Marcela Segundo - Academia.edu (original) (raw)

Papers by Marcela Segundo

Analytica Chimica Acta, 2002

The performance of sequential injection (SI) systems has often been criticized for its low sampli... more The performance of sequential injection (SI) systems has often been criticized for its low sampling frequency. The present work describes a SI system where an injection valve and an additional pump were incorporated to enhance sample throughput rate. The proposed system was applied to the enzymatic determination of glycerol and ethanol in wines, using spectrophotometric detection and immobilized glycerol and alcohol dehydrogenases. The method proposed was applied to the determination of ethanol between 0.10 and 0.50% (v/v) and glycerol between 0.03 and 0.30 g l −1 . These ranges were appropriate for determination in table and port wines, since samples were diluted 50 times before introduction into the system. The results obtained from 15 wine samples were statistically comparable to those obtained by the reference methods, with good repeatability (R.S.D. < 3.4%, n = 10). The sampling rate was 22.5 h −1 , corresponding to 45 determinations per hour. This way, the time required for each determination was decreased by 30% when compared to a conventional SI system.

Talanta, 2010

In the present work, a rapid and high-throughput Folin-Ciocalteu (F-C) reducing capacity assay ad... more In the present work, a rapid and high-throughput Folin-Ciocalteu (F-C) reducing capacity assay adapted to routine/screening analysis was developed. In order to attain a fast F-C reducing kinetic reaction, the reaction conditions of the classical time-consuming F-C assay were modified and the influence of alkali and F-C reagent concentration was evaluated using gallic acid as standard. The proposed method was performed in a 96-well microplate format and it was applied to several phenolic compounds and food products (wines, beers, infusions and juices) providing F-C reducing capacity results after 3 min of reaction similar to those obtained by the time-consuming (120 min) conventional method. The additive and synergistic effect of reducing nonphenolic compounds usually found in food samples was also investigated. Ascorbic acid and ferrous sulfate provided an additive effect, while for fructose, glucose and sodium sulfite a synergistic effect was obtained. The detection limit was 0.25 mg L −1 (as gallic acid) and the repeatability was <1.6% (n = 12).

Talanta, 2009

In this work a fast, automatic solid-phase extraction procedure hyphenated to HPLC-UV is proposed... more In this work a fast, automatic solid-phase extraction procedure hyphenated to HPLC-UV is proposed for screening of priority phenolic pollutants in waters at ng mL −1 levels. A flow through column, containing polystyrene-divinylbenzene sorbent, was incorporated to a multisyringe flow injection system (MSFIA), where the sample loading and analyte elution were carried out after computer control. The MSFIA system also directed the eluent to fill the injection loop of the chromatograph, coupling the sample preparation to its determination. High enrichment factors were attained for phenol and ten of its derivatives (mean value 176 for 50 mL of sample), with LOD values lower than 1 ng mL −1 for the maximum volume of sample used (100 mL). For all analytes, mean recoveries between 89 and 103% were obtained for different water matrices. Certified reference material and a contaminated soil (RTC-CRM 112) were also tested successfully. The determination frequency was 4-10 h −1 , providing an automatic, fast and reliable tool for water quality and environmental monitoring.

Analytical Sciences, 2008

The present work explores the slurry sampling approach for automatic, flow-based plant analysis. ... more The present work explores the slurry sampling approach for automatic, flow-based plant analysis. For this purpose, pinch valves were introduced into a multi-syringe flow injection analysis manifold to provide the repeatable aspiration of a few microliters of plant suspension before the material was further processed through the flow system. For validation of the proposed approach, the determination of potassium by flame emission spectrometry was implemented. Several parameters were studied: the concentration of plant particles in the sample suspension and the utilization of matrix modifiers. Microwave digestion was also implemented; no significant difference was found when certified reference material was analyzed with or without the in-line digestion step. The system was successfully applied to 13 samples within a concentration range of 2.5 to 100 mg g(-1). A determination frequency of 28 h(-1) was achieved and the precision was better than 4.0% (n = 12).

