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Biomedical subjects

L F Capitán-Vallvey

Publications and source records attributed to L F Capitán-Vallvey.

At least 19 recordsLinked to original sources
PubMed2006

A simplified measurement procedure and portable electronic photometer for disposable sensors based on ionophore-chromoionophore chemistry for potassium determination.

A field-portable photometer for potassium determination with disposable sensors has been developed. It can be applied to routine water and beverage analysis. The disposable sensor is based on ionophore-chromoionophore chemistry. A colour change in the sensing film is detected by measuring the transmitted intensity with a solid state photodetector. Optical excitation at 660 nm is emitted by a light-emitting diode (LED). Negative feedback for LED bias and thermal correction were included to improve system stability. Additionally, a measurement procedure is presented, characterized and validated for in situ photometer use and real-time results. This simplified procedure is based on prior preparation of the disposable sensor in its acidic form and on the use of an absorbance ratio as analytical parameter. The only requirement for analysis is prior equilibration with a buffered sample solution for 3 min and absorbance measurement before and after equilibration. Good sensitivity in the concentration range 5 muM to 100 mM and very good repetitively and stability were achieved that are comparable to those obtained with bulkier analytical instrumentation. Given the compact size, low weight, rapid response and low energy requirement of the electronic photometer developed here, this measurement system is suitable for potassium determination in the field.

Chemical Phenomena↗
PubMed2006

Resolution of an intense sweetener mixture by use of a flow injection sensor with on-line solid-phase extraction. Application to saccharin and aspartame in sweets and drinks.

An integrated solid-phase spectrophotometry-FIA method is proposed for simultaneous determination of the mixture of saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide; E-954) (SA) and aspartame (N-L-alpha-aspartyl-L-phenylalanine-1-methyl ester; E-951) (AS). The procedure is based on on-line preconcentration of AS on a C18 silica gel minicolumn and separation from SA, followed by measurement, at lambda = 210 nm, of the absorbance of SA which is transiently retained on the adsorbent Sephadex G-25 placed in the flow-through cell of a monochannel FIA setup using pH 3.0 orthophosphoric acid-dihydrogen phosphate buffer, 3.75x10(-3) mol L(-1), as carrier. Subsequent desorption of AS with methanol enables its determination at lambda = 205 nm. With a sampling frequency of 10 h(-1), the applicable concentration range, the detection limit, and the relative standard deviation were from 1.0 to 200.0 microg mL(-1), 0.30 microg mL(-1), and 1.0% (80 microg mL(-1), n = 10), respectively, for SA and from 10.0 to 200.0 microg mL(-1), 1.4 microg mL(-1), and 1.6% (100 microg mL(-1), n = 10) for AS. The method was used to determine the amounts of aspartame and saccharin in sweets and drinks. Recovery was always between 99 and 101%. The method enabled satisfactory determination of blends of SA and AS in low-calorie and dietary products and the results were compared with those from an HPLC reference method.

Aspartame↗
PubMed2004

A test strip for chloride analysis in environmental water.

A disposable and reversible test strip for chloride is proposed. It is based on a polyester strip containing a circular sensing zone, 6 mm in diameter and 9.5 microm in thickness, with all the reagents necessary to produce a selective response to chloride. This sensing zone comprises a plasticized poly(vinyl chloride) (PVC) membrane that incorporates trioctyltin chloride as ionophore and 4',5'-dibromofluorescein octadecyl ester as chromoionophore. The prepared test strip works on a co-extraction system of chloride and hydrogen ions in the sensing zone. This disposable test strip can determine chloride simply by introducing the strip into a water sample containing a pH 2.0 buffer and measuring the absorbance at 534 nm as the analytical signal because the colour changes from red to orange. Experimental variables that influence the sensor response have been studied, especially those related to selectivity and response time. The sensor responds linearly in activities in the range 0.15-24.7 mM. The detection limit is 0.15 mM, the intermembrane reproducibility at a mid-level of the range is 6.4% relative standard deviation (RSD) of log aCl- and the intramembrane reproducibility is 4.5%. The procedure was applied to the determination of chloride in different types of water (tap, well, stream and sea), validating results against a reference procedure. This proposed test system for chloride determination in waters is inexpensive, selective and sensitive and uses only conventional instrumentation.

Journal Article↗
PubMed2004

Calcium selective test strip for water and milk.

