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.     

Study of Fluorescence System of Gmanylic Acid-Tb3+ and the Determination of Gmanylic Acid

Abstract

It was found that gmanylic acid (GMP) can be selectively completed with Tb³⁺ at pH 6.0-6.6, which then emits strong fluorescence characteristic of Tb³⁺. This reaction can be used for the determination of GMP in presence of adenylic acid (AMP), uridylic acid (UMP) and cylidylic acid (CMP). A linear relationship is obtained between the fluorescence intensity and GMP concentration in the range of 2.0×10^?7 - 1.0×10^?4M. The detection limit is 2.0×10^?8 M. The results showed that the composition ratio and apparent stability constant of GMP-Tb complex were 1:1 for GMP Tb³⁺- and 2.3×10^?5, respectively.     

Indirect Differential Pulse Voltammetric Determination of Aluminum Biological Samples in the Presence of 3, 4-Dihydroxyphenylalanine

ABSTRACT

Indirect differential pulse voltammetric (DPV) determination of aluminum in the presence of 3, 4-dihydroxyphenylalanine (L-dopa) with glass carbon electrode as working electrode has been described. The method relies on the decrease of DPV anodic peak current of L-dopa with the addition of Al^III The decreasing value of the peak current is linear with the increase of Al^III concentration. Under the optimum experimental conditions (pH 4.8, 6×10^?4 M L-dopa, 0.06M NaAc - HAc ¹buffer solution), the linear ranges are 4.0×10^?7 - 5.2×10^?6 M and 7.2×10^?6 - 4.5×10^?5 M. The relative standard deviation for 8×10^?6 M aluminum is 1.0% (n = 8) and the detection limit is 3.5×10^?7 M. A number of foreign species for interference have been studied. The method has been applied to determine aluminum in drinking water, synthetic renal dialysate and urine samples.     

Cyclodextrin induced room temperature phosphorescence of some polyaromatic hydrocarbons and nitrogen heterocycles in the presence of cyclohexane

Room temperature phosphorescence (RTP) of some polyaromatic hydrocarbons (PAHs) and nitrogen heterocycles (NHC) can be induced in the β-cyclodextrin cyclohexane (CD/CH) system. RTP spectra characteristics of these compounds in the system are investigated. Different actions for cyclohexane and bromoalkane in β-cyclodextrin induced RTP are suggested. In the CD/CH system the limits of phenanthrene and 7,8-benzoquinoline may reach 2.3 × 10⁻⁷ M and 4.5 × 10⁻⁷ M, respectively. The relative standard deviation (RSD) is less than 7.6%.     

Simultaneous Determination of Platinum and Palladium by Second Derivative Spectrophotometry Using 3-(2'-Thiazolylazo)-2, 6-Diaminopyridine as Chromophore Ligand

ABSTRACT

A second derivative spectrophotometric method has been developed for the determination of palladium and platinum in mixtures. The method is based on the formation of the platinum and palladium complexes with 3-(2-thiazolylazo)-2, 6-diaminopyridine, (2, 6-TADAP), in the presence of 1.7 M perchloric acid solution, upon heating at 90° C for 30 min and on the subsequent direct derivative spectrophotometric measurement. The zero-crossing approach and the graphic method were used for determination of platinum and palladium, respectively. Each analyte was determinated in the presence of one another in the ranges 8.9×10^-7 -3.1×10^-5 M for platinum and 4.6×10^-7 - 6.8×10^-5 M, for palladium. The detection limits achieved (3a) were found to be 2.7×10^-7 M of platinum and 1.4×10^-7 M of palladium. The relative standard deviations were in all instances less than 1.0%. In this work is included a study of effect of interferents and the application of the proposed method in synthetic mixtures.     

Flow-Injection Spectrophotometric Determination of Oxalate,Citrate and Tartrate Based on Photochemical Reactions

Abstract

A flow-injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochemical decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochemical reactions was detected by measuring the absorbance after complexation with ferrozine (λ_max=562 nm). Linear calibration graphs were obtained over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?4 M, 8 × 10^?6 - 1.8 × 10^?4 M and 1.0 × 10^?6 - 2 × 10^?5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1x10^?5 M concentration level were within the range 1.29 - 1.47 %. The sampling frequency was about 40 samples h^?1. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.     