Analytical Chemistry, 2007

In the present work, a chemiluminometric automatic flow methodology for the in vitro determinatio... more In the present work, a chemiluminometric automatic flow methodology for the in vitro determination of hypochlorous acid scavenging capacity, under pH and concentration conditions similar to those found in vivo, is proposed. As the pH found in physiological conditions (7.4) and the pH required for the chemiluminescence detection reaction (>10) are different, the multisyringe flow injection analysis features were exploited to perform the in-line reaction of HOCl and the scavenger molecule at physiological pH prior to reaction of the remaining HOCl with luminol at alkaline conditions. These two reactions were carried out in about 3 s, allowing the determination of fast reacting antioxidants, in a time frame closer to in vivo generation of HOCl when compared to previously described methods. The developed method was applied to nonsteroidal antiinflammatory drugs of different chemical families, and positive controls (cysteine, gallic acid, lipoic acid). The HOCl scavenging capacity was evaluated at pH 7.4 and 10.0; different results were found for oxicam derivatives, providing evidence that the pH of in vitro methods should be carefully selected to allow assumptions about putative in vivo effects.

Mikrochimica Acta, 2005

A multi-syringe flow injection system for the determination of total phenolics based on the 4-ami... more A multi-syringe flow injection system for the determination of total phenolics based on the 4-aminoantipyrine reaction is proposed. In-line preconcentration using solid-phase extraction was implemented, offering an environmentally friendly alternative to organic solvent extraction performed in the batch procedure and in previously described flow methodologies. Therefore, phenolic compounds were retained in Amberlite XAD4 resin using acidic conditions. The elution was carried out using 0.10 mol L−1 NaOH solution, promoting the ionisation of the retained phenolic compounds, and thus their desorption. Since different elution profiles were obtained for several phenol derivatives, the calibration curves were established using the peak area as analytical signal. Moreover, a dynamic calibration range was applied by using a variable sample volume (0.500–6.00 mL) and calibration curves based on the mass of phenol retained in the pre-concentration column. A methodology based on a fixed sample volume (24.0 mL) was also proposed for determination at concentration levels below 50 µg L−1. A limit of detection of 52 ng of phenol (9 or 2 µg L−1) was achieved with a sampling frequency of 10–16 h−1 for the variable volume method and 4 h−1 for the fixed volume method. The application of the proposed methodology to reference material provided results that were within the certified acceptance limits.

Trends in Analytical Chemistry, 2009

Conventionally, measuring antioxidant capacity is time consuming, laborious and costly, especiall... more Conventionally, measuring antioxidant capacity is time consuming, laborious and costly, especially in routine work. These limitations can be overcome using multi-syringe flow-injection analysis (MSFIA), which has succeeded in automating the most widely applied antioxidant-capacity assays that use chromogen radicals or reactive species found in vivo. We highlight the features of MSFIA and improved methodologies in using MSFIA to measure antioxidant capacity. ª

Talanta, 2009

Redox reactions are the heart of numerous biochemical pathways found in cellular chemistry, gener... more Redox reactions are the heart of numerous biochemical pathways found in cellular chemistry, generating reactive oxygen species (ROS) and reactive nitrogen species (RNS), that includes superoxide anion radical (O 2

Analytical Chemistry, 2010

Molecular imprinted polymers (MIP) have recently drawn much attention as highly selective solid-p... more Molecular imprinted polymers (MIP) have recently drawn much attention as highly selective solid-phase materials for handling and isolation of organic pollutants in complex matrices. Because of the impaired retention capacity for target species as compared with reversed-phase materials and irreversible sorption of interfering compounds by nonspecific interactions, the implementation of MIPbased solid-phase reactors as permanent components in automatic flow-systems has not received widespread acceptance as of yet. To tackle this limitation, a dynamic microscale solid phase extraction (µSPE) method capitalizing on the principle of programmable flow and bead injection analysis is herein proposed as a front end to liquid chromatography for multiresidue assays. It involves in-line renewable tandem-SPE microcolumns composed of molecularly imprinted polymers and copolymeric Nvinylpyrrolidone/divinylbenzene beads integrated within the flow network for multimodal extraction. Chlorotriazine herbicides (namely, atrazine, simazine, propazine) and principal degradation products thereof (namely, deisopropylatrazine and deethylatrazine) were selected as model analytes. The effect of several parameters, including the dimensions and chemical composition of the sorptive microcolumns, the sample loading flow rate, the type and volume of eluent, the interface with liquid chromatography (LC), and the disposable nature of the column on the analytical performance were investigated in detail. The assembled flow setup features appropriate removal of interfering organic species via solvent switch with toluene, the circumvention of analyte band-broadening in LC by in-line merging of the eluate with a water stream, and the transfer of the overall analyte-containing eluate into the LC. For 10-mL sample percolation, limits of detection (S/N ) 3) of 0.02-0.04 ng mL -1 , limits of quantification (S/N ) 10) of 0.07-0.12 ng mL -1 , absolute recovery percentages >79%, precision within 1.4-5.5%, and enrichment factors of 46-49 were obtained for the suite of assayed herbicides. The multimodal µSPE method with renewable beads was applied to the multiresidue determination of the target herbicides in crude soil extracts and untreated environmental waters at concentration levels below those endorsed by the current EU Water Framework Directives following appropriate sample preconcentration and/or cleanup.

