Trace analysis of aluminum in natural waters with rubeanic acid by adsorption chronopotentiometry

The determination of trace levels of aluminum in natural waters with rubeanic acid (RA) by adsorption chronopotentiometry is developed in this paper. Optimum experimental conditions include an accumulation potential of -0.40 V, accumulation time of 60 s, and a RA concentration of 6x10(-6) M in 0.2 M NaAc-HAc buffer solution (pH 4.6). The response is linear over the 1x10(-8) approximately 4x10(-7) M concentration range. The detection limit is 5.6x10(-9) M and the relative S.D. (at the 3x10(-7) M level) is 2.6%. Possible interferences are evaluated. The method has been applied to the determination of trace levels of Al in various real samples. Direct determination of toxic forms of Al in surface waters by this technique is also explored.     

Hydroxy-thioxanthones as suitable neutral ionophores for the preparation of PVC-membrane potentiometric sensors for Al(III) ion.

The complexation of five recently synthesized hydroxy-thioxanthone derivatives with Al3+ ion was studied in a methanol solution spectrophotometrically, and the stepwise formation constants of the resulting 1:1 and 2:1 (ligand-to-metal) complexes were evaluated. The suitability of the thioxanthone derivatives as neutral ionophores for the preparation of a new Al3+ ion-selective PVC-membrane electrode was investigated, and 1-hydroxy-3-methyl-thiocanthone was selected as the best compound for this purpose. The prepared electrode exhibits a Nernstian response for Al3+ ions over a wide concentration range (2.0 x 10(-2) to 2.0 x 10(-6) M), with a limit of detection of 1.0 x 10(-6) M. It has a very fast response time of about 5 s and can be used for at least 3 months without any considerable divergence in the potentials. The proposed membrane sensor revealed very good selectivities for Al3+ over a wide variety of other metal ions, and could be used at a working pH range of 3.4 - 5.0. It was used as an indicator electrode in potentiometric titration of aluminum ions with EDTA, and in the determination of Al3+ in different real samples.     

Application of dopamine as an electroactive ligand for the determination of aluminum in biological fluids.

Dopamine (3,4-dihydroxyphenylethylamine, DA) is applied as an electroactive chelant for indirect determination of aluminum (Al) in biological fluids. It is observed that the decrease of the differential pulse voltammetric (DPV) anodic peak current of DA is linear with the increase of Al concentration. Under optimum experimental conditions (pH 8.6, 2.0 x 10(-4) M DA, and 0.03 M NH4Ac-NH3 x H2O buffer solution), two linear ranges, 5.0 x 10(-8) - 4.0 x 10(-7) M and 4.0 x 10(-7) - 7.2 x 10(-6) M Al(III), are obtained. The detection limit of Al is 1.9 x 10(-8) M and the relative standard deviation for 4 x 10(-6) M Al(III) is 3.1% (N = 8). Many biologically active foreign species have been selected for interference. Excellent recoveries and accuracy have been obtained in the measurements of Al in biological samples such as synthetic renal dialysate, Ringer's solution, human whole blood, cerebrospinal fluid of demented patient, and urine of diabetic patient. The methodological principle that Al complexes with DA on the electroactive position result in the depression of electrochemical activities of DA has been verified by comparing both the electrochemical behaviors and the spectroscopic responses like UV-vis and Raman of DA in the presence and in the absence of Al.     

Kinetic determination of trace cobalt(II) by visual autocatalytic indication

A highly sensitive and simple visual autocatalytic method has been developed for the determination of trace cobalt. The cobalt ion released by the oxidative decomposition of inert bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino-phenolato] cobaltate (Co(III)-5-Br-PAPS) with peroxomonosulfate acts as a catalyst for the oxidative degradation of the complex. Thus a definite time lapse of degradation is observed by the sudden disappearance of colored Co(III) complexes. The degradation time varies inversely with the logarithm of the initial concentration of cobalt(II). The determination range of cobalt(II) was from 3x10(-9) to 2x10(-7) M in the presence of 5x10(-6) M of 5-Br-PAPS. The relative standard deviation of the spot size method (10 mul) was 3.5% at 1x10(-7) M cobalt(II). This autocatalytic indicator reaction system has been successfully applied for the visual determination of urinary cobalt.     

Capillary electrophoretic determination of phosphate based on the formation of a Keggin-type [PMo12O40]3- complex.

