Maria Larrechi | Universitat Rovira i Virgili (original) (raw)

Papers by Maria Larrechi

Research paper thumbnail of Spectroscopic and quantitative analysis of spiroorthoester synthesis by two-dimensional correlation and multivariate curve resolution methods of NIR data

The Analyst, 2008

Non-urothelial neoplasms of the bladder account for less than 5% of all bladder tumors. Leiomyosa... more Non-urothelial neoplasms of the bladder account for less than 5% of all bladder tumors. Leiomyosarcoma is the most common malignant mesenchymal tumor that arises in the adult bladder. Leiomyosarcomas of the bladder are considered to be highly aggressive tumors. Most patients present at an advanced stage, with less than 30% of patients presenting with stage T1 disease. Surgical resection still remains the cornerstone of treatment with the status of the surgical margin being a strong predictor of the outcome. A 59-year-old man presented to our institution with urinary urgency, and cystoscopic examination revealed a huge submucosal mass on the lateral bladder wall. A radical cystoprostatectomy and ileal neobladder procedure was performed. The patient was diagnosed with a primary leiomyosarcoma of the bladder. After 1 year of follow-up, there has been no recurrence or metastasis.

Research paper thumbnail of Two-dimensional Fourier transform infrared correlation spectroscopy and evolving factor analysis in the study of cationic curing of DGEBA and γ-valerolactone mixtures

Journal of Polymer Science Part A: Polymer Chemistry, 2008

Generalized two-dimensional (2D) correlation spectroscopy and evolving factor analysis (EFA) have... more Generalized two-dimensional (2D) correlation spectroscopy and evolving factor analysis (EFA) have been applied to the study of cationic curing reaction of mixtures of diglycidyl ether of bisphenol A (DGEBA) and c-valerolactone (c-VL). The reaction has been monitored by Fourier transform infrared spectroscopy. The reaction periods in which a chemical change takes place are identified using EFA and then the sequence of changes are established by means of the interpretation of the synchronous and asynchronous spectra obtained with 2D correlation spectroscopy. By combining this information, in the curing process, four reactions have been detected: (1) DGEBA and c-VL reaction to obtain a spiroorthoester intermediate, (2) homopolymerization of DGEBA, (3) copolymerization of DGEBA with the spiroorthoester intermediate, and (4) homopolymerization of the spiroorthoester. V

Research paper thumbnail of Synthesis and study of the thermal crosslinking of bis( m -aminophenyl) methylphosphine oxide based benzoxazine

Journal of Polymer Science Part A: Polymer Chemistry, 2008

Bis(m-aminophenyl)methylphosphine oxide based benzoxazine (Bz-BAMPO) was obtained using a three-s... more Bis(m-aminophenyl)methylphosphine oxide based benzoxazine (Bz-BAMPO) was obtained using a three-step synthetic method from the aromatic diamine and 2-hydroxybenzaldehyde as starting materials. The structure and purity of the monomer was confirmed by elemental analysis, FTIR, 1 H NMR, 13 C NMR and 31 P NMR spectra. The curing kinetics of Bz-BAMPO was investigated by nonisothermal differential scanning calorimetry (DSC) at different heating rates and by FTIR spectroscopy. The isoconversional method was used to evaluate the dependence of the effective activation energy on the extent of conversion. The evolving factor analysis (EFA) method was applied to the spectroscopic FTIR data obtained in monitoring benzoxazine homopolymerizations. V

Research paper thumbnail of Spectroscopic and quantitative chemometric analysis of the epoxidised oil/amine system