Journal of Agricultural and Food Chemistry, 2006

A sequential injection system for the automatic determination of glycerol in wine and beer was de... more A sequential injection system for the automatic determination of glycerol in wine and beer was developed. The method is based on the rate of formation of NADH from the reaction of glycerol and NAD+ catalyzed by the enzyme glycerol dehydrogenase in solution. The determination of glycerol was performed between 0.3 and 3.0 mmol L(-1) (0.028 and 0.276 g L(-1)), and good repeatability was attained (rsd &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 3.6%, n = 5) for all samples tested. The determination rate was 54 h(-1), the reagent consumption was only 0.75 micromol of NAD+ and 5.4 ng of enzyme per assay, and the waste production was 2.12 mL per assay. Results obtained for samples were in agreement with those obtained with the batch enzymatic method.

Analytica Chimica Acta, 2007

In the present work, an automatic flow procedure for the sequential spectrophotometric determinat... more In the present work, an automatic flow procedure for the sequential spectrophotometric determination of Folin-Ciocalteu reducing capacity (FC assay) and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS •+ ) scavenging capacity expressed as the trolox equivalent (TEAC assay) is proposed for a comparative study of antioxidant properties in food products. Exploiting the flexibility of flow management associated to the computer control offered by multisyringe flow injection analysis, both methodologies were carried out in the same manifold using gallic acid and trolox as standard compounds. The proposed system configuration allowed the performance of each method separately or in tandem, providing 24 determinations per hour, which accounts for its application in routine analysis.

Analytica Chimica Acta, 2007

Please cite this article as: M. Manera, M. Miró, J.M. Estela, V. Cerdà, M.A. Segundo, J.L.F.C. Li... more Please cite this article as: M. Manera, M. Miró, J.M. Estela, V. Cerdà, M.A. Segundo, J.L.F.C. Lima, Flow-through solid-phase reflectometric method for simultaneous multiresidue determination of nitrophenol derivatives, Analytica Chimica Acta (2007), Abstract In this paper, a flow-through optosensor based on diffuse reflectance spectroscopy and multivariate regression modelling is proposed for simultaneous multiresidue determination of trace level concentrations of nitro-substituted phenols. The optrode integrates on-line anion-exchange sorptive preconcentration and matrix removal with direct detection of sorbed species onto the sensing layer and chemometric deconvolution of overlapped spectra. After recording of the reflectometric spectrum, fast chemosensor regeneration is accomplished with an acidic methanolic eluent followed by a metered volume of alkaline solution. The full automation of the analytical procedure is ensured by flow-programming as executed via a software-controlled multisyringe pump and a set of multiposition and solenoid valves.

Talanta, 2004

A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line... more A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on the MWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D. < 2.41%) and determination frequency of 12 h −1 were obtained.

International Journal of Environmental Analytical Chemistry, 2005

Considering the importance of monitoring the levels of nutrients present in soils and their avail... more Considering the importance of monitoring the levels of nutrients present in soils and their availability to plants, an automatic methodology is proposed based on multi-syringe flow injection analysis (MSFIA) for the spectrophotometric determination of available ...

