Biomedical subjects
Publications and source records attributed to J L Vilchez.
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A method for the simultaneous determination of the colorants Sunset Yellow FCF and Quinoline Yellow using solid-phase spectrophotometry is proposed. The colorants were isolated in Sephadex DEAE A-25 gel at pH 5.0, the gel-colorants system was packed in a 1 mm silica cell and spectra were recorded between 400 and 600 nm against a blank. Statistical results were obtained by partial least squares (PLS) multivariate calibration. The optimized matrix by using the PLS-2 method enables the determination of the colorants in artificial mixtures and commercial soft drinks.
A spectrofluorimetric method for the determination of paracetamol is presented, based on the oxidation of the analyte to give the fluorophore 2,2'-dihydroxy-5,5'-diacetyldiaminebiphenyl. Sodium hypochlorite was used as an oxidizing reagent and the optimum pH was found to be 10.0 (sodium carbonate-boric acid buffer solution). The linear concentration range of application was 0.1-100.0 micrograms ml-1 of paracetamol, the detection limit 0.01 micrograms ml-1 and the relative standard deviation 1.2%. The method has been satisfactorily applied to the determination of paracetamol in pharmaceutical formulations and biological fluids.
A simple and sensitive method is proposed for the determination of boldine by first-derivative synchronous spectrofluorimetry based on its native fluorescence in 0.1 N sulphuric acid. The constant wavelength difference (delta lambda = lambda em--lambda ex) chosen to optimize the determination is 90 nm. The linear concentration range of application is between 2.0 and 50.0 micrograms l-1 of boldine, the detection limit 0.4 microgram l-1 and the relative standard deviation at a concentration of 25 microgram l-1 was 2.1%. The method has been satisfactorily applied to the determination of boldine in pharmaceutical formulations.
A new, sensitive and simple spectrofluorometric method for the determination of thiabendazole (TBZ) residues was studied. TBZ on Sephadex G-15 gel, pH 4.70 acetate buffer, is fixed to give fluorescence. The fluorescence of the gel-TBZ system, packed in a 1-mm quartz cell was measured directly using a solid-surface attachment. The applicable concentration range was 1.5-10.0 ng.mL-1 with a relative standard deviation of 1.4% and a detection limit of 0.1 ng.mL-1. The method was applied to the determination of thiabendazole in natural, waste, sea, and residual waters (98-100% recovery). The method is more sensitive and selective than other methods described in the literature. The presence of other fluorescent pesticides (dichlone, carbaryl, morestan, o-phenylphenol) with similar spectral features (lambda exc and lambda em neighboring to excitation and emission wavelengths of the TBZ) did not cause interference.
An analytical procedure for determination of thiabendazole (TBZ) residues in pears is described. The method involves extracting the chemical from the chopped fruit with buffer solution (acetic acidacetate, pH 4.6), use of Sephadex G-15 dextrantype gel as a solid support, and determination of TBZ by solid-phase spectrofluorimetry (SPF). The relative fluorescence intensity of the Sephadex G-15 gel-TBZ system, packed in a 1 mm-thickness silica cell, was measured directly at lambda ex = 303 nm and lambda em = 350 nm with a solid-phase attachment. The applicable concentration range was 5.0-20.0 ppb with a detection limit of 0.5 ppb. Recoveries were from 98.7 to 102.0% when 15.0 ppb of TBZ was added to the fruit.