Based on the formation of a Keggin-type [PMo12O40]3- complex, a sensitive capillary electrophoresis (CE) method was developed for the determination of P(V) with direct UV detection at 220 nm. A mixture of alpha- and beta-Keggin-type [PMo12O40]3- complexes was readily formed in a sample solution consisting of a trace amount of P(V), 2.5 mM Mo(VI), 0.050 M p-C6H3(CH3)-2-SO3H (XSA), and 60% v/v CH3CN. When a 0.05 M HCl and 60% v/v CH3CN solution was used as a migration electrolyte, the Keggin complexes exhibited a sharp and well-defined peak in the electropherogram. The peak area was linearly dependent on the P(V) concentration in the range of 5 x 10(-7)-5 x 10(-5) M; a detection limit of 1 x 10(-7) M was achieved. In comparison with indirect UV detection, the direct UV detection is about ten times more sensitive, because the Keggin complexes possess high molar absorptivities. The developed CE method was applied to the determination of P(V) in river water, and the results were in good agreement with those obtained by ion chromatography (IC) and colorimetry (COL) based on the formation of mixed-valence heteropoly blue species.     

Capillary electrophoretic determination of Ga(III) based on the formation of a heteropolyoxomolybdate complex

A novel capillary electrophoretic (CE) method was developed for the determination of Ga(III). The so-called Anderson-type [GaMo6O24H6]3- complex was readily formed by the reaction of Mo(VI) with Ga(III) in 0.050 M monochloroacetate buffer (pH 2.0) and the precolumn complex-formation reaction was applied to the CE determination of Ga(III) with direct UV detection at 240 nm. The peak area was linearly dependent on the concentration of Ga(III) in the range of 5.0 x 10(-7)-5.0 x 10(-5) M. Owing to the high molar absorptivity of the Anderson anion, a detection limit of 2.0 x 10(-7) M (signal-to-noise ratio=3) was achieved. The advantage of the present method is that the presence of large excesses of Al(III) and In(III) does not cause interference.     

Spectrofluorimetric determination of anthranilic acid derivatives based on terbium sensitized fluorescence.

Terbium sensitized fluorescence was used to develop a sensitive and simple spectrofluorimetric method for the determination of the anthranilic acid derivatives furosemide and mefenamic and tolfenamic acids. The method makes use of radiative energy transfer from anthranilates to terbium ions in alkaline methanolic solutions. Optimum conditions for the formation of the anthranilate-Tb3+ complexes were investigated. Under optimized conditions, the detection limits are 6 x 10(-9), 1.4 x 10(-8) and 9.0 x 10(-9) mol l-1 for furosemide, mefenamic acids and tolfenamic acid, respectively. The range of application is 2.5 x 10(-8)-5.0 x 10(-5) mol l-1 for all three drugs. The method was successfully applied to the determination of furosemide and mefenamic and tolfenamic acids in serum after extraction of the samples with ethyl acetate, evaporation of the organic layer under a stream of nitrogen at 40 degrees C and reconstitution of the residue with alkaline methanolic terbium solution prior to instrumental measurement. The mean recoveries from serum samples spiked with furosemide (5.0 x 10(-7), 2.0 x 10(-6) and 8.0 x 10(-6) mol l-1), mefenamic acid (3.0 x 10(-6), 9.0 x 10(-6) and 3.0 x 10(-5) mol l-1) and tolfenamic acid (3.1 x 10(-6), 12.5 x 10(-6) and 2.5 x 10(-5) mol l-1) were 96 +/- 8, 101 +/- 5 and 98 +/- 7%, respectively. The within-run precision (RSD) for the method for two serum samples of each drug varied from 2 to 8% and the day-to-day precision for two concentration levels varied from 2 to 13%.     

Determination of trace aluminum (III) using a novel cerium (IV)-calcein chemiluminescence detection

A simple, sensitive and selective chemiluminescence (CL) method was developed for the direct determination of aluminum (Al). This method is based on that the weak CL of cerium (IV)-calcein can be greatly enhanced by Al(III). The calibration curve was linear over the range 2.0 x 10(-10) to 4.0 x 10(-8)g mL(-1) with a detection limit of 8 x 10(-11)g mL(-1) (3sigma). The R.S.D. was 2.5% by 11 replicated determinations of 1.0 x 10(-9)g mL(-1) Al(III). The proposed method has been used to determine the concentration of Al(III) in real water samples with satisfactory results. The mechanism of the CL reaction was also discussed.     

