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A Molina-Díaz

Publications and source records attributed to A Molina-Díaz.

11 recordsLinked to original sources
PubMed2006

Development of a multicommuted flow-through optosensor for the determination of a ternary pharmaceutical mixture.

The combination of multicommutation and flow-through multioptosensing is presented in this work as a powerful strategy for the routine analysis of active principles in pharmaceuticals. By coupling methodologies, the selectivity and sensitivity of optosensors is maintained, while the use of the multicommutation approach provides additional advantages, such as low reagent consumption, low waste generation and reduced human supervision. The potential of this integration is enhanced when implemented with multiwavelength detection mode. An UV sensor is here developed for the simultaneous determination of three widely used active principles: salicylamide, caffeine and propyphenazone. The measuring wavelengths were 276 nm for caffeine and propyphenazone, and 302 nm for salicylamide. The five three-way solenoid valves used in the system are controlled by Java-written home-made software. The sensor is based on the on-line selective retention of two of the three analytes on a precolumn placed just before the sensing zone and filled with the same solid support than the flow-through cell (C(18) silica gel). This approach allows the sequential arrival of the analytes to the sensing zone, so allowing their determination with only one sample injection. So, the use of C(18) placed, in both the precolumn and the flow-cell combines the advantages of the increase of sensitivity and selectivity in the detection solid zone with the additional increase of the selectivity in the precolumn. The sensor was applied to the determination of the analytes in several pharmaceutical preparation of the Spanish Pharmacopoeia, obtaining satisfactory results.

Antipyrine↗
PubMed2005

Multicommuted flow-through fluorescence optosensor for determination of furosemide and triamterene.

Multicommutation implemented with flow-through optosensors is a very promising area of research. This recent approach benefits from the advantages of both methods and results in high sensitivity, selectivity, and speed, and little waste generation. This paper reports the simultaneous determination of furosemide and triamterene, two widely used diuretics, by measurement of their native fluorescence. The system has been proved to be useful for determination of both analytes in pharmaceutical preparations and for determination of triamterene in human urine and serum. A minicolumn filled with Sephadex SPC-25 microbeads was used to achieve separation of both analytes before detection in a flow-through cell filled with the same resin. The sensor is linear in the range 50-1200 and 0.4-8 ng mL(-1) with detection limits of 15 and 0.1 ng mL(-1) for furosemide and triamterene, respectively.

Blood Chemical Analysis↗
PubMed2005

Solid-phase ultraviolet sensing system for determination of methylxanthines.

In this study the use of a single continuous-flow solid-phase UV spectrophotometric sensing system for determination of methylxanthines was evaluated. Two methods were developed to determine caffeine (CF) and theophylline (TP) in pharmaceuticals and CF and theobromine (TB) in food and beverages. The sensor is based on transient and sequential retention of the analytes on a hydrophobic sensing solid zone (octadecyl silane C18 gel) and detection of their intrinsic UV absorbance. Temporary sequencing of the arrival of the analytes at the sensing zone is achieved by on-line separation of one of the analytes using a pre-column of the same particulate material, placed just before the flow cell. After TB or TP had been carried toward the sensing zone (by the appropriate carrier solution), produced its transitory signal, and been eluted by the carrier, an appropriate eluting solution (25% MeOH) was used to elute CF, which was strongly retained on the minicolumn, so that its transient signal could be recorded. The sensing zone was completely regenerated with this eluting solution, and so was ready for analysis of another sample. After selecting the most suitable conditions, the sensing system was calibrated in the range 1-16 and 1-12 mg L(-1) for CF and TP-TB, respectively, giving detection limits below 0.1 mg L(-1) with RSD values less than 3%. The usefulness of this approach has been evaluated by applying it to the determination of caffeine, theobromine, and theophylline in different samples of food, beverages, and pharmaceutical formulations. The results were in satisfactory agreement with those obtained by use of an HPLC reference method.

Chromatography, High Pressure Liquid↗
PubMed2005

Resolution of biparametric mixtures using bead injection spectroscopic flow-through renewable surface sensors.