Spectrofluorimetric Flow Injection Determination of Glycerol & Ethylene Glycol with Alizarin Navy Blue

ABSTRACT

A simple and accurate procedure for indirect spectrofluorimetric determination of glycerol and ethylene glycol in aqueous media was developed. Alizarin Navy Blue can be oxidized by potassium periodate to produce a fluorescent compound, that can be detected fluorimetrically (λ_ex = 370 nm, λ_em = 516 nm) by a flow through method. Glycerol and ethylene glycol react with periodate decreasing its concentration and thus the forming the basis for an indirect determination of these compounds. The influence of acid concentration, reagent concentration and manifold variables were studied. For glycerol and ethylene glycol linear calibration curves were obtained in the ranges of 4.8 × 10^-7 – 8.7 × 10^-5 M and 6.4 × 10^-7 – 8.7 × 10^-5 M, respectively. The limit of detection (defined as the concentration that gives a signal three times the standard deviation of the background signal) for glycerol and ethylene glycol was 3.2 × 10^-7 M and 4.3 × 10^-7 M, respectively. The proposed method was applied for determination of glycerol and ethylene glycol in synthetic and real samples. The results obtained were satisfactory.     

Sequential extraction partitioning of metals,sulfur, and phosphorus in bottom ash from a coal-fired power plant

Abstract

The herbicide trifluralin was analysed by adsorptive stripping voltammetry on a glassy carbon electrode. The linear concentration range was 2.5 × 10^?7 M – 1.25 × 10^?6M when using 5-min preconcentration at open circuit conditions in Britton-Robinson buffer of pH 7.0. The detection limit of trifluralin was 2.5 × 10^?8M. The relative standard deviation was 3.3% at a concentration of 1.0 × 10^?6M (n=5). The method was applied to the determination of trifluralin in soil with good recovery.     

Rapid Method for the Micro-Determination of Hydrazine by Amperometric Titration With Potassium Iodate

Abstract

An amperometric method, with potassium iodate as the titrant, for the rapid and precise determination of micro amounts of hydrazine salts is described. Hydrazine dihydrochloride, hydrazine sulfate and hydrazine hydrate could be quantitatively analyzed at the concentration range of 4 × 10^?7 -4×10^?3 M in the presence of 5 M hydrochloric acid. Hydrazine salts, 2×10^?4 -4×10^?3 M, were titrated in 5 minutes with a relative error and a relative standard deviation of 0.1%. It was also found that hydrazine dihydrochloride can be precisely determined, without any interference, even in the presence of hydroxylamine which is ten times as much as the former.

The suitable applied potential between the rotating platinum indicator microelectrode and the silver plate-silver chloride reference electrode was + 0.7V.     

Cathodic and Adsorptive Stripping Votammetry of Naftazone

Abstract

Naftazone (1,2-naphthoquinone-2-semicarbazone) undergoes a reversible two-electron transfer in both acidic and alkaline solutions and also gives rise at pH > 7 to an anodic wave attributed to the formation of a mercury derivative. Cathodic stripping voltammetry is proposed to determine the compound down to 5 × 10^?9 M after accumulation of its mercury salt formed at -0.05V in a 0.05M sodium hydroxide solution. These results have been compared with those obtained by performing an adsorptive collection of the drug in a pH 3 sodium perchlorate solution. Concentrations ranging from 1 × 10^?7 to 2 × 10^?7M can be easily investigated, the detection limit being 7 × 10^?11M. The influence of several operational parameters has also been considered.     

Electrocatalytic determination of dopamine in pharmaceutical and human serum samples by using [N,N′-bis(2-pyridine carboxamido)-1,2-benzene] nickel(II) modified carbon paste electrode

The main purpose of this study is to develop an inexpensive, simple, selective and especially sensitive modified carbon paste electrode (MCPE) for the determination of dopamine (DA) in pharmaceutical and human serum samples. The carbon paste electrode (CPE) has been modified by using [N,N′-bis(2-pyridine carboxamido)-1,2-benzene] nickel(II) complex (Ni(II)bpb) and the electrochemical behavior of the modified electrode has been studied by cyclic voltammetry. The modified electrode shows an excellent electrocatalytic effect on the oxidation of DA. Under optimum conditions, calibration plots are found to be linear in the range of 7.0 × 10⁻⁷−1.0 × 10⁻⁵ M (r ₂ = 0.9940) and 1.0 × 10⁻⁵−1.0 × 10⁻⁴ M (r₂ = 0.9945); the detection limit is 6.2 × 10⁻⁸ M. The preparation of MCPE is very easy. The electrode can be renewed by simple polishing. The proposed method shows good sensitivity, reproducibility (RSD ∼ 2.9%), high stability (more than two month) without any considerable change in response and recovery for the determination of DA. The prepared electrode has been successfully applied to the voltammetric determination of DA in pharmaceutical and biological samples. The article is published in the original.     

