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A Molina Díaz

Publications and source records attributed to A Molina Díaz.

11 recordsLinked to original sources
PubMed2005

Effect of polyethyleneimine ion on the sorption of a reactive dye onto Leacril fabric: electrokinetic properties and surface free energy of the system.

Data are presented on the kinetics, electrokinetics, and surface free energy in the process of adsorption of polyethyleneimine (PEI) as a pretreatment of Leacril, later dyed with the reactive dye Remazol Brilliant Blue R (RBBR). The electrokinetic potential of Leacril is negative, due probably to the presence of sulfonate and sulfate end-group onto Leacril fibers. The zeta potential of Leacril decreases in absolute value as a function of NaCl concentration in solution, probably because of compression of the electrical double layer. The zeta potential of Leacril as a function of the concentration of PEI in solution increases because of the adsorption of PEI ions through chemical reaction between the sulfonate end-groups of Leacril and the amine groups of PEI. The adsorption kinetics shows that an increase in the concentration of PEI, brings about an increase in the amount of RBBR adsorbed onto the fiber. This may be an indication of the chemical reaction between the reactive groups of the polyelectrolyte and dye molecules. The behavior of the surface free energy of the systems involved confirms these conclusions.

Journal Article↗
PubMed2004

Bead injection spectroscopy-flow injection analysis (BIS-FIA): an interesting tool applicable to pharmaceutical analysis. Determination of promethazine and trifluoperazine.

A bead injection spectroscopy-flow injection analysis (BIS-FIA) system for the spectrophotometric detection of promethazine and trifluoperazine is developed. The sensor is based in the oxidation of the phenothiazines by Fe(III) which is later determined by formation of the complex between Fe(II) and Ferrozine, [FeFz(3)](4-). Immediately, this complex is retained on a homogeneous bead suspension of Sephadex QAE A-25 resin (500 microl) which has been injected previously in the system to fill a commercial flow-cell (Hellma 138-OS). The use of BI with respect to the use of a reusable flow-through sensor is justified because the complex is so strongly retained on the beads that the regeneration of the solid support becomes extraordinarily difficult in the proposed method. At the end of the analysis, beads are automatically discarded from the flow-cell, by reversing the flow, and transported out of the system. The analytical signals are measured at a wavelength of 567 nm, corresponding to the absorbance of the complex. Using a sample volume of 600 microl, the analytical signal showed a very good linearity in the range 0.5-8.0 microgml(-1) and 0.5-10.0 microgml(-1), with detection limits of 0.09 and 0.14 microgml(-1) for promethazine and trifluoperazine, respectively. R.S.D.s (%) lower than 2% were obtained for both analytes. The proposed method is highly selective in the presence of other species that are normally encountered with these analytes. The sensor was satisfactorily applied to pharmaceutical preparations.

Dosage Forms↗
PubMed2003

Continuous-flow separation and pre-concentration coupled on-line to solid-surface fluorescence spectroscopy for the simultaneous determination of o-phenylphenol and thiabendazole.

A novel and single flow-injection system combined with solid-surface fluorescence detection is proposed in this work for the resolution of a mixture of two widely used pesticides (o-phenylphenol and thiabendazole). The continuous-flow methodology is based on the implementation of on-line pre-concentration and separation of both analytes on the surface of C18 silica gel beads placed just inside the flow cell, implemented with gel-phase fluorimetric multi-wavelength detection (using 305/358 and 250/345 nm as excitation/emission wavelengths for thiabendazole and o-phenylphenol, respectively). The separation of the pesticides was possible owing to the different retention/desorption kinetics of their interactions with the solid support in the zone where the stream impinges on the solid material. No previous separation of the analytes before they reach the flow cell is needed thereby simplifying substantially both the procedure and the manifold. By using a sample volume of 2,600 microL, the system was calibrated in the range 0.5-16 and 5-120 ng mL(-1) with detection limits of 0.09 and 0.60 ng mL(-1) for thiabendazole and o-phenylphenol, respectively. The RSD values (n=10) were about 1% for both analytes. The proposed methodology was applied to environmental water samples and also to various commercial pesticide formulations containing both analytes. Recovery percentages were 97-103% and 98-102% for thiabendazole and o-phenylphenol, respectively.

