Flow-injection determination of europium after on-line reduction

A zinc reductor minicolumn is used in a flow-injection system for reduction of europium(III) to europium(II). Europium(II) is indirectly determined either spectrophotometrically by oxidation with iron(III) and reaction of the iron(II) formed with 1,10- phenanthroline, or spectrofluorimetrically by reaction with cerium(IV) and measurement of the cerium(III) produced. The reductor functions efficiently at flow rates up to 1 ml min^?1, which allows sample injection rates up to 100 h^?1. Linear calibration is achieved for 10–200 and 0.5–4 μg ml^?1 with detection limits of 2.5 and 0.25 μg ml^?1, by spectrophotometry and spectrofluorimetry, respectively.     

Low-Temperature Phosphorescence Analysis of Mebendazole and Related Imidazoles

Abstract

Native low-temperature phosphorescence of mebendazole and flubendazole in ethanol is used for the determination of these imidazoles in anthelmintic preparations with wavelength maxima and detection limits of λ_EXC = 322 nm, λ_EM = 454 nm; 10 ng ml^?1 and λ_EXC = 325 nm, = λ_EM = 455 nm; 5 ng ml^?1, respectively, with linear response up to 8 μg ml^?1 and 9 μg ml^?1, respectively. The structural basis of these phenomena is discussed for both compounds and for related imidazoles and benzimidazoles. Apart from good sensitivity and excellent specificity offered by the technique, the use of cryogenic equipment (liquid nitrogen, special cuvettes, expensive dewar cells) implies some disadvantages for routine analyses.     

Molekülabsorptionsspektrometrie bei elektrothermischer verdampfung in einer graphitrohrküvette: Teil 7. Untersuchung der erdalkali-halogen-molekülabsorptionen,bestimmung von Fluorid- und Chloridspuren durch die molekülabsorption von MgF- und MgCl-molekülen

(Molecular absorption spectrometry with electrothermal volatilization in a graphite tube. Part 7. A study of molecular absorption of alkaline earth halides and determination of traces of fluoride and chloride based on molecular absorption of MgF and MgCl moleculesv)The molecular absorption of alkaline earth halides, generated by volatilization in a normal graphite tube, is reported. Intense absorption bands were found only with MgF and MgCl molecules. These molecules are used for the determination of fluoride and chloride, respectively. Fluoride can be determined at 268.3 nm or 358.2 nm; for 10-μl injections, the linear ranges are, respectively, 0–6 μg ml^-1 and 0–35 μg ml^-1, with sensitivities (0.01 absorbance) of 2.4 ng and 7.5 ng. Chloride can be determined at 376.3 nm; response is linear up to 15 μg ml^-1, with a sensitivity of 5.8 ng if copper ions are added. Optimal conditions, interferences and mechanisms are discussed.     

High-Performance Liquid Chromatographic Assay for Chlorquine and its Two Major Metabolites,Desethylchloroquine and Bidesethylchloroquine in Biological Fluids

Abstract

A high-performance liquid chromatography (HPLC) method for the determination of chloroquine and its two major metabolites in biological fluids is described. Hydroxychloroquine is used as an internal standard (I.S.). Drug, metabolites and I.S. were extracted as bases with diethyl ether by a single step procedure. After drying and evaporation of the organic phase, the residue was dissolved into the mobile phase and injected into the chromatographic system. Separation was performed using a normal phase column (Inertsil sill with mixture of acetonitrile, methanol and ammonia as mobile phase. The detection was carried out by fluorescence measurement : excitation wavelength was set at 325 nm and emission at 380 nm. The limit of detection was near 3.7 ng ml^?1 for chloroquine and metabolites. No chromatographic interference could be detected by endogenous compounds or other antimalarial drugs. Because of the good accuracy of the method, concentrations were determinated with a relative standard deviation lower than 7% at the 25 ng ml^?l level for all substances.

An excellent precision was obtained over the range of concentrations tested, 25–1000ng ml^?l. This method can be applied to therapeutic, pharmacokinetic and epidemial studies.     