Talanta, 2000

A sequential injection system for the spectrophotometric determination of reducing sugars in wine... more A sequential injection system for the spectrophotometric determination of reducing sugars in wines is described. The methodology is based on the formation of a coloured complex produced by the reaction of copper (I) with 2,9-dimethyl-1,10-phenanthroline (neocuproine), after reduction of copper (II) to copper (I) by reducing sugars. In the present SI system, a dialysis unit was incorporated not only to allow the sample dilution, but also to minimise the interference of some coloured compounds. In this way, direct sample introduction into the system was possible, without any previous treatment of the wine samples. The proposed method can be applied to the determination of reducing sugars in two concentration ranges: from 2 to 25 g l − 1 (table wines) and from 20 to 140 g l − 1 (Port wines). To perform determinations in these two ranges, the manifold configuration remained the same; just a few operational parameters were changed in the controlling software. A sampling-rate of 14 -18 samples per hour was obtained with good repeatability for ten consecutive injections of wine samples (relative standard deviations (RSD) B2.1%). The results obtained from 19 wine samples were comparable to those obtained by the reference method.

Analytica Chimica Acta, 2001

In the present work, a sequential injection system with spectrophotometric detection was develope... more In the present work, a sequential injection system with spectrophotometric detection was developed for the determination of free and total sulphur dioxide in wines. It was based on the formation of a coloured product from the reaction among SO 2 , formaldehyde and pararosaniline. A gas diffusion unit (GDU) was incorporated into the manifold to prevent the wine matrix interference in the spectrophotometric measurement. An acid solution was added to the sample prior to its passage through the donor channel of the GDU to promote gaseous SO 2 formation. For the free SO 2 determination, the sample was directly aspirated into the holding coil; for the total SO 2 determination, the sample was processed after previous in-line hydrolysis of bound SO 2 with an alkali solution.

Microchemical Journal, 2006

A multi-syringe flow injection system for the potentiometric determination of exchangeable potass... more A multi-syringe flow injection system for the potentiometric determination of exchangeable potassium in soil samples is proposed. Firstly, a manifold was devised to allow determination in soil extracts prepared off-line. It was possible to analyze samples ...

Analytica Chimica Acta, 2006

In the present work, an automatic method based on multi-syringe flow injection analysis (MSFIA) w... more In the present work, an automatic method based on multi-syringe flow injection analysis (MSFIA) was developed for the determination of total antioxidant capacity, measured as the cumulative capacity of the compounds present in the sample to scavenge free radicals, using the 2,2-diphenyl-1-picrylhydrazyl (DPPH • ) reaction. The determination is based on the colour disappearance due to the scavenging of DPPH • by antioxidant compounds monitored spectrophotometrically at 517 nm.

Analytica Chimica Acta, 2005

In multi-syringe flow injection analysis (MSFIA), devices as selection, injection or commutation ... more In multi-syringe flow injection analysis (MSFIA), devices as selection, injection or commutation valves must be incorporated to the manifold to provide access to sample and standard solutions. Therefore, the definition of sample amount can be either volume or time-based. In the present work, four configurations for sample introduction (two for each approach) were tested in order to establish if the different strategies affect the analytical signal in MSFIA systems. The mean absorbance value from ten consecutive injections of a bromothymol blue solution obtained for the time-based strategy was lower than that provided by the volume-based approach as the exact volume delivered by each configuration was different from the "theoretical" volume. For time-based configurations, the exact volume delivered is 2-5% lower than the theoretical value while for volume-based configurations, the volume delivered was between 6 and 46% larger than the theoretical volume. Moreover, for time-based sampling, the order of steps in the analytical cycle was of utmost importance since any alteration in the flow direction affected the volume delivered in the subsequent step in the analytical cycle. The influence of the two sampling approaches was also evaluated in the MSFIA systems for the spectrophotometric determination of phenolic compounds and the potentiometric determination of chloride. There was no evidence that the use of either volume or time-based sampling would improve the analytical features of these determinations when real samples were tested.

Journal of Agricultural and Food Chemistry, 2006

In the present work, an automatic flow procedure based on multi-syringe flow injection analysis w... more In the present work, an automatic flow procedure based on multi-syringe flow injection analysis was developed for the assessment of Folin-Ciocalteu reagent (FCR) reducing capacity in several types of food products using gallic acid as the standard. Different strategies for mixing of sample and reagent were tested (continuous flow of FCR, merging zones, and intercalated zones approaches); lower reagent consumption and higher determination throughput were attained for the merging zones approach (100 µL of sample + 100 µL of FCR). The application of the proposed method to compounds with known antioxidant activity (both phenolic and nonphenolic) and to samples (wines, beers, teas, soft drinks, and fruit juices) provided results similar to those obtained by the conventional batch method. The detection limit was 0.6 mg L -1 , and the determination frequency was about 12 h -1 . Good repeatability was attained (RSD < 1.3%, n ) 10).

