Juana Rodriguez Flores - Academia.edu (original) (raw)

Papers by Juana Rodriguez Flores

American Journal of Analytical Chemistry, 2011

This work presents a multi-residue analytical method based on solid phase extraction (SPE) follow... more This work presents a multi-residue analytical method based on solid phase extraction (SPE) followed by high-performance liquid chromatographic (HPLC) with diode array (DAD) detection for the simultaneous determination of a group of pharmaceutical products that include ten antidepressants and three anticancerigenic in environmental samples (water and soil). Baseline separation of the studied compounds was obtained on an ultrabase C 18 (4.6 mm i.d. × 150 mm, 5 μm particle) column using acetonitrile:phosphate buffer pH 2.5 (35:65, v/v) as mobile phase with a flow rate of 1.5 mL/min. Different aspects including linearity, accuracy, precision and detection and quantification limits were examined in order to validate the proposed method. Detection limits between 1 and 50 ng/mL were obtained for all the target compounds. This method was applied to the analysis of environmental samples as waters and soils of different precedence. Prior, the HPLC determination the samples were purified and enriched using SPE or liquid-liquid extraction (LLE) of the target compounds.

Analytical Letters, 1992

Abstract A new method for determining the binary mixtures of procaine penicillin G and benzathine... more Abstract A new method for determining the binary mixtures of procaine penicillin G and benzathine penicillin G using zero-crossing second derivative spectrophotometry is described. Calibration graphs were linear up to 8.80 10− 5 M for procaine penicillin G and ...

Analytical Letters, 1989

Abstract The electroanalytical anodic behaviour of orotic acid has been studied at several pH val... more Abstract The electroanalytical anodic behaviour of orotic acid has been studied at several pH values, using DPP and CV techniques. The orotic acid undergoes an anodic wave in both techniques. The best conditions for the determination of orotic acid with the mentioned techniques was studied. The determination of Hg(II) by classic polarography, DC, was performed.

Analytica Chimica Acta, 2004

Development of a capillary gas chromatographic method with flame ionisation detection for the sim... more Development of a capillary gas chromatographic method with flame ionisation detection for the simultaneous determination of sildenafil and its N-demethylated metabolite in biological fluids A simple, rapid, and sensitive method has been developed for the analysis of sildenafil (S) and its N-demethylated metabolite UK-103,320 (UK) using capillary gas chromatography with a flame ionisation detector. Optimal conditions were investigated, achieving analysis times shorter than 12 minutes. Aspects such as stability of the solutions, linearity, accuracy (>91%), precision, specificity, and limits of detection (0.02 mg/L and 0.12 mg/L for S and UK respectively) were tested in order to validate the method. A solid-phase extraction (SPE) prior to the analysis allows quantification of S in serum and urine, and UK in serum at clinically relevant concentrations. Furthermore the specificity has been assessed by means of mass spectrometry in SCAN mode.

Fresenius' Journal of Analytical Chemistry, 1990

Electroanalysis, 1992

... Juana Rodriguez Flores' and Jose Maria Fmandez Aluarez Departamento de Quimica Analitica... more ... Juana Rodriguez Flores' and Jose Maria Fmandez Aluarez Departamento de Quimica Analitica Urzivmsidad de Castilla ... of the cells [3]. Elevated enzyme levels can be detected in sera of patients ... voltamniogranis were recorded from a solution containing 20 ppb of .MIA under the ...

Fresenius J Anal Chem, 1998

Fresenius' Journal of Analytical Chemistry, 1997

Adsorptive stripping voltammetry was used for the determination of trace amounts of the dye Tartr... more Adsorptive stripping voltammetry was used for the determination of trace amounts of the dye Tartrazine (E-102) by square-wave (SWS) and differential pulse techniques (DPS). Its adsorptive voltammetric behaviour was investigated at different pH media. NH 4 Cl/NH 3 buffer solution was chosen as the most suitable, taking into account the sensitivity and definition of the reduction peaks obtained. The effects of the experimental parameters on the determination are discussed. Standard deviations of 3.3% and 2.6% were obtained by SWS and DPS for 100 and 50 µg/L Tartrazine solutions, respectively (n = 10). Both methods were applied to determine the dye in several commercial soft drinks, containing very small amounts of it. Measurements were made directly in the commercial samples. A comparison of the results obtained by the proposed voltammetric methods with those of an HPLC method was also made. Good correlations between the voltammetric results and the values supplied by the manufacturer were found, whereas recoveries of the same order of magnitude were obtained by the HPLC method.