Flow injection spectrophotometric determination of europium using chlortetracycline

A flow injection (FI) spectrophotometric determination of europium (III) is described, based on the complexation between europium (III), and chlortetracycline (CTC) in a Tris-buffer pH 8.0 medium. The resulting yellow-coloured complex is measured at its absorption maximum of 400 nm after 100 μl of sample or standard solution containing europium (III) are injected into the merged streams of CTC and Tris-buffer solutions. Optimum conditions for determining μg amounts of europium (III) are achieved by univariate method. Various types of reactors are also investigated. It is shown that the use of a single bead string reactor gives rise to the enhancement of peak height. A linear calibration curve over the range of 0.10-0.60 μg ml⁻¹ europium (III) is established with the regression equation (n=6) Y=34.93X+0.01 and the correlation coefficient of 0.9994 is obtained. A detection limit (3σ) of 0.01 μg ml⁻¹ of europium (III) and the relative standard deviation (R.S.D.) of 4.32% for determining 1.0 μg ml⁻¹ of europium (III) (n=7) are obtained. The recommended method has been applied to the quantitation of europium (III) in spiked water and stream sediment samples with average recoveries of 99.9 and 97.5%, respectively. The sampling rate is found to be 85 h⁻¹.     

2-(α-pyridyl)thioquinaldinamide: a novel fluorimetric reagent in inorganic trace analysis. : Part 2. A simple selective determination of selenium(IV) at Ultratrace Levels

The very sensitive fluorimetric determination of selenium(IV) is based on its oxidation of the non-fluorescent 2-(α-pyridyl)thioquinaldinamide in slightly acidic solution (0.05–0.15 M sulphuric acid). The excitation and emission wavelengths are 350 nm and 500 nm, respectively. Linear calibration graphs are obtained for different ranges of selenium concentration between 0.01 ng ml^?1 and 0.5 μg ml^?1. Over sixty ions either do not interfere or can be masked in the determination of 1 ng ml^?1 Se(IV). The method is applied successfully to various synthetic mixtures and to a native sulphur sample. The reaction is fast and the fluorescent system is stable for 24 hours.     

Determination of chloramphenicol at ultra-trace levels by high-performance differential pulse polarography: Application to Milk and Meat

High-performance differential pulse polarography (h.p.d.p.p.) is used to determine the antibiotic chloramphenicol. Optimum operating conditions are discussed. Calibration curves are linear from 10 ng ml^-1 to 1 μg ml^-1; the detection limit is about 3 ng ml^-1. Above 1 μg ml^-1, deviations from linearity occur, because of adsorption of chloramphenicol at the mercury electrode. A correction, based on variations in natural drop time, is suggested. Chloramphenicol is readily extracted from milk or minced meat with diethyl ether. The ether is evaporated, and the residue is taken up in acetate buffer pH 4.7 and filtered through a membrane filter. Recoveries from samples fortified at levels of 10–1000 ng ml^-1 are about 60% for milk and 50% for minced meat.     

Sorption of arsenic,antimony and bismuth on glycolmethacrylate gels with bound thiol groups for direct sampling in electrothermal atomic absorption spectrometry

Batch sorption of arsenic, antimony and bismuth from solutions in 1 M sulphuric acid has distribution coefficients of 10⁴–10⁵. Quantitative sorption on the hydrophilic methacrylate gel containing thiol groups (Spheron Thiol) is possible within 60 min for bismuth or arsenic and 120 min for antimony. Conditions for the electrothermal atomization of arsenic sorbed on Spheron Thiol and injected into the graphite tube as a suspension are optimized. The sensitivities possible are 3.2 ng As ml^-1, 13 ng Sb ml^-1 and 2.8 ng Bi ml^-1; the coefficient of variation for 10 ng of As is 4%. Complete recovery of 40 ng As ml^-1 added to solutions of 5% KCI or 5% MgCl₂ and to river water was obtained.     

Fluorimetric determination of magnesium by ternary complex formation with pyridoxal nicotinylhydrazone and amines

The synthesis, characteristics and analytical applications of pyridoxal nicotinylhydrazone are described. This compound reacts with magnesium(II) in the presence of ammonia, ethylenediamine or pyridine, to produce a 1:1:1 Mg(II)—pyridoxal nicotinylhydrazone—amine fluorescent complex (λ_ex 395 nm, λ_em 480 nm). A fluorimetric method is proposed for the determination of magnesium(II) (20–100 ng ml^-1 in the solution measured); isobutanol is used to extract the complex, reducing the number of interferences.     

