Biomedical subjects

Antonio Molina-Díaz

Publications and source records attributed to Antonio Molina-Díaz.

14 recordsLinked to original sources

PubMed2007

Identification of pesticide transformation products in food by liquid chromatography/time-of-flight mass spectrometry via "fragmentation-degradation" relationships.

The identification of transformation products of pesticides in foodstuffs is a crucial task difficult to tackle, due to the lack of standards and scarce information available. In this work, we describe a methodology for the identification and structural elucidation of pesticide transformation products in food. The proposed strategy is based on the use of liquid chromatography electrospray time-of-flight mass spectrometry (LC/TOFMS): accurate mass measurements of (molecule and fragment) ions of interest are used in order to establish relationships between fragmentation of the parent pesticides in the instrument (in-source CID fragmentation) and possible degradation products of these pesticides in food. Examples of this strategy showing the potential of LC/TOFMS to determine unknown pesticides in food are described in two different real samples, suggesting that pesticides often are transformed into degradation products in the same fashion that they are fragmented in the instrument. Using the proposed approach and without using standards a priori, based solely on accurate mass measurements of ions and "fragmentation-degradation" relationships, we have identified two parent pesticides (amitraz and malathion) along with six degradation products, m/z 253 (N,N'-bisdimethylphenylformamidine), 163 (N-2,4-dimethylphenyl-N-methyl formamidine), 150 (2,4-dimethylformamidine), and 122 (2,4-dimethylaniline) from amitraz, and m/z 317 and 303, due to ether hydrolysis of methyl and ethyl groups from malathion. Structures for these species were proposed, and the potential of the proposed approach was critically discussed.

Amidines↗

PubMed2006

Multicommutated flow-through optosensors implemented with photochemically induced fluorescence: determination of flufenamic acid.

This article describes a multicommutated flow injection-solid phase spectroscopy system implemented with photochemically induced fluorescence for the determination of flufenamic acid (FFA). A strongly fluorescent photoproduct is generated when FFA is irradiated online under UV light in a strong sulfuric medium. The photoproduct generated is retained on C(18) silica gel (which fills the detection area of the flow cell) and directly monitored on the active solid support at 258/442 nm (lambda(ex)/lambda(em)). After maximum signal recording, the sensing zone is regenerated by eluting the retained photoproduct with an appropriate H(2)SO(4)/MeOH solution. The sensor, completely automated, is based on the use of three-way solenoid valves conveniently operated by a homemade multicommutation software written in Java language. The system is calibrated at 10 and 60s for sampling time, showing detection limits of 1.28 x 10(-9) and 5.33 x 10(-10) molL(-1) and sampling rates of 38 and 28 h(-1), respectively, with relative standard deviations of 0.9 and 1.2%. The applicability of the method is demonstrated for the determination of FFA in human serum, human urine, and a pharmaceutical preparation without any pre-treatment. Good recovery levels were achieved between 90.5 and 103.7%.

Anti-Inflammatory Agents↗

PubMed2005

Rapid determination of diphenylamine residues in apples and pears with a single multicommuted fluorometric optosensor.

In this work, a single flow injection multicommuted system using solid-surface fluorescence spectroscopy has been explored for the determination of diphenylamine in apples and pears. The native fluorescence signal of diphenylamine retained on the solid support (C18 silica gel) was used for its determination (lambda(exc)/lambda(em) 291/372 nm). The sample treatment consists of a liquid-liquid extraction with acetonitrile followed by a cleanup step using primary-secondary amines. The use of a continuous flow assembly implementing multicommutation, based on a set of three-way solenoid valves controlled by appropriate software, provides the automatic control of sample, carrier, and eluting solution with remarkable advantages in relation to conventional flow injection approaches. Using an optimized sampling time, the proposed method was linear in the range 0.25-5 mg kg(-1) with a detection limit of 0.06 mg kg(-1) and RSD (percent) values better than 3%. The proposed method was successfully applied to the analysis of diphenylamine in different apple and pear samples fortified at different concentrations, and recoveries between 78 and 104% were found. The results obtained illustrate the usefulness of the proposed method for the screening and evaluation of postharvest treatment of crops possibly containing diphenylamine.

Diphenylamine↗

PubMed2005

Flow-through sensor with Fourier transform Raman detection for determination of sulfonamides.