Fresenius' Journal of Analytical Chemistry, 1999

A very simple spectrophotometric method is described for resolving ternary mixtures of the food d... more A very simple spectrophotometric method is described for resolving ternary mixtures of the food dyes Tartrazine (E-102), Quinoline Yellow (E-104) and Patent Blue V (E-131) by using the second derivative of the spectra with measurements at zero-crossing wavelengths. Calibration graphs are linear up to 20.0 mg/L of Tartrazine, up to 20.0 mg/L of Quinoline Yellow and up to 6.4 mg/L of Patent Blue V. Repeatability and reproducibility studies (with the Students's and F tests) were achieved for two series of nine standards for each dye showing no significant differences at the 95% confidence level. Detection limits of 0.0526, 0.0164 and 0.0034 mg/L were obtained for Tartrazine, Quinoline Yellow and Patent Blue V, respectively. This method was used for determining synthetic mixtures of these colorants in different ratios and it was successfully applied to four commercial products without previous separation step. The results found in commercial products were compared with those obtained by an HPLC method and very similar values were found for both methods.

Biosensors, 1989

The electrochemical behaviour of human chorionic gonadotropin (hCG), as well as rat anti-phCG and... more The electrochemical behaviour of human chorionic gonadotropin (hCG), as well as rat anti-phCG and rabbit anti$hCG antibodies, has been studied using cyclic voltammetry and adsorptive stripping voltammetry. Conditions have been optimised for the determination of these species by differential pulse adsorptive stripping voltammetry with respect to accumulation potential, accumulation time, scan rate, pulse amplitude and drop size. This technique has also been used to investigate the interaction of hCG with each of its specific antibodies in solution.

Analytical Proceedings, 1988

Contemporary Electroanalytical Chemistry, 1990

Since the early 1970’s there has been much interest shown in the development of non-isotopic immu... more Since the early 1970’s there has been much interest shown in the development of non-isotopic immunoassays. The main reasons for this stem from the perceived dangers of using radio-labelled substances (as required in radioimmunoassay), and the search for more selective, sensitive and precise methods of analysis. Much work has therefore been devoted to the development of fluorescent and enzyme-linked immunoassays, but it is only in recent years that there has been strong interest in the application of electrochemical techniques in this regard.1,2

Journal of Pharmaceutical and Biomedical Analysis, 1989

The adsorptive stripping voltammetric behaviour of F(ab')2 and Fab fragments of anti-mous... more The adsorptive stripping voltammetric behaviour of F(ab')2 and Fab fragments of anti-mouse immunoglobulin G is described. Conditions were optimized for the determination of these fragments with respect to accumulation potential, accumulation time, scan rate, pulse amplitude, drop size and electrolyte composition. The F(ab')2 and Fab fragments gave rise to behaviour similar to that reported previously for the intact immunoglobulin.

Journal of Chromatography B, 2004

A Micellar electrokinetic capillary chromatography method is proposed for the determination of si... more A Micellar electrokinetic capillary chromatography method is proposed for the determination of sildenafil, vardenafil and tadalafil, which are employed in oral therapy for erectile dysfunction. Optimum conditions for the separation were investigated. A background electrolyte solution consisting of 10 mM phosphate buffer adjusted to pH 12.0, sodium dodecyl sulfate (SDS) 25 mM, hydrodynamic injection, and 25 kV as separation voltage were used. Relative standard deviations (R.S.D.s) were 1.0, 1.0, 0.4% and 2.9, 2.9, 1.9% for migration time and corrected peak area (CPA) (n = 9) for sildenafil, vardenafil and tadalafil, respectively. Detection limits obtained for the three drugs ranged from 0.19 to 0.61 mg L −1. A linear concentration range between 1 and 20 mg L −1 was obtained. A ruggedness test of this method was checked using the fractional factorial model of Plackett-Burman, in which the influence of six factors at three different levels was tested on different electrophoretic results: resolution and corrected peak area. The statistical evaluation of the electrophoretic results was achieved by Youden and Steiner method. The described method is rapid, sensitive and rugged and it was tested in the pharmaceutical formulations analysis obtaining recoveries between 98 and 107% respect to the nominal content