Determination of manganese with triethanolamine and o-tolidine by conventional and long-path photometry

A very sensitive method for the spectrophotometric determination of manganese is reported. To the sample is added triethanolamine (TEA) and sodium hydroxide to give a pH above 11; after atmospheric oxidation of manganese(II) to the green manganese(III)—TEA complex, sodium pyrophosphate is added and the solution is acidified. Manganese(III) thus forms a complex with pyrophosphate. Then o-tolidine is added and is oxidized in a 2e step to the intensely yellow quinonediimine, while manganese(III) is reduced to manganese(II). The absorbance is measured at 440 nm. The calibration curve is linear up to 1.6 μg Mn ml^-1 in the final solution; the limit of determination is 0.2 μg Mn ml^-1. For the 20-cm path cell, the respective data are 45 ng Mn ml^-1 and 2 ng Mn ml^-1. The only severe interferences are strong oxidants like dichromate or cerium(IV), which are readily reduced with sulfurous acid. Vanadium in amounts up to 2–3 times that of manganese can be dealt with by an appropriate blank solution; larger amounts of vanadium must be removed e.g. by a cupferron extraction.     

A simple and sensitive continuous hydride generation system for the determination of arsenic and selenium by atomic absorption and atomic fluorescence spectrometry

The development and optimization of a continuous hydride generation system for atomic absorption spectrometry (a.a.s.) and atomic fluorescence spectrometry (a.f.s.) is described. Sodium tetrahydroborate(III) solution and sample solution are delivered by two small peristaltic pumps to a gas/liquid separator. The evolved hydrides are swept to a miniature argon/hydrogen diffusion flame burning on a borosilicate glass tube. Detection limits (2σ) obtained for arsenic are 0.8 ng ml^-1 by a.a.s. and 0.34 ng ml^-1 by a.f.s., and for selenium 0.5 ng ml^-1 by a.a.s. and 0.13 ng ml^-1 by a.f.s. Linear working ranges are typically 1–100 ng ml^-1 with a typical measurement time of 1 min per sample or standard.     

Time discrimination in the laser fluorimetry and ultratrace determination of europium(III) and samarium(III) with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione

Efficient application of time discrimination has succeeded in substantial reduction of the detection limit of laser fluorimetry. A nitrogen laser and a pulse-gated photon counting method are combined. The detection limits for europiuni(III) and samarium(III) with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione in solution are 0.4 pg l^-1 and 0.3 ng l^-1, respectively. The results are attributed to effective removal of the short-lived unwanted signals. This technique makes possible the ultratrace determination of a fluorescent molecule in a mixture with others by making the most of the difference of their emission lifetimes. The europium(III) complex can be determined with high selectivity and sensitivity in a large excess of the samarium(III) complex     

Flow Injection Catalytic Determination of Vanadium using the Indicator Reaction between Victoria Blue B and Bromate and A Citric Acid Activator

ABSTRACT

A flow injection catalytic method is proposed for determination of trace vanadium based on its catalytic action on a new indicator reaction between Victoria blue B (VBB) and potassium bromate in the presence of citric acid as an activator and in dilute sulfuric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of VBB injected at the maximum absorption wavelength of 618 nm. The detection limit is 0.5 ng ml^?1 and is independent of the initial valence state of vanadium. The relative standard deviation is 1.5% obtained from 11 standard solutions each containing 40 ng ml^?1 of vanadium. The sampling rate is about 15 samples per hour. This method is very simple and has been applied to the determination of trace vanadium in some natural waters with recoveries of 93-103%.     

Fluorimetric determination of chromium at low levels with 3-hydroxyflavone and application of the method to steels

The method is based on a 1:1 Cr(VI)/3-hydroxyflavone complex which is extracted into benzene at H_o = ?0.6. The complex has a pK^* value of 7.8 ± 0.1. Chromium is determined in the range 10–650 ng ml^?1 with excitation at 358 nm and emission measurement at 530 nm. The relative standard deviation is 6.1% for 332 ng ml^?1 chromium (n = 10). The method is applied to the determination of chromium in steels.     