Analytica Chimica Acta, 2002

The performance of sequential injection (SI) systems has often been criticized for its low sampli... more The performance of sequential injection (SI) systems has often been criticized for its low sampling frequency. The present work describes a SI system where an injection valve and an additional pump were incorporated to enhance sample throughput rate. The proposed system was applied to the enzymatic determination of glycerol and ethanol in wines, using spectrophotometric detection and immobilized glycerol and alcohol dehydrogenases. The method proposed was applied to the determination of ethanol between 0.10 and 0.50% (v/v) and glycerol between 0.03 and 0.30 g l −1 . These ranges were appropriate for determination in table and port wines, since samples were diluted 50 times before introduction into the system. The results obtained from 15 wine samples were statistically comparable to those obtained by the reference methods, with good repeatability (R.S.D. < 3.4%, n = 10). The sampling rate was 22.5 h −1 , corresponding to 45 determinations per hour. This way, the time required for each determination was decreased by 30% when compared to a conventional SI system.

Talanta, 2010

In the present work, a rapid and high-throughput Folin-Ciocalteu (F-C) reducing capacity assay ad... more In the present work, a rapid and high-throughput Folin-Ciocalteu (F-C) reducing capacity assay adapted to routine/screening analysis was developed. In order to attain a fast F-C reducing kinetic reaction, the reaction conditions of the classical time-consuming F-C assay were modified and the influence of alkali and F-C reagent concentration was evaluated using gallic acid as standard. The proposed method was performed in a 96-well microplate format and it was applied to several phenolic compounds and food products (wines, beers, infusions and juices) providing F-C reducing capacity results after 3 min of reaction similar to those obtained by the time-consuming (120 min) conventional method. The additive and synergistic effect of reducing nonphenolic compounds usually found in food samples was also investigated. Ascorbic acid and ferrous sulfate provided an additive effect, while for fructose, glucose and sodium sulfite a synergistic effect was obtained. The detection limit was 0.25 mg L −1 (as gallic acid) and the repeatability was <1.6% (n = 12).

Talanta, 2009

In this work a fast, automatic solid-phase extraction procedure hyphenated to HPLC-UV is proposed... more In this work a fast, automatic solid-phase extraction procedure hyphenated to HPLC-UV is proposed for screening of priority phenolic pollutants in waters at ng mL −1 levels. A flow through column, containing polystyrene-divinylbenzene sorbent, was incorporated to a multisyringe flow injection system (MSFIA), where the sample loading and analyte elution were carried out after computer control. The MSFIA system also directed the eluent to fill the injection loop of the chromatograph, coupling the sample preparation to its determination. High enrichment factors were attained for phenol and ten of its derivatives (mean value 176 for 50 mL of sample), with LOD values lower than 1 ng mL −1 for the maximum volume of sample used (100 mL). For all analytes, mean recoveries between 89 and 103% were obtained for different water matrices. Certified reference material and a contaminated soil (RTC-CRM 112) were also tested successfully. The determination frequency was 4-10 h −1 , providing an automatic, fast and reliable tool for water quality and environmental monitoring.

Analytical Sciences, 2008

The present work explores the slurry sampling approach for automatic, flow-based plant analysis. ... more The present work explores the slurry sampling approach for automatic, flow-based plant analysis. For this purpose, pinch valves were introduced into a multi-syringe flow injection analysis manifold to provide the repeatable aspiration of a few microliters of plant suspension before the material was further processed through the flow system. For validation of the proposed approach, the determination of potassium by flame emission spectrometry was implemented. Several parameters were studied: the concentration of plant particles in the sample suspension and the utilization of matrix modifiers. Microwave digestion was also implemented; no significant difference was found when certified reference material was analyzed with or without the in-line digestion step. The system was successfully applied to 13 samples within a concentration range of 2.5 to 100 mg g(-1). A determination frequency of 28 h(-1) was achieved and the precision was better than 4.0% (n = 12).