A flow-through sensor system with Fourier transform (FT) Raman spectroscopy as detection technique is described. The molecular and structural information contained in Raman spectra together with the selective retention of the species of interest on the sorbent make the proposed methodology highly selective. The flow-through sensor allowed the direct quantitative determination of sulfathiazole and sulfamethoxazole in the presence of other species that are normally encountered with these analytes. The system used Sephadex QAE A-25 resin as packing material of a flow-through cell on which sulfonamides were temporarily retained. Samples were transported by a carrier solution of NaOH 10(-2) mol l(-1) (pH = 12), and 2 ml of a [NaCl (0.10 mol l(-1))/NaOH (10(-2) mol l(-1))] solution was employed as eluent. Using a sample volume of 1 ml, the analytical signal was linear in the range 0.5-7 g l(-1) and 0.5-10 g l(-1), for sulfathiazole and sulfamethoxazole, respectively. RSDs (%) lower than 4% were obtained for both analytes. The sensor was satisfactorily applied to several commercial pharmaceutical preparations for human and animals in different physical presentations, including capsules, syrup, tablets, powders, injectables and suspensions.

Flow Injection Analysis↗

PubMed2005

Searching for non-target chlorinated pesticides in food by liquid chromatography/time-of-flight mass spectrometry.

In this study the unique and most salient features of liquid chromatography/time-of-flight-mass spectrometry (LC/TOFMS) were applied for the identification of non-target chlorinated pesticides in complex food extracts 'a priori', i.e., without the use of standards. The combination of high sensitivity full-scan spectra incorporating accurate mass measurements (routinely better than 2 ppm accuracy) of the protonated molecules with the evidence from resolved isotopic clusters provides the ability to obtain a reduced number of possible elemental compositions (typically 1-2). Databases were then used to find the identity of the suspected species using the elemental composition as a searching criterion. The accurate mass and the generated elemental composition of characteristic fragment ions of the suspected species provide further evidence for the proposed species. With this approach we have identified the following chlorinated pesticides in different market-purchased fruit and vegetable extracts: Chlorotoluron (tomato), iprodione (apple), and procymidone (grapes). Finally, the confirmation and quantitation of these suspected species were successfully accomplished with standards. Other unknown compounds could be partially identified based on the data obtained within this study. As an example, a chlorinated species ('m/z 311') is discussed; the elemental composition and possible structures were proposed and the analytical potential, advantages and disadvantages of the proposed approach critically discussed.

Algorithms↗

PubMed2005

Direct monitoring of lipid oxidation in edible oils by Fourier transform Raman spectroscopy.

Fourier transform Raman spectroscopy has been used to investigate the chemical changes taking place during lipid oxidation in several edible oils. Oxidative degradation of six vegetable oils was accelerated by heating at 160 degrees C. Formation of aldehydes was detected, and saturated as well as alpha,beta-unsaturated aldehydes could be identified with the help of pure component spectra. The formation of conjugated double bond systems and the isomerisation of cis to trans double bonds was observed in the C=C stretching region and found to follow a distinct pattern for the different oils. It was possible to associate these differences to the fatty acid composition. The time-dependent intensity changes in certain Raman bands were compared to conventional parameters used to determine the extent of oxidation in oils, such as anisidine value and K(270), and showed good correlation.

Fatty Acids↗

PubMed2004

Discrimination of olives according to fruit quality using Fourier transform Raman spectroscopy and pattern recognition techniques.

Fourier transform Raman spectroscopy combined with pattern recognition has been used to discriminate olives of different qualities. They included samples of sound olives, olives with frostbite, olives that have been collected from the ground, fermented olives, and olive samples with diseases. Milled olives were measured in a dedicated sample cup, which was rotated during spectrum acquisition. A preliminary study of the data set structure was performed using hierarchical cluster analysis and principal component analysis. Two supervised pattern recognition techniques, K-nearest neighbors and soft independent modeling of class analogy (SIMCA), were tested using a "leave-a-fourth-out" cross-validation procedure. SIMCA provided the best results, with prediction abilities of 95% for sound, 93% for frostbite, 96% for ground, and 92% for fermented olives. The olive samples with diseases (too few to define a class) were included in the validation and recognized as not belonging to any class. None of the damaged olive samples was wrongly predicted to the class of sound olives. With this approach a selection of sound olives for the production of high-quality virgin olive oil can be achieved.