Synthesis and luminescence properties of new red-shifted absorption lanthanide(III) chelates suitable for peptide and protein labelling

The synthesis and photo-physical properties of an original bis-pyridinylpyrazine chromophore efficiently sensitising europium(III) and samarium(III) are described. The corresponding lanthanide(III) complexes display in aqueous solutions a maximum excitation wavelength which is significantly red-shifted compared to the usual terpyridine-based chelates, and a valuable luminescence brightness above 2,000 dm(3) mol(-1) cm(-1) at 345 nm was obtained with a europium(III) derivative. Further functionalisation with three different bioconjugatable handles was also investigated and their ability to efficiently label a model hexapeptide was evaluated and compared. Finally, the best bioconjugatable europium(III) chelate was used in representative labelling experiments involving monoclonal antibodies and the luminescence features of the corresponding bioconjugates remained satisfactory.     

The application of the ph-stat method to metal ion-catalyzed reactions

The pH-stat method, which is well known in organic chemistry and biochemistry, is used for the kinetic determination of metal ion catalysts. Indicator reactions that involve protons can be followed by controlled addition of standard base or acid. This is illustrated by the following examples: determination of copper(II) (0.03–0.3 μg ml^-1) with the indicator reaction ascorbic acid—peroxydisulphate; determination of molybdenum(VI) (0.2–2.5 μg ml^-1) with the indicator reaction thiosulphate—hydrogen peroxide; determination of zirconium(IV) (0.2–2 μg ml^-1) with the indicator reaction iodide—hydrogen peroxide; and determination of vanadium(V) (0.2–2 μg ml^-1) with the indicator reaction iodide—bromate. For one example, the copper—ascorbic acid—peroxydisulphate reaction, it is shown that the pH-stat method has distinct advantages over closed systems, giving considerably better sensitivity for the determination of copper (0.5–5 ng ml^-1 ).     

Determination of zinc and cadmium by flow injection analysis and chemiluminescence

Zinc (10–100 ng ml^-1 and cadmium (20–200 ng ml^-1) are successively eluted from an ion-exchange column and determined by their inhibition of the cobalt-catalyzed chemiluminescence generation from luminol.     

Spectrofluorimetric determination of titanium,zirconium and hafnium and their binary mixtures with biacetylmonoxime nicotinylhydrazone

The synthesis, characteristics and analytical applications of biacetylmonoxime nicotinylhydrazone are described. This compound forms fluorescent complexes with titanium(IV) (λ_ex = 430, λ_em = 540 nm), zirconium (λ_ex = 415 nm, λ_em = 505 nm) and hafnium (λ_ex = 400, λ_em = 500 nm) in an acidic medium. Titanium forms a 1:2 metal:ligand complex, whereas zirconium and hafnium form 1:2:1 metal:ligand:sulphate ternary complexes. Highly selective spectrofluorimetric methods for titanium (20–100 ng ml^?1), zirconium and hafnium (5–100 ng ml^?1) are proposed, and procedures for the analysis of binary mixtures of these ions are described.     

Determination of traces of gallium in the presence of aluminium by synchronous derivative spectrofluorimetry

Gallium (2–100 ng ml^?1) is determined in the presence of ?500-fold amounts (by weight) of aluminium by using synchronous first- or second-derivative spectrofluorimetry. The fluorescence of the gallium chelate with 1-(2-pyridylazo)-2-naphthol is greatly enhanced compared to that of the aluminium chelate in micellar sodium dodecyl sulphate solutions. The limit of detection is about 0.6 ng ml^?1.     

The europium/samarium-2-benzoyl-indane-1,3-dione-cetyltrimethylammonium bromide fluorescence system and its analytical application

The fluorescence system of the Eu³⁺ (or/and Sm³⁺)-2-benzoyl-indane-1,3-dione(BID)-cetyltrimethylammonium bromide (CTMAB) was investigated at excitation wavelengths of 350 nm, and emission wavelengths at 612 nm for europium and 565, 606 and 650 nm for samarium, respectively. The system was used for the determination of Eu and Sm in rare earth oxides and of BID in water. Europium or/and samarium could be determined in the range of 1.0 × 10^–9–1.0 × 10^–5 mol/L and 2.0 × 10^–8–5.0 × 10^–5 mol/L, respectively; 1.0 × 10^–6–2.0 × 10^–5 mol/L of BID could also be determined. Received: 5 March 1997 / Revised: 6 August 1997 / Accepted: 20 September 1997