Analytical Chemistry, 2007

In the present work, a chemiluminometric automatic flow methodology for the in vitro determinatio... more In the present work, a chemiluminometric automatic flow methodology for the in vitro determination of hypochlorous acid scavenging capacity, under pH and concentration conditions similar to those found in vivo, is proposed. As the pH found in physiological conditions (7.4) and the pH required for the chemiluminescence detection reaction (>10) are different, the multisyringe flow injection analysis features were exploited to perform the in-line reaction of HOCl and the scavenger molecule at physiological pH prior to reaction of the remaining HOCl with luminol at alkaline conditions. These two reactions were carried out in about 3 s, allowing the determination of fast reacting antioxidants, in a time frame closer to in vivo generation of HOCl when compared to previously described methods. The developed method was applied to nonsteroidal antiinflammatory drugs of different chemical families, and positive controls (cysteine, gallic acid, lipoic acid). The HOCl scavenging capacity was evaluated at pH 7.4 and 10.0; different results were found for oxicam derivatives, providing evidence that the pH of in vitro methods should be carefully selected to allow assumptions about putative in vivo effects.

Mikrochimica Acta, 2005

A multi-syringe flow injection system for the determination of total phenolics based on the 4-ami... more A multi-syringe flow injection system for the determination of total phenolics based on the 4-aminoantipyrine reaction is proposed. In-line preconcentration using solid-phase extraction was implemented, offering an environmentally friendly alternative to organic solvent extraction performed in the batch procedure and in previously described flow methodologies. Therefore, phenolic compounds were retained in Amberlite XAD4 resin using acidic conditions. The elution was carried out using 0.10 mol L−1 NaOH solution, promoting the ionisation of the retained phenolic compounds, and thus their desorption. Since different elution profiles were obtained for several phenol derivatives, the calibration curves were established using the peak area as analytical signal. Moreover, a dynamic calibration range was applied by using a variable sample volume (0.500–6.00 mL) and calibration curves based on the mass of phenol retained in the pre-concentration column. A methodology based on a fixed sample volume (24.0 mL) was also proposed for determination at concentration levels below 50 µg L−1. A limit of detection of 52 ng of phenol (9 or 2 µg L−1) was achieved with a sampling frequency of 10–16 h−1 for the variable volume method and 4 h−1 for the fixed volume method. The application of the proposed methodology to reference material provided results that were within the certified acceptance limits.

Trends in Analytical Chemistry, 2009

Conventionally, measuring antioxidant capacity is time consuming, laborious and costly, especiall... more Conventionally, measuring antioxidant capacity is time consuming, laborious and costly, especially in routine work. These limitations can be overcome using multi-syringe flow-injection analysis (MSFIA), which has succeeded in automating the most widely applied antioxidant-capacity assays that use chromogen radicals or reactive species found in vivo. We highlight the features of MSFIA and improved methodologies in using MSFIA to measure antioxidant capacity. ª

Talanta, 2009

Redox reactions are the heart of numerous biochemical pathways found in cellular chemistry, gener... more Redox reactions are the heart of numerous biochemical pathways found in cellular chemistry, generating reactive oxygen species (ROS) and reactive nitrogen species (RNS), that includes superoxide anion radical (O 2

Analytical Chemistry, 2010

Molecular imprinted polymers (MIP) have recently drawn much attention as highly selective solid-p... more Molecular imprinted polymers (MIP) have recently drawn much attention as highly selective solid-phase materials for handling and isolation of organic pollutants in complex matrices. Because of the impaired retention capacity for target species as compared with reversed-phase materials and irreversible sorption of interfering compounds by nonspecific interactions, the implementation of MIPbased solid-phase reactors as permanent components in automatic flow-systems has not received widespread acceptance as of yet. To tackle this limitation, a dynamic microscale solid phase extraction (µSPE) method capitalizing on the principle of programmable flow and bead injection analysis is herein proposed as a front end to liquid chromatography for multiresidue assays. It involves in-line renewable tandem-SPE microcolumns composed of molecularly imprinted polymers and copolymeric Nvinylpyrrolidone/divinylbenzene beads integrated within the flow network for multimodal extraction. Chlorotriazine herbicides (namely, atrazine, simazine, propazine) and principal degradation products thereof (namely, deisopropylatrazine and deethylatrazine) were selected as model analytes. The effect of several parameters, including the dimensions and chemical composition of the sorptive microcolumns, the sample loading flow rate, the type and volume of eluent, the interface with liquid chromatography (LC), and the disposable nature of the column on the analytical performance were investigated in detail. The assembled flow setup features appropriate removal of interfering organic species via solvent switch with toluene, the circumvention of analyte band-broadening in LC by in-line merging of the eluate with a water stream, and the transfer of the overall analyte-containing eluate into the LC. For 10-mL sample percolation, limits of detection (S/N ) 3) of 0.02-0.04 ng mL -1 , limits of quantification (S/N ) 10) of 0.07-0.12 ng mL -1 , absolute recovery percentages >79%, precision within 1.4-5.5%, and enrichment factors of 46-49 were obtained for the suite of assayed herbicides. The multimodal µSPE method with renewable beads was applied to the multiresidue determination of the target herbicides in crude soil extracts and untreated environmental waters at concentration levels below those endorsed by the current EU Water Framework Directives following appropriate sample preconcentration and/or cleanup.