A new, sensitive and simple bead injection spectroscopy-flow injection analysis (BIS-FIA) sensor with spectrophotometric detection, using a commercially available flow-cell, is described to the determination of biparametric mixtures. As an analytical model, the metallic mixture Cu(II) and Zn(II) has been chosen. The flow-cell (Hellma 138-OS) is filled by injecting in the flow system 300 microl of a homogeneous bead suspension of an anion exchanger gel (Sephadex QAE A-25) previously loaded with the chromogenic reagent 2-carboxyl-2-hydroxy-5-sulfoformazylbenzene (Zincon). A sequential reaction of Cu(II) and Zn(II) with Zincon to form two complexes is performed on the bead sensing support and the absorbance is monitored at 627 nm, after two successive injections from the mixture solution. The sample containing these metal ions is injected into the first carrier (deionized water, pH 5.9), and Cu(II) selectively reacts with Zincon on the beads, developing the analytical signal. Then, 600 microl of 2 M HCl is injected to decompose the complex, and the carrier solution is changed. At pH 11 (second carrier) both Cu(II) and Zn(II) react with the chromogenic reagent, the absorbance now corresponding to both analytes. The eluent is again injected to descompose both complexes. After three analyses the sensing bead surface is not regenerated. Then, beads are automatically discarded from the flow cell by reversal of the flow, and instantaneously transported out of the system. So the procedure exploits the combination of the concepts of flow-through renewable sensors with bead injection spectroscopy. Using a sample volume of 1000 microl, the calibration graph for Cu(II) is linear over the range 0.05 to 1 microg ml(-1) and for Zn(II) from 0.1 to 1.8 microg ml(-1) in the presence of each other. RSDs (%) lower than 5% are obtained for both analytes. The sensor is satisfactorily applied to individual determination or mixture resolution in waters, pharmaceuticals, soils and human hair samples.

Azo Compounds↗
PubMed2002

A flow-through solid-phase spectroscopic sensing device implemented with FIA solution measurements in the same flow cell: determination of binary mixtures of thiamine with ascorbic acid or acetylsalicylic acid.

A continuous and simple UV-photometric flow-through optosensor has been developed for the simultaneous determination of a binary mixture of two species with different electric charges present at very different concentrations - ascorbic acid (or acetylsalicylic acid) and thiamine. The sensing device is based on the selective sorption and determination of a cationic analyte on a cation-exchange gel (Sephadex SP-C25) while the other, anionic, analyte is determined in the solution among the interstices of the cation-exchange gel in the same flow cell. The analytes arrive in sequence at the sensing zone, which detects their intrinsic absorbance at 253 nm, as a result of on-line separation by use of a minicolumn filled with the same cation-exchange gel as in the cell, and placed before the flow cell. Thiamine is retained in the minicolumn whereas ascorbic acid or acetylsalicylic acid pass through it and produce their signal as a result of absorbance in the interstitial solution among the resin beads. Thiamine is then eluted from the precolumn, transported to the flow cell, and temporarily retained in the sensing zone from this eluted solution. Calibration graphs were linear over the range 3-50, 25-400, and 300-3000 microg mL(-1) (600 microL sample volume) and the relative standard deviations were 2.56, 1.85, and 1.25 % for thiamine, ascorbic acid, and acetylsalicylic acid, respectively. The proposed method was satisfactorily applied to the determination of binary mixtures of thiamine with ascorbic acid or acetylsalicylic acid in pharmaceutical preparations and semi-synthetic samples.

Ascorbic Acid↗
PubMed2002

Determination of triamterene by transitory retention in a continuous flow solid phase system with fluorimetric transduction.

A rapid and simple flow-through solid phase espectrofluorimetric system (sensor) is described in this paper for the determination of the diuretic triamterene at ng ml(-1) level in physiological fluids and in pharmaceuticals. This sensor is based on the transitory retention of the analyte on the cationic ion-exchanger gel Sephadex SP C-25 placed into a quartz flow-cell in the detection zone itself of a spectrofluorimeter and the continuous monitorization of its intrinsic fluorescence. The spectrofluorimeter was tuned at 240 (excitation) and 440 nm (emission). A transitory signal was obtained because the carrier solution used also eluted the analyte from the sensing zone and no derivatization reactions were needed. Triamterene could be determined in the concentration ranges of 10-400 and 2.5-80 ng ml(-1) with detection limits of 0.95 and 0.17 ng ml(-1) for 300 and 1000 microl of sample volume, respectively. The relative standard deviations (RSD) for ten independent determinations and at three concentration levels of standards solutions were lower than 0.90 for 300 microl and 0.45 for 1000 microl. The RSDs for the determination of triamterene in serum samples and pharmaceuticals were lower than 3.3 and 2.6%, respectively. The method was satisfactorily applied to the determination of triamterene in human serum and pharmaceuticals.

Calibration↗
PubMed2002

Simultaneous determination of paracetamol and caffeine by flow injection-solid phase spectrometry using C18 silica gel as a sensing support.