Electrochemical determination of prolintane in pharmaceutical formulations and in human urine

The oxidative behavior of 1-[1-(phenylmethyl)butyl]pyrrolidine, prolintane, was studied at a glassy carbon electrode using linear-sweep and differential-pulse voltammetry. The oxidation process was shown to be irreversible using 0.04 M Britton–Robinson buffer and was diffusion-adsorption controlled. Two voltammetric methods were developed for the determination of prolintane using different techniques: linear-sweep and differential-pulse voltammetry. The peak current varied linearly with prolintane concentrations in the range of 1.0 × 10⁻⁵ −2.5 × 10⁻⁴ M, with a detection limit of 8.5 × 10⁻⁶ and 4.0 × 10⁻⁶ M, and with relative standard deviations of 2.1 % and 3.1 %, respectively. The methods were applied to commercial preparations, giving relative errors less than 3.1 % and relative standard deviations lower than 4.8 % (n = 10). Determination of prolintane (down to the 8.5 × 10⁻⁸ M level) can be performed by using a preconcentration step prior to the determination by differential-pulse voltammetry in 0.04 M Britton–Robinson buffer (pH 8.0) with preconcentration potential of 0.0 V. The detection limit was found to be 6.2 × 10⁻⁸ M (4 min preconcentration) and the relative standard deviation for 2.5 × 10⁻⁷ M prolintane (n = 5) was 4.6 %. Applicability to human urine analysis is illustrated (recovery 98 ± 2 %). Standard additions method can be used to determine prolintane in real samples of urine.     

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.     

A Prospect for the Analysis of Species Acting as Enzyme Inhibitors as Illustrated by Heavy Metal Inhibition

Abstract

A flow system incorporating an amperometric glucose oxidase enzyme electrode has been used to study the inhibitory effects of 16 metal cations on glucose oxidase. Only copper(II), mercury(II) and silver(I) caused any significant inhibition. the enzyme electrode could be reactivated by EDTA, the reactivation being most effective for copper(II) and least so for silver(I). Other complexing agents were tried for reactivation but proved to be unsatisfactory.

The ability to reactivate the enzyme on the electrode following copper(II) inhibition, and the linear response of the system to the level of this inhibitor according to I/A = -9.49 × 10^?7 log([Cu]/M) + 4.84 × 10^?8; r = 0.994 between 2.5 × 10^?4M and 5 × 10^?3M [Cu]²⁺ indicates a prospect for the use of a flow system for determining enzyme inhibitors in samples.     

Zinc-Selective Membrane Electrode Based On 5, 6, 14, 15-Dibenzo-l, 4-Dioxa-8, 12-Diazacyclopentadecane-5, 14-Diene

ABSTRACT

A new PVC membrane for zinc ions based on DBDA15C4 as membrane carrier was prepared. The electrode shows a linear stable response over a wide concentration range (5.0 × 10^?5-1.0 × 10^?1 M) with a slope of 22 mV/decade and a limit of detection of 3.0 × 10^?5 M (2.0 μg/ml). It has a very short response time of less than 5 s and can be use for at least 11 months without any divergence in potential. The zinc ion-selective electrode exhibited very good selectivities with respect to alkali, alkaline earth and some transition and heavy metal ions and could be used in a pH range 1.5-7.0. It was successfully applied for the direct determination of zinc in a pharmaceutical sample and, as an indicator electrode, in potentiometric titration of Zn²⁺ ions.     

The Use of the CS2N− 3/HSO− 3/O2 Reaction for the Analytical Determination of Dissolved Oxygen

Abstract

A new analytical Spectrophotometric method has been developed for the determination of dissolved O₂ in the range 4.6 × 10^?6?4.1 × 10^?5M, based on the CS₂N^? ₃/HSO^? ₃/O₂ reaction. In one single experiment 2.3 × 10^?5 M of oxygen can be determined with an uncertainty of ± 7 × 10^?7M for a confidence level of 95%.     