Journal of Near Infrared Spectroscopy, 2010

The competitiveness between the oxirane functional group and the ester functional group present i... more The competitiveness between the oxirane functional group and the ester functional group present in a derivative epoxidised oil was studied by monitoring a model system which involved epoxidised oleic oil and aniline (1 : 1). The reaction was carried out under isothermal conditions at 95°C and monitored in situ by near infrared (NIR) spectroscopy. This system is taken as a model of the curing process in the manufacture of epoxy resins from triglycerides and diamines. Conventional spectroscopic analysis and generalised two-dimensional NIR correlation spectroscopy analysis have led to the conclusion that, even though the formation of secondary amines by ring-opening of the oxirane group as a consequence of the nucleophilic attack of the aniline is prior, the formation of amides as a consequence of the ester group reactivity is a competitive reaction. The presence of the two aforementioned reactions is also in accordance with the significant number of factors found when the spectra data matrix was analysed by evolving factor analysis. By applying multivariate curve resolution-alternating least squares to the NIR spectra obtained during the reaction, it has been possible to obtain the concentration and the spectra profiles of each chemical species involved in the reaction. The performance of the model was assessed by two parameters: alternating least squares lack of fit (lof = 1.67 %) and explained variance (R 2 = 99.68%). The recovered spectra of the generated products have the characteristic bands associated with the two postulated reactions.

Research paper thumbnail of Spectroscopic Evidence of the Mechanism Involved in the Cationic Diglycidyl Ether of Bisphenol A Curing with Rare Earth Metal Triflates

Applied Spectroscopy, 2010

The cross-linking of diglycidyl ether of bisphenol A (DGEBA) using three rare earth triflates as ... more The cross-linking of diglycidyl ether of bisphenol A (DGEBA) using three rare earth triflates as initiators (lanthanum, ytterbium, and scandium) was studied by in situ Fourier transform infrared (FT-IR) spectroscopy. Cationic ring opening of epoxides can proceed through two different mechanisms: activated monomer (AM) and active chain end (ACE). Using advanced chemometric methods such as perturbation-correlation moving-window two dimensional correlation spectroscopy (PCMW2D) and multivariate curve resolution–alternating least squares (MCR-ALS) it has been possible to obtain spectroscopic evidence of the two mechanisms. Traditionally, the demonstration of different mechanism pathways requires designing specific experiments. The novelty of the present study is to find, without a specific experimental design, spectroscopic evidence of the pathway of the polymerization process and to analyze the effect of these initiators, as well as the evolution of the species that takes part in the c...

Research paper thumbnail of A Methodology to Estimate Concentration Profiles from Two-Dimensional Covariance Spectroscopy Applied to Kinetic Data

Applied Spectroscopy, 2010

Two-dimensional (2D) covariance analyses applied to spectroscopy data obtained while monitoring c... more Two-dimensional (2D) covariance analyses applied to spectroscopy data obtained while monitoring chemical processes allow exploring the chemical reactions involved. Some slices of the sample–sample covariance map are an approach to the concentration profiles of the reactive species and we present a novel methodology to identify them. The method overcomes problems habitually referenced in the application of this technique and it is based on the selection of spectral zones with similar standard deviation of the variables and row centering the spectra data in each zone. The slices are identified according to the correlation coefficient value. The method is illustrated using simulated spectra data set representatives of two model reactions A → B and A → I → B. It has been applied to analyze the effect of rare earth metal triflate initiators in the cationic curing process of diglycidyl ether of bisphenol A with γ-valerolactone. The number of significant slices found is equal to the number...

Research paper thumbnail of MCR–ALS for sequential estimation of FTIR–ATR spectra to resolve a curing process using global phase angle convergence criterion

Analytica Chimica Acta, 2009

Research paper thumbnail of Chromium speciation using sequential injection analysis and multivariate curve resolution

Analytica Chimica Acta, 2006

In this paper we develop a suitable method for the speciation of chromium in tanning and environm... more In this paper we develop a suitable method for the speciation of chromium in tanning and environmental water samples. We use sequential injection analysis (SIA) with a diode array detector linked to chemometric tools such as multivariate curve resolutionalternating least squares (MCR-ALS) to determine Cr(III) and Cr(VI) species. Although Cr(III) is an absorbent species, its sensitivity is much lower than that of Cr(VI). To increase its sensitivity, therefore, it was complexed with EDTA. This method involves generating a pH gradient in the system reactor that converts dichromate into chromate in such a way that, when the sample reaches the detector, selective areas are observed and a data matrix is obtained. Applying MCR enables Cr(III) and Cr(VI) to be successfully determined simultaneously in tanning and environmental wastewater samples.