Fourier Analysis↗

PubMed2004

Development of a single fluorescence-based optosensor for rapid simultaneous determination of fungicides benomyl and thiabendazole in waters and commercial formulations.

A novel, sensitive, and straightforward spectrofluorimetric flow injection method is proposed in this work for the resolution of a binary mixture of two widely used fungicides (thiabendazole and benomyl). The continuous flow methodology is based on the implementation of on-line solid phase extraction (SPE), preconcentration, and separation of both analytes on a surface of C(18) silica gel beads placed just in the flow cell, with solid surface fluorescence detection. A 45- and 25-fold sensitivity enhancement was obtained for benomyl and thiabendazole, respectively (in relation to the liquid phase measurements in the absence of solid support). The separation of the pesticides was performed because of the different retention-desorption kinetics in their interaction with the solid support, in the zone where the stream impinges the solid material. No previous separation of the analytes before they reach the flow cell is needed, simplifying extraordinarily both the procedure and the manifold. Using a sample volume of 3200 microL, the system was calibrated in the range of 0.4-20 and 20-400 ng x mL(-)(1) with detection limits of 0.06 and 3.6 ng x mL(-)(1) for thiabendazole and benomyl, respectively, and RSD values (n = 10) smaller than 0.8% for both analytes. The RSD values obtained replacing the solid support in each measurement were lower than 3%, and the day-to-day reproducibility RSD value was also lower than 5%. Sampling frequencies of 10 and 18 h(-)(1) were obtained with 600 and 3200 microL of sample volume. Recovery studies carried out on natural water samples spiked with known amounts of both analytes at concentration levels in the range of 1-10 and 25-200 ng x mL(-)(1) provided mean recovery percentages ranging from 98.8 to 102% and from 98 to 103% for thiabendazole and benomyl, respectively. The proposed methodology was also applied to pesticide formulations.

Benomyl↗

PubMed2004

Determination of oil and water content in olive pomace using near infrared and Raman spectrometry. A comparative study.

Near infrared (NIR) reflectance and Raman spectrometry were compared for determination of the oil and water content of olive pomace, a by-product in olive oil production. To enable comparison of the spectral techniques the same sample sets were used for calibration (1.74-3.93% oil, 48.3-67.0% water) and for validation (1.77-3.74% oil, 50.0-64.5% water). Several partial least squares (PLS) regression models were optimized by cross-validation with cancellation groups, including different spectral pretreatments for each technique. Best models were achieved with first-derivative spectra for both oil and water content. Prediction results for an independent validation set were similar for both techniques. The values of root mean square error of prediction (RMSEP) were 0.19 and 0.20-0.21 for oil content and 2.0 and 1.8 for water content, using Raman and NIR, respectively. The possibility of improving these results by combining the information of both techniques was also tested. The best models constructed using the appended spectra resulted in slightly better performance for oil content (RMSEP 0.17) but no improvement for water content.

Least-Squares Analysis↗

PubMed2003

Fourier transform Raman spectrometry for the quantitative analysis of oil content and humidity in olives.

A method for the direct and fast determination of oil content and humidity in olives using Fourier transform Raman spectrometry is reported. The only sample preparation step required was crushing of the olives using a hammer mill. The crushed olives were placed in a dedicated sample cup, which was rotated excentrically to the horizontal laser beam during spectrum acquisition. This allowed us to sample an increased volume and thus compensate for sample inhomogeneities. In this way the reproducibility of Raman spectra taken from crushed olives was significantly improved. Partial least-squares (PLS) regression was used for the chemometric evaluation of the Raman spectra. Standard errors of prediction for the validation set of 0.81% for oil content (in the range 19.68-35.71%) and 1.54% for humidity (in the range 29.23-51.49%), both expressed as weight percentage referred to fresh matter, were obtained.

Food Analysis↗

PubMedDate not supplied

Use of a continuous flow solid-phase spectroscopic sensor using two sensing zones: determination of thiamine and ascorbic acid.