A continuous and simple UV-photometric flow-through biparameter-sensing device has been developed for the simultaneous determination of paracetamol and caffeine at 275 nm. The sensor is based on temporary sequentiation in the arrival of the analytes to the sensing zone by on-line separation using C18 bonded phase beads (the same as that used in the sensing zone) placed into a minicolumn just before the flow cell. The sample containing these compounds is injected into the carrier solution; paracetamol is determined first because it passes through the minicolumn, while caffeine is strongly retained in it. Then, caffeine is conveniently eluted from the precolumn and develops its transitory signal. Using 200 microl of a sample and deionized water as a carrier, the analytical signal showed a very good linearity in the ranges of 10-160 microg ml(-1) and 3.5-50 microg ml(-1) with detection limits of 0.75 and 0.56 microg ml(-1) for paracetamol and caffeine, respectively. If deionized water with the pH adjusted at 12 was used as a carrier solution, these parameters were 25-400 and 4-55 microg ml(-1) with 2.0 and 0.50 microg ml(-1) as the detection limits, respectively. The biparameter optosensor was satisfactorily applied to the simultaneous determination of these two analytes in pharmaceuticals.

Acetaminophen↗
PubMed2001

Flow-through UV spectrophotometric sensor for determination of (acetyl)salicylic acid in pharmaceutical preparations.

The solid phase spectrophotometry technique, in which the absorbance of the species of interest sorbed on a solid support is measured directly, was applied to the determination of salicylic acid using flow injection-analysis. Salicylic acid was determined by monitoring of its intrinsic absorbance at 297 nm sorbed on Sephadex QAE A-25 resin placed in an appropriate flow-through cell. The method proposed improves the selectivity compared with the corresponding solution-phase method and the sensitivity is increased by a factor of 30 or more. The flow-through sensor proposed allows working with several calibration lines simply by varying the sample volume injected. Thus, linear dynamic ranges from 1 to 20 and from 2 to 40 microg ml(-1) can be obtained by using 1000 and 300 microl, respectively, with detection limits being 0.064 and 0.135 microg ml(-1). Relative Standard Deviations (RSDs) of 0.52 and 0.38%, and sampling frequencies of 18 and 25 h(-1), respectively, were also achieved. The sensor also allows the indirect determination of acetylsalicylic acid previous hydrolysis on-line to salicylic acid. For acetylsalicylic acid, a linear dynamic range from 5 to 120 microg ml(-1) and 25 h(-1) of sampling frequency (300 microl of sample volume) were obtained. The proposed flow-through sensor has been successfully applied to the determination of both analytes in pharmaceutical preparations.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

A flow-through optosensing device with fluorimetric transduction for rapid and sensitive determination of dipyridamole in pharmaceuticals and human plasma.

A flow-through optosensor with fluorimetric transduction has been prepared for the sensitive and selective determination of dipyridamole in aqueous solutions and biological fluids. The method is based on a monochannel flow-injection analysis system using Sephadex QAE A-25 resin, placed into a Hellma 176-QS fluorimetric flow-through cell, as an active sorbing substrate. The native fluorescence of dipyridamole fixed on the solid sorbent is continuously monitored at wavelengths of 305 and 490 nm for excitation and emission, respectively. After obtaining the maximum fluorescence intensity, the eluent solution (KH(2)PO(4)/NaOH buffer solution, c(T)=0.05 mol l(-1), pH 6.0) is allowed to reach the flow cell, the analyte is removed, and the resin support is regenerated. When an NaOH (10(-4) mol l(-1))/NaCl (0.1 mol l(-1)) solution is used as carrier solution, at a flow-rate of 1.56 ml min(-1), the sensor responds linearly in the measuring range of 10-500 microg l(-1) with a detection limit of 0.94 microg l(-1) and a throughput of 22 samples per hour (300 microl of sample volume). The relative standard deviation for ten independent determinations (200 microg l(-1)) is less than 0.82%. The method was satisfactorily applied to the determination of dipyridamole in pharmaceutical preparations and human plasma.

Chemistry, Pharmaceutical↗
PubMedDate not supplied

Application of liquid chromatography to the simultaneous determination of acetylsalicylic acid, caffeine, codeine, paracetamol, pyridoxine, and thiamine in pharmaceutical preparations.

This paper describes a rapid reversed-phase liquid chromatographic method, with UV detection, for the simultaneous determination of acetylsalicylic acid, caffeine, codeine, paracetamol, pyridoxine, and thiamine in pharmaceutical preparations. A reversed-phase C18 Nucleosil column is used. The mobile phase consists of 2 successive eluants: water (5 min) and acetonitrile-water (75 + 25, v/v; 9 min), both adjusted to pH 2.1 with phosphoric acid. Before determination acetylsalicylic acid is completely converted to salicylic acid by alkaline hydrolysis. Salicylic acid, caffeine, paracetamol, pyridoxine, and thiamine are all detected at 285 nm, whereas codeine is detected at 240 nm. Calibration curves were linear for salicylic acid, caffeine, paracetamol, and pyridoxine in the range of 50-500 mg/L, and for codeine and thiamine in the range of 50-1000 mg/L. The method was applied to the analysis of 13 fortified commercial pharmaceutical preparations. Recoveries ranged from 92.6 to 105.5%, with relative standard deviations of 1.1-5.8%.

Acetaminophen↗