Research paper thumbnail of An analytical overview of processes for removing organic dyes from wastewater effluents

TrAC Trends in Analytical Chemistry, 2010

Organic dyes are used in a wide range of industrial applications (eg, textiles, food products, co... more Organic dyes are used in a wide range of industrial applications (eg, textiles, food products, cosmetics and pharmaceuticals), so they are frequently found in wastewaters and are increasingly becoming an environmental problem. This critical overview covers the most ...

Research paper thumbnail of Application de l'analyse multidimensionnelle des données a la reconnaissance des vins rouges de la Rioja

Research paper thumbnail of Comprehensive near infrared study of Jatropha oil esterification with ethanol for biodiesel production

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 6, 2016

This work presents a comprehensive near infrared study for in-line monitoring of the esterificati... more This work presents a comprehensive near infrared study for in-line monitoring of the esterification reaction of high acid oils, such as Jatropha curcas oil, using ethanol. Parallel reactions involved in the process were carried out to select a spectral region that characterizes the evolution of the esterification reaction. Using absorbance intensities at 5176cm(-1), the conversion and kinetic behaviors of the esterification reaction were estimated. This method was applied to evaluate the influence of temperature and catalyst concentration on the estimates of initial reaction rate and ester conversion as responses to a 2(2) factorial experimental design. Employment of an alcohol/oil ratio of 16:1, catalyst concentration of 1.5% w/w, and temperatures at 65°C or 75°C, made it possible to reduce the initial acidity from 18% to 1.3% w/w, which is suitable for transesterification of high free fatty acid oils for biodiesel production. Using the proposed analytical method in the esterificat...

Research paper thumbnail of Tierra 3. Canarias

Research paper thumbnail of Anal. Chim. Acta 225, 69-81 (1989)

Research paper thumbnail of MCR-ALS. Band boundaries of feasible solutions for multivariate curve resolution-alternating least squares solutions

NIR news, 2006

Soft modelling methods, such as the Multivariate Curve Resolution– Alternating Least Squares meth... more Soft modelling methods, such as the Multivariate Curve Resolution– Alternating Least Squares method (MCR–ALS), applied to bilinear spectroscopic data obtained from monitoring a chemical reaction can resolve concentration and spectra profiles of the reacting species with no need for a chemical model. The solutions obtained by MCR–ALS, are often not unique because of the rotational and intensity ambiguities present in factor analysis decompositions of bilinear data. Instead of unique solutions, a band of feasible solutions is provided, all of which fit the experimental data equally well. The amplitude of these bands can be drastically reduced when constraints, which are inherent to the chemical system being studied, are applied while the concentration and spectra profiles are being estimated. Furthermore, constraints related to selectivity in concentration or spectral regions and knowledge of local rank conditions often make it possible to obtain solutions which are nearly or completely unique. Unfortunately, this is not the most common situation when data matrices obtained from the spectroscopic monitoring of chemical reactions are analysed. Several studies have reported procedures for optimising the calculation of the band boundaries of feasible solutions for a variety of systems, including chromatographic coelution systems, reaction equilibrium systems, batch first order reaction systems and polymerisation reactions. Unlike these previous studies, which analysed single data matrices, the present paper calculates band boundaries of feasible solutions for the case in which several spectral data matrices, arranged in an augmented data matrix, are simultaneously analysed. The system studied is the curing reaction between phenyl glycidyl ether (PGE) and aniline. The augmented matrices strategy for solving the rank deficiency problems in the system involves simultaneously analysing a set of data matrices (forming an augmented data matrix) obtained by near infrared monitoring of the reaction starting from several initial molar ratios for the reagents. The algorithm used to calculate the band boundaries of feasible solutions was adapted so that the ambiguity of all the profiles obtained, when an augmented matrix is analysed, could be evaluated simultaneously. The effects that the number and type of data matrices in the simultaneous analysis have on the amplitude of band boundaries were also studied. The results and discussion shown in this summary are an excerpt from a previous article.