Determination of lead by adsorption of the extracted 8-quinolinolate on the electrodes of a piezoelectric quartz crystal

Lead 8-quinolinolate extracted into chloroform is adsorbed on the electrodes of a piezoelectric quartz crystal. The change in frequency of the crystal is used to measure the lead concentration over the range 3 × 10^-6–5 × 10^-5 M in aqueous solution. The interferences of Fe(III), Ni, Co(II), Zn, Cd and Ag(I) can be masked byl-ascorbic acid and cyanide.     

Fluorescent microscopic determination of gatifloxacin in milk,injection, human urine,and rabbit serum samples by self-ordered ring technique on glass slides support

A simple and sensitive self-ordered ring (SOR) technique, which was based on the capillary effect of solvent on a hydrophobic glass slide, was successfully applied to the determination of gatifloxacin in milk, injection, human urine and rabbit serum samples. In a medium of pH 3.20 (HAc-NaAc) with the aid of poly(vinyl alcohol)-124 (PVA-124), when 0.50 μL aluminum-sensitized gatifloxacin was dropped on glass slide with dimethyl dichlorosilane (DMCS) pretreated, a typical fluorescent SOR with diameter (2R) of the ring less than ca. 1.77 mm and the belt width (2δ) less than 29.3 μm can be obtained. The solute on the ring belt had strong fluorescence. Data of the imaged SOR showed that the gatifloxacin molecule across the SOR belt section follows a Gaussian distribution. The assay showed that when the droplet volume is 0.1 μL, the SOR method could be used to determine gatifloxacin in the range of 5.61 × 10⁻¹⁴ ∼ 1.50 × 10⁻¹² mol/ring (5.61 × 10⁻⁸∼1.50 × 10⁻⁵ M) and the limit of determination (LOD) reached 5.61 × 10⁻¹⁵ mol/ring (5.61 × 10⁻⁸ M) with three-fold signal-to-noise ratio (S/N = 3).     

Disopyramide-Selective Membrane Electrode∗

Abstract

A liquid membrane electrode based on disopyramide - dipicrylamine ion - pair complex, dissolved in nitrobenzene as solvent was proposed for the determination of disopyramide - an antiarrhythmic drug. The linear response covers the range from 10^?2 - 5 × 10^?6 M disopyramide solution, with a slope of 51.0 mV/decade (pH range 3.0 to 7.0). The detection limit is 4.7 × 10^?8 M. The electrode shows a good stability, reproducibility and fast response. The selectivity of the electrode is good. The strong interfering ion is thiamine (Vitamin B₁). These characteristics of the electrode made it to be used for the determination of disopyramide through direct and indirect potentiometric methods. Through indirect potentiometric method, disopyramide - as active substance can be determined with an average recovery of 99.98% and a relative standard deviation of 0.24%, and also this method can be used for its determination in pharmaceutical formulations such as capsules and ampoules with a relative standard deviation less than 1%. The electrode can be used at the dissolution tests of disopyramide capsules. The physical processes are numerically simulated by typical equations. The apparent first - order rate constants for disintegration and dissolution processes were calculated.

     

Separation of hafnium from tungsten by extraction chromatography with TOA in HCl–H<Subscript>2</Subscript>O<Subscript>2</Subscript> mixture

In order to measure ¹⁸²Hf by accelerator mass spectrometry (AMS), a chemical procedure for separation of hafnium from tungsten has been developed by extraction chromatography. The extraction chromatographic behavior of hafnium and tungsten has been studied using tri-n-octylamine (TOA) as the stationary phase, HCl–H₂O₂ mixture and NH₃·H₂O as the mobile phase. The effects of H₂O₂ concentration, column loading and column dimensions are investigated. Hf and W with microgram amounts are successfully separated on a chromatographic column (Ø5 × 196 mm), on which Hf is hardly retained after completely eluted with 6 M HCl–1% H₂O₂ and W strongly adsorbed is then eluted with 3 M NH₃·H₂O. The decontamination factor for tungsten is 3.0 × 10⁵ and the recovery of hafnium is better than 99% using a single column separation.