Journal Article↗
PubMed2003

New contributions to the field of bead-injection spectroscopy-flow-injection analysis: determination of cobalt.

A bead-injection spectroscopy-flow-injection analysis (BIS-FIA) system with spectrophotometric detection has been developed for the determination of cobalt. A homogeneous bead suspension of Dowex 50 W resin (600 microL) previously loaded with the chromogenic reagent 1-(2-pyridylazo)-2-naphthol (PAN) was injected to fill the flow-cell. Co is injected into the carrier (pyrophosphate, pH 5) and reacts with the immobilized chromogenic reagent to form a green chelate. The analytical signal corresponds to the formation of the Co-PAN complex on the solid surface. At the end of the analysis, the beads are discarded by reversing the flow and instantaneously transported out of the system. The sensor shows both excellent selectivity, which could also be increased with a simple on-line modification to avoid interferences from Ni(II), Zn(II) and Cu(II), and good sensitivity; the detection limit was 19 ng mL(-1), the linear range 50-2000 ng mL(-1) and the RSD (%) 4.16. The method was satisfactorily applied to the determination of Co in waters, pharmaceuticals and alloy steels.

Calibration↗
PubMed2003

A flow injection sensor for simultaneous determination of sulfamethoxazole and trimethoprim by using Sephadex SP C-25 for continuous on-line separation and solid phase UV transduction.

A flow-through sensor based on integration of spectrophotometric detection and the different kinetics of retention/elution of analytes on a solid support is proposed for the simultaneous determination of sulfamethoxazole (SMZ) and trimethoprim (TMP). The solid support (Sephadex SP C-25) fills both, a microcolumn placed on-line and the sensing microzone. The intrinsic absorbance of both compounds is monitored directly on the solid phase at 269 nm and so, no derivatization step is required. Using two alternate solutions, 10(-4) M hydrochloric acid and 0.20 M NaAc/HAc (pH 5.0) buffer, the sensor responds linearly in the measuring range of 50-250 and 10-70 microg ml(-1) with detection limits of 9.5 and 0.6 microg ml(-1) (500 microl of sample volume) for SMZ and TMP, respectively. The main advantages of the sensor are simplicity, rapidity and low reagents consumption. Its application to SMZ and TMP determination in synthetic samples and pharmaceutical preparations is demonstrated. The results obtained by the proposed method were compared with those obtained by a standard HPLC method.

Chromatography, High Pressure Liquid↗
PubMed2003

Fast and single solid phase fluorescence spectroscopic batch procedure for (acetyl) salicylic acid determination in drug formulations.

A solid phase fluorescence spectroscopic batch procedure for (acetyl) salicylic acid in drug formulations have been developed. The procedure is based on the sorption of salicylic acid (SA) on Sephadex DEAE A-25 anion exchanger gel (100 mg) by equilibration from an aqueous solution (10 or 25 ml) for 5 min; the equilibrated gel is transferred into an 1 mm quartz cell and the native fluorescence of SA sorbed on it is directly measured (lambda(ex)=297 nm; lambda(em)=405 nm). Good linearity was found in the 10-200 and 5-100 microg l(-1) ranges (for 10 and 25 ml sample volume, respectively) with R.S.D. (%) of 2.8 and 1.1. The procedure was successfully applied to the determination of acetyl salicylic acid (ASA) in drug formulations after alkaline hydrolysis to yield SA.

Algorithms↗
PubMed2002

The potential of flow-through optosensors in pharmaceutical analysis.

The fundamental principles of flow-through optosensors, together with the most significant procedures and alternatives developed in the applications of flow-through optosensors to pharmaceutical analysis are reviewed. The most frequently used solid sensing zones, flow-through cells, manifolds, regeneration step and types of detection are considered. Single parameter, biparameter, and multiparameter sensors developed are reviewed and their most relevant features presented. Finally, a critical comparison with other analytical methodologies/techniques is performed and the potential of flow-through optosensors in pharmaceutical analysis and their future trends discussed.