A simple, rapid, inexpensive, and automated flow-through solid-phase spectroscopic sensing device is proposed for the sequential determination of 2 vitamins: thiamine and ascorbic acid. The vitamins are concentrated on ion-exchange gels, thiamine on Sephadex SP C-25, and ascorbic acid on Sephadex QAE A-25; both solid supports are packed in 2 different flow cells. The absorbance is monitored directly on the solid phase with a double-beam spectrophotometer at 250 nm, without derivatization or additional elution. With the use of 2 carrier/self-eluting solutions (0.1 5M sodium acetate/acetic acid and 0.18M citric acid/K2HPO4) and a sample volume of 1000 microL, the sensor responds linearly in the range of 0.5-15 and 3-50 microg/mL with detection limits of 0.14 and 0.36 microg/mL for thiamine and ascorbic acid, respectively. When the method was applied to synthetic samples and pharmaceutical preparations, precise and accurate values were obtained.

Ascorbic Acid↗

PubMedDate not supplied

Simultaneous determination of codeine and pyridoxine in pharmaceutical preparations by first-derivative spectrofluorimetry.

A method for the simultaneous determination of codeine and pyridoxine was developed, based on the measurement of their native fluorescence signals, by using first-derivative spectrofluorimetry to resolve the mixture. Codeine was measured at lambda(em) = 309 nm, and pyridoxine was measured at lambda(em) = 450 nm. Instrumental parameters were optimized, and the emission spectra were recorded between 275 and 475 nm, at lambda(ex) = 255 nm and excitation and emission slit widths of 2.5 and 10 nm, respectively. Systematic studies on the influence of species usually present along with the analytes (such as caffeine, ascorbic acid, paracetamol, and thiamine) were also performed. The calibration graphs were linear over the ranges of 0.5-7.0 and 0.1-1.0 microg/mL for codeine and pyridoxine, respectively, and the relative standard deviations (n = 10) were about 3%. The method was successfully applied to the determination of codeine and pyridoxine in solutions of synthetic mixtures and in synthetic and semisynthetic pharmaceutical formulations.

Chemistry Techniques, Analytical↗

PubMedDate not supplied

Determination of ciprofloxacin with a room-temperature phosphorescence flow-through sensor based on lanthanide-sensitized luminescence.

Direct measurement of the sensitized luminescence of the europium-ciprofloxacin chelate immobilized on a cationic exchanger was used to develop a flow-through room-temperature phosphorescence optosensor for determination of ciprofloxacin. The phosphorescent chelate is formed on-line at room temperature in a flow-injection system and is immobilized on a weakly acidic cation-exchange resin packed in a flow cell. Optimum experimental conditions and analytical performance are discussed in detail. The sensor response for ciprofloxacin was linear, from 1.5 x 10(-6) to 2.0 x 10(-5)M with a relative standard deviation of 2.5% (n = 10) and a detection limit of 1.1 x 10(-7)M. The effect of possible interferences on sensor response was studied. The sensor was successfully tested for the determination of ciprofloxacin in pharmaceutical formulations.

Anti-Infective Agents↗

PubMedDate not supplied

Flow-through fluorescence-based optosensor with on-line solid-phase separation for the simultaneous determination of a ternary pesticide mixture.

A rapid and selective method was developed for the simultaneous determination of 3 widely used pesticides, carbendazim (CBZ), carbofuran (CF), and benomyl (BNM). The method utilized a single continuous-flow, solid surface fluorometric multioptosensor implemented with a previous separation of the analytes on a minicolumn, placed just before the sensor, that was packed with the same solid support (C18 silica gel) as the flow-through cell. The separation was achieved because of the different kinetics of retention/elution of the pesticides on the solid support in the minicolumn, enabling the sequential arrival of the analytes at the sensing zone. With a single injection of the mixture, 2 of them were more strongly retained in the minicolumn (CF and BNM) while the other (CBZ) passed through the system towards the sensing material where it developed its fluorescence transitory signal. Then, CF and BNM were successively eluted from the solid support using 2 different eluting solutions, and they sequentially reached the sensing zone and developed their respective signals. A multiwavelength fluorescence detection mode was used, recording the signals of each pesticide at its maximum excitation/emission wavelength; therefore, the sensitivity was increased. The system was calibrated using a sample volume of 2000 microL. The linear dynamic range was 80-1400, 250-2400, and 150-2000 ng/mL with detection limits of 15, 68, and 35 ng/mL and relative standard deviation values of 3.5, 3.2, and 2.4% for CBZ, CF, and BNM, respectively. A recovery study was applied to spiked environmental water samples, and recoveries ranged from 96 to 104%.

Air Pollutants, Occupational↗