Journal of Agricultural and Food Chemistry, 2006

A sequential injection system for the automatic determination of glycerol in wine and beer was de... more A sequential injection system for the automatic determination of glycerol in wine and beer was developed. The method is based on the rate of formation of NADH from the reaction of glycerol and NAD+ catalyzed by the enzyme glycerol dehydrogenase in solution. The determination of glycerol was performed between 0.3 and 3.0 mmol L(-1) (0.028 and 0.276 g L(-1)), and good repeatability was attained (rsd &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 3.6%, n = 5) for all samples tested. The determination rate was 54 h(-1), the reagent consumption was only 0.75 micromol of NAD+ and 5.4 ng of enzyme per assay, and the waste production was 2.12 mL per assay. Results obtained for samples were in agreement with those obtained with the batch enzymatic method.

Analytica Chimica Acta, 2007

In the present work, an automatic flow procedure for the sequential spectrophotometric determinat... more In the present work, an automatic flow procedure for the sequential spectrophotometric determination of Folin-Ciocalteu reducing capacity (FC assay) and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS •+ ) scavenging capacity expressed as the trolox equivalent (TEAC assay) is proposed for a comparative study of antioxidant properties in food products. Exploiting the flexibility of flow management associated to the computer control offered by multisyringe flow injection analysis, both methodologies were carried out in the same manifold using gallic acid and trolox as standard compounds. The proposed system configuration allowed the performance of each method separately or in tandem, providing 24 determinations per hour, which accounts for its application in routine analysis.

Analytica Chimica Acta, 2007

Please cite this article as: M. Manera, M. Miró, J.M. Estela, V. Cerdà, M.A. Segundo, J.L.F.C. Li... more Please cite this article as: M. Manera, M. Miró, J.M. Estela, V. Cerdà, M.A. Segundo, J.L.F.C. Lima, Flow-through solid-phase reflectometric method for simultaneous multiresidue determination of nitrophenol derivatives, Analytica Chimica Acta (2007), Abstract In this paper, a flow-through optosensor based on diffuse reflectance spectroscopy and multivariate regression modelling is proposed for simultaneous multiresidue determination of trace level concentrations of nitro-substituted phenols. The optrode integrates on-line anion-exchange sorptive preconcentration and matrix removal with direct detection of sorbed species onto the sensing layer and chemometric deconvolution of overlapped spectra. After recording of the reflectometric spectrum, fast chemosensor regeneration is accomplished with an acidic methanolic eluent followed by a metered volume of alkaline solution. The full automation of the analytical procedure is ensured by flow-programming as executed via a software-controlled multisyringe pump and a set of multiposition and solenoid valves.

Talanta, 2004

A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line... more A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on the MWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D. < 2.41%) and determination frequency of 12 h −1 were obtained.

International Journal of Environmental Analytical Chemistry, 2005

Considering the importance of monitoring the levels of nutrients present in soils and their avail... more Considering the importance of monitoring the levels of nutrients present in soils and their availability to plants, an automatic methodology is proposed based on multi-syringe flow injection analysis (MSFIA) for the spectrophotometric determination of available ...

Talanta, 2000

A sequential injection system for the spectrophotometric determination of reducing sugars in wine... more A sequential injection system for the spectrophotometric determination of reducing sugars in wines is described. The methodology is based on the formation of a coloured complex produced by the reaction of copper (I) with 2,9-dimethyl-1,10-phenanthroline (neocuproine), after reduction of copper (II) to copper (I) by reducing sugars. In the present SI system, a dialysis unit was incorporated not only to allow the sample dilution, but also to minimise the interference of some coloured compounds. In this way, direct sample introduction into the system was possible, without any previous treatment of the wine samples. The proposed method can be applied to the determination of reducing sugars in two concentration ranges: from 2 to 25 g l − 1 (table wines) and from 20 to 140 g l − 1 (Port wines). To perform determinations in these two ranges, the manifold configuration remained the same; just a few operational parameters were changed in the controlling software. A sampling-rate of 14 -18 samples per hour was obtained with good repeatability for ten consecutive injections of wine samples (relative standard deviations (RSD) B2.1%). The results obtained from 19 wine samples were comparable to those obtained by the reference method.

