Francisco Salinas López

Abilities of differentiation and partial least squares methods in the analysis by differential pulse polarography Simultaneous determination of furazolidone and furaltadone

Abstract A comparison between the applicability of two multicomponent analysis methods, differentiation of signals and partial least squares (PLS) methods, to the resolution of overlapping differential pulse polarographic (DPP) peaks corresponding to the irreversible reduction process of two nitrofuran derivatives has been performed. The results show that the derivative DPP signals are not suitable for the resolution of mixtures of these system, by application of the zero-crossing method, because the zero-crossing potential is not independent of the concentration. However, PLS has the capacity of modelling the total evolution of the DPP peaks with the concentration. The PLS multivariate calibration method has been successfully applied to the simultaneous analysis of both compounds in a pharmaceutical formulation.

Resolution of ternary mixtures of nitrofurantoin, furazolidone and furaltadone by application of Partial Least Squares analysis to the differential pulse polarographic signals

The abilities of the Partial Least Squares (PLS) methods in the resolution of ternary mixtures of organic compounds (furaltadone, furazolidone and nitrofurantoin) by using their differential pulse polarographic (DPP) signals are reported. The applicability of these methods to resolve very overlapped peaks whose E(p) also changes with concentration is demonstrated. The analysis of both synthetic and real samples has been made with satisfactory results. The relative error of prediction (REP) is 8.7% for FD, 7.7% for FZ and 6.7% for NF by application of the PLS-2 method.

Simultaneous fluorometric determination of nalidixic acid and 7-hydroxymethylnalidixic acid by partial least squares calibration

Abstract The resolution of binary mixtures of nalidixic acid (NA) and 7-hydroxymethylnalidixic acid (OH–NA) has been accomplished by partial least squares (PLS) and principal component regression (PCR) multivariate calibration. The method of determination is based on the fluorescence emission of these compounds in the presence of γ-cyclodextrin (γ-CD). The formation of the inclusion compounds gives rise to an increase of the fluorescence emission compared to aqueous solution. The total luminescence information of the compounds has been used to optimize the spectral data set to perform the calibration. A comparison between the predictive ability of three multivariate calibration methods, PLS-1, PLS-2 and PCR, on three spectral data sets, excitation, emission and synchronous spectra has been performed. The PLS-1 method, applied to the emission spectra, has been selected as optimum. The proposed method has been applied to the simultaneous determination of NA and OH–NA in urine. Recovery values from urine samples containing (NA) and (OH–NA) range from 91 to 103% (mean 97%), and from 92 to 105% (mean 99%), respectively.

Complexation of antibacterial quinolonic acid and cinolonic derivatives with Zn(II) and Al(III): application to their determination in human urine.

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.

Simultaneous kinetic spectrophotometric determination of 2-furfuraldehyde and 5-hydroxymethyl-2-furfuraldehyde by application of a modified Winkler's method and partial least squares calibration

A method is described for the simultaneous determination of 2-furfuraldehyde and 5-hydroxymethyl-2-furfuraldehyde, based on their reaction by a modified Winklers method. A comparative study of the results found using the kinetic curves registered at 550 and 585 nm, as analytical signals, has been performed. The data set of the kinetic curves at 550 nm was selected as the analytical signal. Partial least squares (calibrating for a single chemical constituent at a time: PLS-1) multivariate calibration was then applied for the determination. The proposed method was satisfactorily applied to the analysis of wines, spirits, fruit juices and honey.

Kinetic fluorimetric study of the oxidation reaction of folinic acid (leucovorin) with potassium permanganate. Determination in human urine

In this study a kinetic fluorimetric method for the determination of folinic acid (leucovorin, LV) in human urine has been developed. The fluorescence emission generated by the oxidation reaction between LV and potassium permanganate in alkaline medium has been monitored at 360nm (excitation wavelength 290nm). The effect of instrumental and experimental variables on the reaction was investigated and a 0.17M sodium hydroxide, 3.3x10(-5)M KMnO(4) concentration and a temperature of 70 degrees C were selected for the reaction. The concentration range has been optimized between 10 and 700ngml(-1) of LV. The correlation coefficient was 0.9989. The sensitivity of the proposed method is 9.5ngml(-1) (expressed as limit of detection in accordance with the Clayton criterion). The determination time per sample is smaller than 200s. The proposed kinetic fluorimetric method has been applied to the direct determination of this compound in human urine. Recovery values from urine samples, containing LV, range from 82 to 110% (mean 96%).

Kinetic behaviour of the malonaldehyde-thiobarbituric acid reaction. Kinetic-fluorimetric determination of malonaldehyde in human serum

Abstract For the first time a fluorimetric-kinetic method for the determination of malonaldehyde (MLD) is proposed. The fluorescence emission of the thiobarbituric acid (TBA)-MLD reaction product has been monitored at 553 nm (excitation wavelength 515 nm), and the instrumental and experimental variables have been studied. A selective and fast kinetic-fluorimetric determination of malonaldehyde is proposed. The sensitivity of the method is very high, the detection limit is 0.30 ng ml −1 , the application range is between 1.1 and 50 ng ml −1 , and the determination time per sample is 500 s. The kinetic-fluorimetric method has been applied in the determination of two types of pathological human serum: rheumatic and hyperlipemic serum. In both cases, perchloric acid is used to precipitate the proteins.

Square wave adsorptive stripping voltammetric determination of piromidic acid. Application in urine

Abstract A simple procedure for the determination of piromidic acid by square wave adsorptive stripping voltammetry (SW-AdSV) at a hanging mercury drop electrode has been developed. The variables affecting to accumulation process such as concentration of perchloric acid, accumulation potential and accumulation time have been optimised (0.025 mol L−1, −0.25 V and 140 s, respectively) by using response surface methodology. A linear relationship between concentration of piromidic acid and peak intensity has been found in the range 2.22×10−9 to 3.33×10−8 mol L−1. The detection limit (1.65×10−9 mol L−1) has been calculated by the method proposed by Clayton et al. so that protection against both false positive and false negative errors is assured. The procedure was successfully applied to determine piromidic acid in spiked urine samples. The obtained recovery values were in the range 97.3–103.3% at different levels of concentration of piromidic acid.