Chemistry, Pharmaceutical↗
PubMed2001

Simultaneous determination of thiamine and pyridoxine in pharmaceuticals by using a single flow-through biparameter sensor.

For the first time, an UV-photometric flow-through sensing device has been developed for the simultaneous determination of two cationic species (thiamine and pyridoxine). The sensor is based on the retention of the analytes on a cationic ion-exchanger gel placed in the detection zone itself into a quartz flow-cell. A double discrimination is used for detecting the analytes: (a) a double and simultaneous working wavelength, performed by the use of a diode array detector; and (b) a temporary sequentiation in the arrival of the analytes to the sensing zone by on line separation using a cationic ion-exchanger (the same used in the sensing zone) placed into a minicolumn just before the flow cell. Pyridoxine is determined the first (by measuring its intrinsic absorbance at 293 nm) because it passes through the minicolumn while thiamine is strongly retained on it. Then, thiamine is conveniently eluted from the precolumn and its intrinsic UV absorbance measured at 255 nm. In both cases, transitory signals were obtained because both the carrier (in the case of the pyridoxine) and the eluting (in the case of thiamine) solutions used also eluted the respective analyte from the sensing zone. Using 1000 microl of sample, the analytical signal showed a very good linearity in the range 2-30 microg ml(-1) for both analytes with detection limits of 0.10 and 0.084 microg ml(-1) for thiamine and pyridoxine, respectively. The optosensor was satisfactorily applied to the determination of these two analytes in pharmaceuticals.

Flow Injection Analysis↗
PubMed2000

Selective determination of pyridoxine in the presence of hydrosoluble vitamins using a continuous-flow solid phase sensing device with UV detection.

A very simple, inexpensive and highly selective flow injection UV spectrophotometric method for the determination of vitamin B(6) is presented. The native absorbance of the analyte is continuously monitored at 290 nm when it is transiently retained on Sephadex SP C-25 cation exchanger gel beads placed in the detection area of a flow cell. The preconcentration on the active solid phase provides by itself a high increase in sensitivity compared with the same procedure carried out without a solid support. The analytical response is linear in the concentration ranges 1-10 and 2-20 microg ml(-1) using 600 and 1250 microl of sample, respectively. The R.S.D. (%) are 0.65 (600 microl) and 0.84 (1250 microl) and the detection limits 0.08 and 0.02 microg ml(-1), respectively. The procedure was successfully applied to the determination of vitamin B(6) in pharmaceuticals containing (among other active principles) hydrosoluble vitamins in much higher concentrations than that tolerated by the method if performed in aqueous solution. Nevertheless they were tolerated using the proposed sensor due to the selective retention of the analyte.

Ascorbic Acid↗
PubMed2000

Fast determination of paracetamol by using a very simple photometric flow-through sensing device.

A simple flow-through UV optosensing device was developed for the determination of paracetamol based on its transient retention and concentration on a suitable active solid support (Sephadex QAE A-25 anion-exchange resin) packed in the flow cell and the continuous monitoring of its native absorbance on the solid phase at 264 nm. The sample was injected into a 0.08-M NaCl carrier stream at pH 11.0 by using a simple monochannel FIA manifold. After developing the analytical signal, paracetamol was desorbed from the solid support by the carrier solution itself. A very good linear response was found in the concentration range 0.5-8.0 microg ml(-1) with a RSD (%) of 1.24, a detection limit of 0.022 microg ml(-1) and a sampling rate of 40 h(-1). A strong increase in sensitivity as well as a very much higher selectivity were achieved as compared with the conventional flow injection method as a consequence of the separation of the analyte from the sample plug and its retention on the active solid support placed in the detection area. Applicability of the proposed sensor to direct determination of paracetamol in pharmaceuticals (to solve the sample being the only treatment) was successfully demonstrated.

Acetaminophen↗