-3); the linear response ranges in mol dm^-3 are given in parentheses. Complete inhibition curves are presented and relative “potency” is inferred. The effects of several interfering inhibitors are discussed.     

Contamination of water and organic solvents stored in plastic bottles with phthalate ester plasticizers

Migration of phthalic acid esters into water, n-hexane, and methanol kept in polyethy-lene bottles or PVC tubes was investigated by high-performance liquid chromatography with a variable wavelength u.v. detector. The content of esters in water kept in contact with PVC for one day was 0.44 ppm and the migration rate of dibutyl phthalate was 4.8 × 10^-5 mg h^-1 cm^-2 of PVC tube. n-Hexane stored in a polyethylene bottle for 7 days contained 6 ppm esters; the migration rate of dibutyl phthalate was 6.4 × 10^-5 mg h^-1 cm^-2 of polyethylene. PVC tubing connected to ion-exchange resin columns contaminates deionized water with the esters.     

Potential cerebral perfusion agents. Synthesis and evaluation of a 1,4-disubstituted dihydropyridine analogue

The synthesis of a 1,4-disubstituted dihydropyridine, 1-(E-1[¹²⁵I]iodo-1-penten-5-yl)-4-(β-N-acetylaminoethyl)-1,4-dihydropyridine ([¹²⁵I] 10 ), is described. Acetylation of 4-(β-aminoethylpyridine) with acetic anhydride followed by condensation with E-1-borono-5-iodo-1-pentene ( 7 ) gave 1-(E-1-borono-1-penten-5-yl)-4-(β-N-acetylaminoethyl)pyridinium iodide ( 8 ). Chloramine-T and sodium iodide iodination of 8 gave the corresponding E-1-iodo compound 9 which was reduced with sodium borohydride to furnish 1-(E-1-iodo-1-penten-5-yl)-4-(β-N-acetylaminoethyl)-1,4-dihydropyridine ( 10 ). The corresponding radioiodinated compound was prepared similarly using Na[¹²⁵I]. The tissue distribution studies in rats indicate that [¹²⁵I] 10 crosses the blood brain barrier (0.49% dose/g in the brain) but gradually washes out from the brain.     

Potassium ion-selective membrane electrodes based on naphtho-15-crown-5

The potassium-selective PVC membrane electrodes based on naphtho-15-crown-5 have rapid, stable and Nernstian response in the range 10^-1–10^-5 M. The selectivity coefficient for potassium over sodium is 4 × 10^-4.     

Determination of iron(II) and iron(III) by flow injection and amperometric detection with a glassy carbon electrode

Flow injection analysis can be used for the determination of both iron(II) and iron(III) with an amperometric detector. The flow-through cell contains a glassy carbon electrode. Selection of the appropriate voltammetric technique, choice of the indication potentials, sample size, composition of the carrier stream, etc., are discussed. The limit of determination is about 10^-6 M; the calibration curves are linear in the concentration ranges 10^-3–10^-5 M for iron(III) and 5 × 10^-4–10^-5 M for iron(II). To illustrate the potentialities of the proposed method, standard rocks have been analysed.     

Differential pulse anodic stripping voltammetry of copper(II) at the glassy carbon electrode

Optimum conditions for the use of the bare glassy carbon electrode (GCE) are reported. Linear calibration graphs are obtained in the range 5 × 10^-7–3.5 × 10^-5 M copper(II). The detection limit for copper(II) is 5.9 × 10^-9 M at pH 4.5 and 3.3 × 10^-8 M at pH 6.5.