Research paper thumbnail of Computer-aided voltammetric method development employing a knowledge-based expert system

TrAC Trends in Analytical Chemistry, 1992

ABSTRACT

Research paper thumbnail of Analysing the Temperature Effect on the Competitiveness of the Amine Addition versus the Amidation Reaction in the Epoxidized Oil/Amine System by MCR-ALS of FTIR Data

International journal of analytical chemistry, 2011

The evaluation of the temperature effect on the competitiveness between the amine addition and th... more The evaluation of the temperature effect on the competitiveness between the amine addition and the amidation reaction in a model cure acid-catalysed reaction between the epoxidized methyl oleate (EMO), obtained from high oleic sunflower oil, and aniline is reported. The study was carried out analysing the kinetic profiles of the chemical species involved in the system, which were obtained applying multivariate curve resolution-alternating least squares (MCR-ALS) to the Fourier transform infrared spectra data obtained from the reaction monitoring at two different temperatures (60°C and 30°C). At both experimental temperatures, two mechanisms were postulated: non-autocatalytic and autocatalytic. The different behaviour was discussed considering not only the influence of the temperature on the amidation reaction kinetic, but also the presence of the homopolymerization of the EMO reagent.

Research paper thumbnail of Resolution of phenol, and its di-hydroxyderivative mixtures by excitation–emission fluorescence using MCR-ALSApplication to the quantitative monitoring of phenol photodegradation

Talanta, 2007

The photodegradation of phenol using TiO 2 as catalyst was studied and monitored by fluorescence ... more The photodegradation of phenol using TiO 2 as catalyst was studied and monitored by fluorescence excitation-emission matrix (EEM). Hydroquinone, catechol and resorcinol were the dihydroxyderivative intermediates although in lower concentrations than phenol. The data were analyzed using a three-way multivariate curve resolution alternating least squares method (MCR-ALS) and augmented matrices. The procedure was assessed using synthetic samples prepared with a {4,3} Simplex-lattice design that considered a representative range of analyte concentrations. The results were analyzed in terms of overall RMSEP for the overall data set. A detailed study was made of how the analytes behaved at each concentration level and how the concentration of the other species affected the process. The method was used to quantify phenol in photodegradation samples with an overall prediction error of 5.37%. The conversion values were fitted to pseudo first-order kinetics and the apparent rate constant was calculated to be −4.9 × 10 −4 ± 5.2 × 10 −5 min −1 .

Research paper thumbnail of Strategy for introducing NIR spectroscopy and multivariate calibration techniques in industry

TrAC Trends in Analytical Chemistry, 2003

Analytical methods based on near infrared spectroscopy (NIR) and multivariate calibration techniq... more Analytical methods based on near infrared spectroscopy (NIR) and multivariate calibration techniques have important characteristics for industrial applications because they are quick and can be used to make direct determinations and extract information from several parameters from one single measurement. They can also be used in on-line applications. However, they have not been used in industry as much as one might expect because the validity of the calibration model must be assured when the signal is transformed. There are chemometric techniques for tackling every problem, but there are no specific guidelines about which procedure to use. In this article, we describe a practical strategy for introducing these methods. We discuss the relative merits of the various univariate and multivariate control techniques and describe how they might be used. We also discuss the standardisation of the calibration models and describe how to obtain robust models at low experimental cost. Finally, we illustrate our strategy with a practical case study from the petrochemical industry.

Research paper thumbnail of PARAFAC and MCR-ALS applied to the quantitative monitoring of the photodegradation process of polycyclic aromatic hydrocarbons using three-dimensional excitation emission fluorescent spectraComparative results with HPLC

Talanta, 2007

Two methods were developed for the simultaneous quantitative monitoring of photodegradation proce... more Two methods were developed for the simultaneous quantitative monitoring of photodegradation process of dibenz[a,h]anthracene (DibA), benz[a]anthracene (BaA), benz[a]pyrene (BaP) and benz[k]fluorantene (BkF) using excitation-emission fluorescence spectroscopy. Parallel factor analysis (PARAFAC) and multivariate curve resolution-alternating least squares (MCR-ALS) were satisfactory applied to the data obtained during this process. The results achieved were statistically compared by means of the joint interval test of slope and intercept, with the data obtained using the reference methodology, high performance liquid chromatography (HPLC) method. There are not significant differences between the methodologies proposed and the standard one, and may be a good alternative to the traditional methods of analysis for monitoring the degradation of these pollutants.