We have developed a selective and reversible test strip based on an ion-exchange mechanism to determine calcium. The optical test strip contains a polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to calcium, among them the new ionophore, 4,13-bis[(N-adamantylcarbamoyl)propionyl]-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane. The measurement of the absorbance at 655 nm in a standard photometer makes it possible to determine calcium activities. The composition of the membrane and reaction conditions have been adjusted to obtain adequate selectivity. The test strip responded linearly to calcium between 0.050 and 135 mM in activities. The reproducibility intermembrane at a medium level of the range was 6.2%, as RSD, of log a(Mg(2+)), and 3.4% as RSD intramembrane. The procedure was applied to the determination of calcium ion in different types of waters (tap, well, spring and mineral) and milks (whole, skimmed, skimmed with calcium added, special types) validating the results against a reference procedure.

Animals↗
PubMed2004

Flow-through spectrophotometric sensor for the determination of saccharin in low-calorie products.

A simple, rapid and inexpensive monoparameter flow-through sensor has been developed for the determination of saccharin in low calorie and dietary products. The method is based on the transient adsorption of the sweetener on Sephadex G-25 solid phase packed to a height of 20 mm in the flow cell. The optimal transient retention of the synthetic sweetener, in terms of sensitivity and sampling frequency, was obtained when pH 2.75 citric acid-sodium citrate buffer 5 x 10(-3) M was used as a carrier at a flow-rate of 1.5 ml min(-1). Saccharin was determined measuring its intrinsic absorbance at 217 nm at its residence time. Calibration graphs for peak height and peak area were linear over the range 5.0-200.0 microg ml(-1), RSD 1.18%, and 1.0-200.0 microg ml(-1), RSD 0.78%, respectively. Saccharin was determined in several food samples measuring height or area peak, obtaining recoveries ranging between 98-104 and 99-102% for height and area peak, respectively. The procedure was validated for use in the determination of saccharin in low calorie and dietary products giving reproducible and accurate results.

Beverages↗
PubMed2004

Flow-through spectrophotometric sensor for the determination of aspartame in low-calorie and dietary products.

A very simple flow-through sensor is presented for the determination of the intense sweetener aspartame in low-calorie and dietary products. The sensor is implemented in a monochannel flow-injection system with UV spectrophotometric detection using a Sephadex CM-C25 cationic exchanger packed 20 mm high in a flow cell. This method is based on the transient retention of a cationic species of the sweetener on the solid phase when a pH 5.0 acetic acid sodium acetate buffer (0.01 M) is used as a carrier (2.6 mL(-1) min). The carrier itself elutes the analyte from the solid support, regenerating a sensing zone. Aspartame was determined by measuring its intrinsic absorbance at 219 nm at its residence time without any derivatization. Calibration graphs were linear over the range of 5.0 - 600.0 microg mL(-1) with an RSD of 0.55% (peak height). This sweetener was determined in several samples by measuring the height or peak area, obtaining recoveries ranging between 95 - 101% and 97.5 - 101%, respectively. The procedure was validated for its use in the determination of aspartame in low-calorie and dietary products, giving reproducible and accurate results.

Aspartame↗
PubMed2003

Solid-phase spectrophosphorimetric determination of the pesticide o-phenylphenol in water and vegetables.

A phosphorimetric method for the determination of o-phenylphenol (OPP) using filter paper as solid support and Tl(I) as heavy metal enhancer of the phosphorescent signal is proposed. The phosphorescence measurements were carried out by placing the paper with the sample between two plates of quartz, thus avoiding the quenching effect produced by atmospheric oxygen and moisture. The linear dynamic range of the method was 0.5-4.0 mg L(-1) and the detection and quantification limits were 0.03 and 0.11 mg L(-1), respectively. The precision of the method (expressed as relative standard deviation) was 1.7% for a sample containing 2.0 mg L(-1) of analyte. The method has been applied to the determination of OPP in different types of water, lettuce, string beans and peppers, with recoveries ranging between 97.1 and 100.7%

Biphenyl Compounds↗
PubMed2002

Test strip for determination of nitrite in water.

A disposable test strip is proposed for the determination of nitrite in waters. The strip is an inert rectangular strip of polyester with a 6 mm o.d. circular, transparent and colorless film attached to its surface. This film contains the chemicals required for reaction and fixation of the dye formed, sulfanilamide, N-(1-naphthyl)ethylenediamine on Nafion. When the test strip is placed in an acidified (pH 2.0) sample solution containing nitrite a red-violet color develops; the absorbance of this is measured at 536 nm. The linear range of the method depends on the time of equilibration of the test strip with the sample solution. When the equilibration time was 45 min, the linear range was 8.9-500 microg L(-1) whereas for an equilibration time of 60 min it was 4.7-200 microg L(-1). The detection limit was 1.4 microg L(-1) for an equilibration time of 60 min. The precision of the method, expressed as RSD, was 8.8 % at 100.0 microg L(-1). The method was applied, and validated chemometrically, for the determination of nitrite in different types of water (spring, mineral, tap, well, and sea).

