M. Hernandez Lopez

Fluorimetric determination of scandium using the cyclodextrin-1,4-dihydroxyanthraquinone inclusion complex

Quinizarin (1,4-dihydroxyanthraquinone) and β-cyclodextrin (β-CD) form a 1 : 1 inclusion complex with an estimated association constant of 200 l mol–1 at pH 7.1. The hydrophobic nature of β-CD helps to dissolve and stabilise the dye and hence permits its use as a ligand in coordination reactions with metal ions. This inclusion compound has been used for the fluorimetric determination of trace amounts of scandium. A limit of detection of < 1 ng ml–1 of scandium was obtained with a relative standard deviation of 5%. The method was free from interferences from 40 species tested at concentration ratios below 1 : 1 m/m.

Enhanced fluorimetric determination of procaine in pharmaceutical preparations by aqueous β- cyclodextrin inclusion and non-aqueous competitive action

Abstract The effects of changes in polarity and dielectric constant of the solvent on the fluorescence of procaine hydrochloride in different solvents, and in β-cyclodextrin (β-CD) and micellar media (cetylpyridium chloride and sodium dodecyl sulphate), are described in detail. It is shown that, with N,N -dimethylformamide as solvent procaine is better incorporated in β-CD and micelles. Methods are developed under these conditions based on normal, synchronous first- and second- derivative fluorimetry. The linear dynamic range is 10–680 ng ml -1 and the detection limit is 2.5 ng ml -1 ; the relative standard deviation is 0.68% for the β-CD method with normal fluorimetry. The methods are applied directly to the determination of procaine in different pharmaceutical preparation with recoveries of 88–108%.

Spectrofluorimetric determination of beryllium based on the inclusion complex of 1-amino-4-hydroxyanthraquinone with β-cyclodextrin as ligand

Abstract The use of the inclusion complex of 1-amino-4-hydroxyanthraquinone (AHA) in the internal cavity of β-cyclodextrin is compared with AHA alone as a ligand for the spectrofluorimetric determination of beryllium. The organizing ability of the cyclodextrin medium and the protection of the ligand from the micro-environment confers increased sensitivity, selectivity and detection limit, and allows the determination of 10–70 ng ml−1 beryllium, compared to 60–500 ng ml−1 in the absence of the cyclodextrin.

A graphical derivative approach to the photometric determination of lutetium and praseodymium in mixtures

The reaction of lanthanides with 1,4-dihydroxyanthraquinone has been examined and optimum conditions have been found for the separate spectrophotometric determination of Lu and Pr. A graphical method based on use of first and second derivative spectra has been developed for analysis of binary mixtures of the two, in concentration ratios from 1:5 to 5:1. Linear calibration curves were obtained between 1 and 10 mug/ml.

Three-dimensional synchronous fluorimetric determination of indole-type auxins after derivatization with o-phthalaldehyde

Abstract A sensitive fluorimetric method for teh determination of indole-derivative plant-growth regulators of the auxin group (indole-3-acetic acid, indole-3-butyric acid and indole-3-propanoic acid) is based on their eaction with o -phthaladehyde in concentrated sulphuric acid. The fluorescence spectra of the three derivatives are very similar, but the advantages offered by a three-dimensional plot of the spectra, the synchronous derivative approach and the optimization of experimental variables permit the individual and simultaneous quantitation of mixtures of these compounds at the ng ml -1 level.

Isodifferential derivative approach to the spectrophotometric determination of nickel and cobalt mixtures

Abstract A graphical method for measuring derivative amplitudes in binary mixtures with overlapping spectra is described. The method is based on the interference-free character of the isodifferential points in the derivative calibration graphs. Cobalt and nickel mixtures are analyzed in the range 0.01–2.5 μg ml−1 by the formation of coloured chelates with benzyl-2-pyridylketone 2-pyridylhydrazone, with relative standard deviations ⩽1.5%.

Trace zinc determination by synchronous derivative fluorimetry

A sensitive and selective synchronous-scanning derivative spectrofluorimetric determination of zinc based on the formation of a fluorescent chelate with 2-furaldehyde 2-pyridylhydrazone (FAPH) is described, and its analytical performance compared with that of the ordinary fluorimetric method. The detection limits lie in the ng ml range and the coefficient of variation is below 2% in both cases. The methods have been applied to the trace determination of zinc in pig liver tissue and environmental fume samples.

Isodifferential derivative synchronous fluorimetric approach for the determination of gallium and aluminium in mixtures

Abstract This study was designed to test the feasibility of determining two substances in a mixture, when each has nearly the same spectral shape, by taking advantage of the special interference free character of the isodifferential point in the first derivative calibration graph. The research reported here describes a method of measuring derivative amplitudes in binary mixtures with superimposed spectral shapes. The fundamental theoretical aspects of the methodology are discussed. Aluminium and gallium oxinates, which have nearly the same broad, structureless, fluorescence spectra in a water—ethanol medium (40:60) (v/v) at pH 6.60, have been analysed with moderate success by applying synchronous derivative fluorimetry.

Simultaneous determination of vanillin and syringaldehyde in rum by derivative spectrophotometry

A derivative spectrophotometric procedure for the simultaneous determination of vanillin (4-hydroxy-3-methoxybenzaldehyde) and syringaldehyde (4-hydroxy-3,5-dimethoxybenzaldehyde) in rum is described. The method minimises the mutual interference between vanillin and syringaldehyde and allows the determination of these compounds without a previous extraction step. The precision of the method, expressed as the relative standard deviation, is better than 4%.

Spectrofluorimetric determination of the organophosphorus insecticide quinalphos in citrus fruits

Abstract The simple spectrofluorimetric method described for the determination of quinalphos in citrus fruits has a limit of detection of 3 ng ml −1 . The extracted insecticide is weakly fluorescent and is hydrolyzed in alkaline medium to give the strongly fluorescent quinoxalin-2-ol. Factors affecting the rate of hydrolysis are described in detail. Methods are developed based on normal and synchronous spectrofluorimetry. Recoveries are in the range 95–99% with relative standard deviations 2.5-4%. The method is suitable for determining quinalphos in spiked citrus fruit. The proposed method is compared with a liquid-chromatographic method.