Journal of Chromatography A, 2005

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity d... more Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of S-timolol maleate using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) as chiral selector. With a background electrolyte made up of a methanolic solution of 0.75 M formic acid, 30 mM potassium camphorsulfonate and containing 30 mM HDMS-beta-CD, the determination of 0.1% of R-timolol in S-timolol could be performed with an enantiomeric resolution of 8.5. Pyridoxine was selected as internal standard. The NACE method was then fully validated by applying a novel strategy using accuracy profiles. It is based on beta-expectation tolerance intervals for the total measurement error which includes trueness and intermediate precision. The uncertainty of measurements derived from beta-expectation tolerance intervals was estimated at each concentration level of the validation standards. To confirm the suitability of the developed and validated method, several real samples of S-timolol maleate containing R-timolol maleate at different concentrations were analysed and the results were compared to those obtained by liquid chromatography.

Journal of Chromatography A, 2002

Micellar electrokinetic capillary chromatography (MEKC) coupled with sample stacking and polarity... more Micellar electrokinetic capillary chromatography (MEKC) coupled with sample stacking and polarity switching was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320, UK) in human serum in the concentration range of clinical interest. Human serum samples spiked with SC and UK were eluted with methanol from a C18 cartridge, the extract was evaporated and regenerated in a solution that contained 1 mM phosphate buffer (pH 12.3) and 20% methanol. The MEKC separation was performed using an injection time of 275 s, a polarity switching time of 93 s, a phosphate buffer, (pH 12.3, 15 mM) containing 25 mM sodium dodecyl sulfate as separation electrolyte and a fused-silica capillary. The analysis takes about 6 min and gives satisfactory inter-day precision with respect to migration times and linear responses over the 80-900 ng/ml concentration range investigated for SC and UK. Intra-day RSDs (n=4 graphs) for the slopes of the calibration graphs were 4.86% for SC and 3.50% for UK. Inter-day RSDs for the slopes were 4.37% for SC and 5.39% for UK. Detection limits (S/N=3) were about 17 ng/ml for both compounds in human serum. A 1-ml volume of blood serum was necessary to do this determination.

Electroanalysis, 2000

The behavior of¯uvoxamine (FVX) was studied by square-wave techniques, leading to two methods for... more The behavior of¯uvoxamine (FVX) was studied by square-wave techniques, leading to two methods for its determination in aqueous samples (pH 2.0 and 4.7) and pharmaceuticals formulations. The application of the square-wave mode shows the determination of FVX between 2610 78 and 3610 76 mol L 71. FVX gave an adsorptive stripping voltammetric peak at the hanging mercury drop electrode at 7 0.76 V, using an accumulation potential of 7 0.50 V. By the stripping technique, FVX proved to be more sensitive, yielding signals ®ve times larger than those obtained by applying a square-wave scan without the previous accumulation. The calibration plot to determine FVX was linear in the range 5610 79 and 1610 76 mol L 71 by stripping mode. The relative standard deviations obtained for concentration levels of FVX as low as 1.5610 76 mol L 71 with square-wave was 3.54 % (n 10) and for 6.0610 77 mol L 71 with stripping square-wave was 2.39 % (n 10) in the same day. The two proposed methods (SW and SWAdSV) were applied to the determination of¯uvoxamine in two Spanish commercial product (Dumirox 50 and Dumirox 100) with very good recoveries respect to the labelled values.

Electroanalysis, 1989

Abstract The electrochemical behavior of whole and lysed chronic lymphocytic leukemia (CLL) cells... more Abstract The electrochemical behavior of whole and lysed chronic lymphocytic leukemia (CLL) cells, as well as that of two murine anti-CLL antibodies, has been studied using differential pulse adsorptive voltammetry. Conditions have been optimized for the ...

Electroanalysis, 1999

Abstract The behavior of gestodene (GTD) was studied by square-wave techniques, leading to two me... more Abstract The behavior of gestodene (GTD) was studied by square-wave techniques, leading to two methods for its determination in aqueous samples and pharmaceutical formulations. The application of the square-wave mode shows the determination of GTD between 2× 10 ...