Color↗
PubMed2001

Single-use optical sensor for the determination of iron in water and white wines.

A new method, based on the use of a disposable sensor, for the determination of Fe(II) in waters and wines is proposed. The sensor is formed by an inert rectangular strip of polyester (Mylar) and a circular film (6 mm in diameter) adhered on its surface. This film, which contains the required reagents for the fixation of the analyte by means of a complexation reaction, forms the sensing zone of the sensor. When the sensor is introduced in an acidified (pH 2.5) sample solution containing between 4.0 and 300.0 micrograms/L of Fe(II), a violet-red colour develops in the initially colourless sensing zone. The linear range of the method depends on the equilibration time of the sensor with the sample solution. Thus, when the equilibration time was 5 min, the linear range was 41.0-300.0 micrograms/L, while for 60 min the range was 4.0-50.0 micrograms/L. Detection and quantification limits were 12.0 and 41.0 micrograms/L, respectively, for an equilibration time of 5 min. The precision of the method, expressed as relative standard deviation of ten samples of 100.0 micrograms/L of Fe(II), was 4.9%. Interferences produced by other species usually present in waters or wines have been studied. Cu(II) and Co(II) interfered seriously at concentration levels higher than 100.0 and 150.0 micrograms/L, respectively. The method was applied to the determination of Fe(II) in different types of waters and wines, using atomic absorption spectrometry as a reference method.

Colorimetry↗
PubMed2001

Monoparameter sensors for the determination of the antioxidants butylated hydroxyanisole and n-propyl gallate in foods and cosmetics by flow injection spectrophotometry.

A flow-through optosensor with solid phase UV spectroscopic detection is proposed for the direct determination of single antioxidants, namely butylated hydroxyanisole (BHA) and n-propyl gallate (n-PG), without previous derivatization. The methods are based on the transient retention behaviour of these compounds in a flow-through cell packed with C-18 silica using ethanol-water mixtures as a carrier, and on the intrinsic absorbance monitored at 290 and 283 nm, respectively. After recording the analytical signal, the antioxidants were easily and quickly desorbed from the solid support by the same carrier. For BHA, calibration graphs were linear over the range 1.0-300.0 mg L-1 using area as the analytical parameter. The relative standard deviation (RSD) was between 0.5 and 1.6%. For n-PG, calibration graphs were linear over the range 1.0-300.0 mg L-1 in area and the RSD was between 1.4 and 1.5%. The methods were applied to the determination of these antioxidants in several food and cosmetics samples, and were validated using the standard additions method and an HPLC reference method.

Antioxidants↗
PubMed2000

Flow injection analysis with in-line solid phase extraction for the spectrophotometric determination of sulfonated and unsulfonated Quinoline Yellow in Cologne.

An integrated solid-phase spectrophotometry/ FIA method is proposed for the determination of the synthetic colorant matter Quinoline Yellow (QYWS) in the presence of its unsulfonated derivative QYSS. The procedure is based on the retention and preconcentration of the low level QYSS on a C-18 silica gel minicolumn, followed by sequential measurement of its absorbance at lambda = 410 nm after its elution with methanol. The applicable concentration range, the detection limit and the relative standard deviation were the following: for QYWS, from 0.10 to 30.0 mg L(-1); 0.013 mg L(-1); and 0.6%; and for QYSS, between 10 and 1.000 microg L(-1); 2 microg L(-1); and 1.3%, respectively. The method was applied to the determination of small amounts of QYSS present in QYWS in Colognes. Percentages of recovery between 98% and 99% were obtained in all instances. The method was also satisfactorily applied to the determination of these compounds in samples of commercial Colognes comparing the results for QYWS with those offered by an HPLC reference method and also validating the results chemometrically.

Journal Article↗
PubMed2000

Single-use phosphorimetric sensor for the determination of nalidixic acid in human urine and milk.

A single-use phosphorimetric sensor to determine the germicide nalidixic acid is proposed. The sensing action is based on the absorption of the analyte into the sensing zone and the subsequent measurement of the phosphorescence intensity emitted by the analyte fixed in the sensor. This plane drop sensor is made up of a 3 x 1.6 cm sheet of the polyester Mylar as solid support, and a circular film 5 mm in diameter and 20 microns in thickness, formed by poly(vinyl chloride) and tributyl phosphate as the plasticizer, adhered to its surface. The sensor is introduced for 2 h into the sample solution, after which it is dried and the phosphorescence intensity is measured directly at lambda ex = 332 nm, lambda em = 412 nm, with a delay time of 0.15 ms and a gate time of 10 ms, under a dry nitrogen stream. The characteristic parameters of the construction of the sensing zone and of the processes of fixing the analyte along with the emission of phosphorescence were studied. The applicable concentration range was from 60 to 1500 ng ml-1, with a detection limit of 20 ng ml-1 and a precision of 2% expressed as relative standard deviation. The method was applied to the determination of nalidixic acid in milk and human urine with recoveries ranging between 96.0 and 103.7%. The calibration process was carried out by applying a mathematical method of finite elements that expresses the analytical signal as a function of the analyte concentration and equilibration time between the sensor and the sample solution.