Single-sweep polarography of the copper(II)-3-hydroxy-1-p-sulphonatophenyl-3-phenyltriazene complex and its analytical applications

A polarographic investigation of the copper-3-hydroxy-1-p-sulphonatophenyl-3-phenyltriazene (HSPT) complex in 0.05 M sodium tetraborate medium is described and a simple and sensitive single-sweep polarographic method for the determination of trace amounts of copper in biological samples is proposed. The complex was shown to be Cu(HSPT)2 with log beta' = 11.38. The polarographic wave is caused by the reduction of copper(II) in the adsorbed complex to copper amalgam on the surface of a mercury electrode. The current peak is directly proportional to the concentration of copper in the range 8.0 x 10(-9)-4.0 x 10(-6) M and the detection limit is 5.0 x 10(-9) M.     

Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates

A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples.     

Adsorptive stripping voltammetry for the determination of nifedipine in human serum

Adsorptive stripping voltammetry is used for the determination of trace levels of nifedipine. The conditions for preconcentration on the mercury drop electrode have been studied and the final measurements are made by differential pulse voltammetry. The response is linear from 2 x 10(-9) to 1 x 10(-7)M and can be extended to 10(-6)M by a change in conditions. The stripping peak has been used for determination of the drug in formulations, with a relative standard deviation of 0.8%. The method is applicable to the determination of nifedipine in blood-serum with a detection limit of 4.1 ng/ml.     

Simultaneous determination of phosphonate, phosphate, and diphosphate by capillary electrophoresis using in-capillary complexation with Mo(VI)

This study describes the simultaneous determination of phosphonate, phosphate, and diphosphate by CE with direct UV detection, based on in-capillary complexation with Mo(VI). When a mixture of phosphonate, phosphate, and diphosphate was injected into a capillary containing 3.0 mM Mo(VI), 0.05 M malonate buffer (pH 3.0) and 45% v/v CH3CN, three well-defined peaks, due to the migration of the corresponding polyoxomolybdate anions, were separated. The respective calibration graphs were linear in the concentration range of 2 x 10(-6)-2 x 10(-4) M for phosphonate, 1 x 10(-6)-5 x 10(-5) M for phosphate, and 1 x 10(-6)-2 x 10(-4) M for diphosphate; the correlation coefficients were better than 0.9990. The present CE method is successfully applied to the simultaneous determination of phosphonate, phosphate, and diphosphate in tap water.     

Enhanced spectrophotometric determination of nicotinic acid in a sodium dodecyl sulphate micellar medium

The spectrophotometric determination of pyridine and pyridine derivatives by means of the K?nig reaction was studied in micellar media of sodium dodecyl sulphate (SDS), N-cetylpyridinium chloride and Triton X-100. The sensitivity was largely increased in SDS micellar medium. The attack of the pyridine ring with cyanogen bromide to produce a glutaconic aldehyde was not affected by the presence of SDS, but the yield of the coupling reaction with an arylamine to produce a polymethine dye was largely increased. In the SDS micellar medium, aniline was superior to other coupling reagents. The limits of detection (LODs) were 6 x 10(-7), 1 x 10(-6) and 5 x 10(-7)M for pyridine, pyrrol-ylmethylpyridine and nicotinic acid, respectively, and the reproducibility for 2 x 10(-5)M solutions was ca. 2%. In the absence of SDS, the LODs were 3 x 10(-6), 3 x 10(-6) and 9 x 10(-6)M, respectively, and the reproducibility was ca. 3.5%. Application was made to the determination of nicotinic acid in pharmaceuticals.     

Spectrophotometric and spectrofluorometric determination of zinc and cadmium with 2,2'-pyridil bis(2-quinolylhydrazone)

The chelating ligand, 2,2'-pyridil bis(2-quinolylhydrazone), has been used for the spectrophotometric determination of zinc and cadmium in synthetic samples. The molar absorptivities of these metal complexes in 80% ethanol-water solution at pH 8 were found to be 4.60 x 10(4) and 5.10 x 10(4) 1.mole(-1).cm(-1) for zinc and cadmium respectively. Beer's law was obeyed for metal-ion concentrations between 1.0 x 10(-6) and 2.5 x 10(-5)M. The limits of detection were found to be 52 and 79 ng ml for zinc and cadmium respectively. The complexes fluoresced in 80% ethanol-water at pH 8 for zinc and at pH 10 for cadmium. The linear range for fluorescence as a function of metal-ion concentration was found to be 5 x 10(-7)-5 x 10(-6)M for both zinc and cadmium. Transition-metal ions interfere severely with both the spectrophotometric and fluorimetric determinations, and must be removed beforehand. An ion-exchange procedure is suitable for this.     