Analytica Chimica Acta, 2001

In the present work, a sequential injection system with spectrophotometric detection was develope... more In the present work, a sequential injection system with spectrophotometric detection was developed for the determination of free and total sulphur dioxide in wines. It was based on the formation of a coloured product from the reaction among SO 2 , formaldehyde and pararosaniline. A gas diffusion unit (GDU) was incorporated into the manifold to prevent the wine matrix interference in the spectrophotometric measurement. An acid solution was added to the sample prior to its passage through the donor channel of the GDU to promote gaseous SO 2 formation. For the free SO 2 determination, the sample was directly aspirated into the holding coil; for the total SO 2 determination, the sample was processed after previous in-line hydrolysis of bound SO 2 with an alkali solution.

Microchemical Journal, 2006

A multi-syringe flow injection system for the potentiometric determination of exchangeable potass... more A multi-syringe flow injection system for the potentiometric determination of exchangeable potassium in soil samples is proposed. Firstly, a manifold was devised to allow determination in soil extracts prepared off-line. It was possible to analyze samples ...

Analytica Chimica Acta, 2006

In the present work, an automatic method based on multi-syringe flow injection analysis (MSFIA) w... more In the present work, an automatic method based on multi-syringe flow injection analysis (MSFIA) was developed for the determination of total antioxidant capacity, measured as the cumulative capacity of the compounds present in the sample to scavenge free radicals, using the 2,2-diphenyl-1-picrylhydrazyl (DPPH • ) reaction. The determination is based on the colour disappearance due to the scavenging of DPPH • by antioxidant compounds monitored spectrophotometrically at 517 nm.

Analytica Chimica Acta, 2005

In multi-syringe flow injection analysis (MSFIA), devices as selection, injection or commutation ... more In multi-syringe flow injection analysis (MSFIA), devices as selection, injection or commutation valves must be incorporated to the manifold to provide access to sample and standard solutions. Therefore, the definition of sample amount can be either volume or time-based. In the present work, four configurations for sample introduction (two for each approach) were tested in order to establish if the different strategies affect the analytical signal in MSFIA systems. The mean absorbance value from ten consecutive injections of a bromothymol blue solution obtained for the time-based strategy was lower than that provided by the volume-based approach as the exact volume delivered by each configuration was different from the "theoretical" volume. For time-based configurations, the exact volume delivered is 2-5% lower than the theoretical value while for volume-based configurations, the volume delivered was between 6 and 46% larger than the theoretical volume. Moreover, for time-based sampling, the order of steps in the analytical cycle was of utmost importance since any alteration in the flow direction affected the volume delivered in the subsequent step in the analytical cycle. The influence of the two sampling approaches was also evaluated in the MSFIA systems for the spectrophotometric determination of phenolic compounds and the potentiometric determination of chloride. There was no evidence that the use of either volume or time-based sampling would improve the analytical features of these determinations when real samples were tested.

Journal of Agricultural and Food Chemistry, 2006

In the present work, an automatic flow procedure based on multi-syringe flow injection analysis w... more In the present work, an automatic flow procedure based on multi-syringe flow injection analysis was developed for the assessment of Folin-Ciocalteu reagent (FCR) reducing capacity in several types of food products using gallic acid as the standard. Different strategies for mixing of sample and reagent were tested (continuous flow of FCR, merging zones, and intercalated zones approaches); lower reagent consumption and higher determination throughput were attained for the merging zones approach (100 µL of sample + 100 µL of FCR). The application of the proposed method to compounds with known antioxidant activity (both phenolic and nonphenolic) and to samples (wines, beers, teas, soft drinks, and fruit juices) provided results similar to those obtained by the conventional batch method. The detection limit was 0.6 mg L -1 , and the determination frequency was about 12 h -1 . Good repeatability was attained (RSD < 1.3%, n ) 10).