Anti-Infective Agents↗
PubMed1999

Determination of warfarin in waters and human plasma by solid-phase room-temperature transmitted phosphorescence.

A new method for the determination of warfarin in waters and human plasma using solid-phase room-temperature phosphorescence is proposed. The sample was spotted on Whatman No. 4 filter paper, together with iodide and NaOH solutions, after which it was dried and its transmitted phosphorescence intensity measured at 467 nm using two quartz plates to avoid the quenching effect produced by oxygen. The applicable concentration range went from 0.3 to 4.0 mg. L-1, and the detection and quantification limits were 0.08 and 0.28 mg. L-1 respectively. The precision of the method, as a relative standard deviation, was 2.3%. The method was applied in the determination of warfarin in human plasma and different types of water. The interferences produced by the albumin of the human plasma were eliminated by the addition of Na2SO4 saturated solution. Recoveries ranging between 93.0 and 109.0% in the case of water samples, and between 95.0 and 103.0% in the case of human plasma, were obtained. These results were compared with the results obtained by other methods.

Anticoagulants↗
PubMed1997

Simultaneous determination of the colorants sunset yellow FCF and quinoline yellow by solid-phase spectrophotometry using partial least squares multivariate calibration.

A method for the simultaneous determination of the colorants Sunset Yellow FCF and Quinoline Yellow using solid-phase spectrophotometry is proposed. The colorants were isolated in Sephadex DEAE A-25 gel at pH 5.0, the gel-colorants system was packed in a 1 mm silica cell and spectra were recorded between 400 and 600 nm against a blank. Statistical results were obtained by partial least squares (PLS) multivariate calibration. The optimized matrix by using the PLS-2 method enables the determination of the colorants in artificial mixtures and commercial soft drinks.

Azo Compounds↗
PubMed1996

Determination of warfarin at trace-levels in water by solid-phase spectrofluorimetry.

A new selective and sensitive spectrofluorimetric method for the determination of warfarin at trace levels (0.2-50.0 ng/ml) in water is proposed. Warfarin is fixed on Sephadex QAE A-25 gel (at pH = 7.0) and its fluorescence is measured directly in the solid-phase using a 1-mm silica cell at 312/385 nm with a detection/quantification limit of 0.06/0.2 ng/ml, a relative standard deviation of 2.3% and recoveries between 95 and 105%. The method is applied to the determination of warfarin residues in water.

Journal Article↗
PubMed1993

Determination of thiabendazole residues in waters by solid-phase spectrofluorometry.

A new, sensitive and simple spectrofluorometric method for the determination of thiabendazole (TBZ) residues was studied. TBZ on Sephadex G-15 gel, pH 4.70 acetate buffer, is fixed to give fluorescence. The fluorescence of the gel-TBZ system, packed in a 1-mm quartz cell was measured directly using a solid-surface attachment. The applicable concentration range was 1.5-10.0 ng.mL-1 with a relative standard deviation of 1.4% and a detection limit of 0.1 ng.mL-1. The method was applied to the determination of thiabendazole in natural, waste, sea, and residual waters (98-100% recovery). The method is more sensitive and selective than other methods described in the literature. The presence of other fluorescent pesticides (dichlone, carbaryl, morestan, o-phenylphenol) with similar spectral features (lambda exc and lambda em neighboring to excitation and emission wavelengths of the TBZ) did not cause interference.

Hydrogen-Ion Concentration↗
PubMed1989

Determination of acetoacetate in urine by solid-phase spectrophotometry.

A method for the determination of acetoacetate has been developed based on solid-phase spectrophotometry (SPS). The acetoacetate reacts with nitroprusside and glycine and the reaction product is sorbed on Dowex 1-X8 resin. The absorbance of the resin phase at 590 and 720 nm is measured directly. The calibration graph is linear up to 3.3 mg l-1 and the RSD is 1.9%. The detection limit is 7.6 micrograms l-1. The method has been applied to the determination of acetoacetate in normal and diabetic subjects' urine without pretreatment of the samples, and the results compared with those of 1H-NMR and homogeneous nitroprusside methods.

Acetoacetates↗