Determination of arsenate by sorption pre-concentration on polystyrene beads packed in a microfluidic device with chemiluminescence detection

A highly sensitive chemiluminescence (CL) method for the determination of arsenate in water based on a simple microfluidic device was developed. The method was based on sorption pre-concentration of arsenate as a form of vanadomolybdoarsenate heteropoly acid (VMoAs-HPA) ion-paired with hexadecyltrimethylammonium bromide on the surface of polystyrene beads packed in a microfluidic device monitored by chemiluminescence detection. The composition of the VMoAs-HPA complex was studied by varying the concentrations of ammonium molybdate, ammonium vanadate and sulfuric acid with a variable-size simplex optimization process, of which the optimum concentrations were 6.3 x 10(-5), 5.0 x 10(-6) and 1.0 x 10(-2) M, respectively. In this work, 1.0 x 10(-3) M ethylenediaminetetraacetic acid was added to all work solutions to remove the interferences of the other metal ions on the CL detection. The integration of sorption pre-concentration not only increased the detection sensitivity but also eliminated the interference from phosphate and chromate. The calibration plot was linear from 1.0 x 10(-7) to 5.0 x 10(-5) M As(v). The limit of detection was 8.9 x 10(-8) M As(v) (S/N = 3). The time required for one analysis run was as short as 5 min. The relative standard deviation was 5.9% (n = 9). This method was successfully applied to the determination of arsenate in mineral-, drinking- and tap-water samples.     

A new spectrofluorometric method for the determination of ascorbic acid based on its activating effect on a hemoglobin-catalyzed reaction.

A spectrofluorometric method for the determination of ascorbic acid (AA) based on its activation on the hemoglobin-catalyzed reaction was proposed. The fluorescence intensity of the product was measured under the optimal experimental conditions, i.e. 4.0 x 10(-6) M H2O2, 6.0 x 10(-5) M p-cresol, 1.2 M NH3-NH4Cl (pH 10.4) and 2.0 x 10(-7) M hemoglobin. The order of additions of the reagents was also studied. The activation of AA was found to be associated with a high ammonia concentration. The linear range of the method was 9.0 x 10(-10)-3.6 x 10(-8) M of AA. The detection limit was calculated to be 3.0 x 10(-10) M. The relative standard deviation of this method is 1.6% at 7.0 x 10(-9) M for 11 determinations.     

Optical detection of phenolic compounds based on the surface plasmon resonance band of Au nanoparticles

An indirect colorimetric method is presented for detection of trace amounts of hydroquinone (1), catechol (2) and pyrogallol (3). The reduction of AuCl4(-) to Gold nanoparticles (Au-NPs) by these phenolic compounds in the presence of cetyltrimethylammonium chloride (CTAC) produced very intense surface plasmon resonance peak of Au-NPs. The plasmon absorbance of Au-NPs allows the quantitative colorimetric detection of the phenolic compounds. The calibration curves derived from the changes in absorbance at lambda = 568 nm were linear with concentration of hydroquinone, catechol and pyrogallol in the range of 7.0 x 10(-7) to 1.0 x 10(-4)M, 6.0 x 10(-6) to 2.0 x 10(-4)M and 6.0 x 10(-7) to 1.0 x 10(-4)M, respectively. The detection limits were 5.3 x 10(-7), 2.5 x 10(-6) and 3.2 x 10(-7)M for the hydroquinone, catechol and pyrogallol, respectively. The method was applied satisfactorily to the determination of phenolic compounds in water samples and pharmaceutical formulations.     

Quantification of terbutaline in pharmaceutical formulation and human serum by adsorptive stripping voltammetry at a glassy carbon electrode

The electrochemical oxidative behavior of terbutaline at the glassy carbon electrode was studied in a series of the Britton-Robinson buffer of pH 2--11. Cyclic and square-wave voltammograms of terbutaline at the pH values 相似文献   

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10^-6 M. The concentration range is from 4.4 x 10^-6 to 3 x 10^-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10^-7 M. The concentration range is from 7 x 10^-7 to 6 x 10^-5 M. Iron(II) at concentrations as high asn x 10^-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.     

Differential pulse anodic stripping voltammetric determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone modified carbon paste electrode

A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters.