Search

Nalidixic acid, 7-hydroxymethylnalidixic acid, oxolinic acid, pipemidic acid and cinoxacine form complexes with zinc(II) in the presence of acetate buffer of pH 5.5 and oxolinic acid, pipemidic acid and cinoxacine form complexes with aluminium(III) in the presence of chloroacetate buffer of pH 3.0. In all cases, an enhancement of the fluorescence emission was observed. Fluorimetric studies on the spectral characteristics of the complexes were performed. A 1:1 stoichiometry for all the complexes was established. The association constants were calculated, by using the changes in the fluorescence of all antibacterials, that occurred when the complexes were formed. The fluorescence reactions were used to develop methods for the determination of all of the above compounds, showing a higher sensitivity than in the absence of the cationic ions. The methods were satisfactorily applied to the determination of these compounds in urine.

Three multivariate calibration methods, partial least squares (PLS-1 and PLS-2) and principal component regression (PCR), were applied to the simultaneous determination of three flavour enhancers (inosine 5'-monophosphate, guanosine 5'-monophosphate and monosodium glutamate), in mixtures by ultraviolet/visible absorption spectrophotometry. The absorption and first- and second-derivative absorption spectra of the ternary mixtures were used to perform the optimization of the calibration matrices by the PLS and PCR methods. The results obtained by the application of the different chemometric approaches are discussed and compared. No significant advantages were found for the prior differentiation step. The proposed method was applied satisfactorily to the determination of inosine 5'-monophosphate and guanosine 5'-monophosphate in several food preparations, in the presence of monosodium glutamate.

The simultaneous determination of salicylic acid in binary and/or ternary mixtures and its two main urinary metabolites is proposed. Mixtures of salicylic, salicyluric and gentisic acids are resolved by synchronous spectrofluorimetry, in combination with first-derivative measurements. The urine is extracted with diethyl ether in acid medium. Salicylic and salicyluric acids are re-extracted into glycine-sodium hydroxide buffer solution of pH 11.6 and determined at that pH, and salicylic and gentisic acids are re-extracted into boric acid-sodium hydroxide buffer solution of pH 8.5 and determined at pH 6.