Research paper thumbnail of UV–visible-DAD and 1H-NMR spectroscopy data fusion for studying the photodegradation process of azo-dyes using MCR-ALS

Talanta, 2013

The photodegradation process of three azo-dyes - Acid Orange 61, Acid Red 97 and Acid Brown 425 -... more The photodegradation process of three azo-dyes - Acid Orange 61, Acid Red 97 and Acid Brown 425 - was monitored simultaneously by ultraviolet-visible spectroscopy with diode array detector (UV-vis-DAD) and (1)H-nuclear magnetic resonance ((1)H-NMR). Multivariate curve resolution-alternating least squares (MCR-ALS) was applied to obtain the concentration and spectral profile of the chemical compounds involved in the process. The analysis of the H-NMR data suggests there are more intermediate compounds than those obtained with the UV-vis-DAD data. The fusion of UV-vis-DAD and the (1)H-NMR signal before the multivariate analysis provides better results than when only one of the two detector signals was used. It was concluded that three degradation products were present in the medium when the three azo-dyes had practically degraded. This study is the first application of UV-vis-DAD and (1)H-NMR spectroscopy data fusion in this field and illustrates its potential as a quick method for evaluating the evolution of the azo-dye photodegradation process.

Research paper thumbnail of Spectroscopic and quantitative analysis of spiroorthoester synthesis by two-dimensional correlation and multivariate curve resolution methods of NIR data

The Analyst, 2008

Non-urothelial neoplasms of the bladder account for less than 5% of all bladder tumors. Leiomyosa... more Non-urothelial neoplasms of the bladder account for less than 5% of all bladder tumors. Leiomyosarcoma is the most common malignant mesenchymal tumor that arises in the adult bladder. Leiomyosarcomas of the bladder are considered to be highly aggressive tumors. Most patients present at an advanced stage, with less than 30% of patients presenting with stage T1 disease. Surgical resection still remains the cornerstone of treatment with the status of the surgical margin being a strong predictor of the outcome. A 59-year-old man presented to our institution with urinary urgency, and cystoscopic examination revealed a huge submucosal mass on the lateral bladder wall. A radical cystoprostatectomy and ileal neobladder procedure was performed. The patient was diagnosed with a primary leiomyosarcoma of the bladder. After 1 year of follow-up, there has been no recurrence or metastasis.

Research paper thumbnail of Two-dimensional Fourier transform infrared correlation spectroscopy and evolving factor analysis in the study of cationic curing of DGEBA and γ-valerolactone mixtures

Journal of Polymer Science Part A: Polymer Chemistry, 2008

Generalized two-dimensional (2D) correlation spectroscopy and evolving factor analysis (EFA) have... more Generalized two-dimensional (2D) correlation spectroscopy and evolving factor analysis (EFA) have been applied to the study of cationic curing reaction of mixtures of diglycidyl ether of bisphenol A (DGEBA) and c-valerolactone (c-VL). The reaction has been monitored by Fourier transform infrared spectroscopy. The reaction periods in which a chemical change takes place are identified using EFA and then the sequence of changes are established by means of the interpretation of the synchronous and asynchronous spectra obtained with 2D correlation spectroscopy. By combining this information, in the curing process, four reactions have been detected: (1) DGEBA and c-VL reaction to obtain a spiroorthoester intermediate, (2) homopolymerization of DGEBA, (3) copolymerization of DGEBA with the spiroorthoester intermediate, and (4) homopolymerization of the spiroorthoester. V

Research paper thumbnail of Synthesis and study of the thermal crosslinking of bis( m -aminophenyl) methylphosphine oxide based benzoxazine

Journal of Polymer Science Part A: Polymer Chemistry, 2008

Bis(m-aminophenyl)methylphosphine oxide based benzoxazine (Bz-BAMPO) was obtained using a three-s... more Bis(m-aminophenyl)methylphosphine oxide based benzoxazine (Bz-BAMPO) was obtained using a three-step synthetic method from the aromatic diamine and 2-hydroxybenzaldehyde as starting materials. The structure and purity of the monomer was confirmed by elemental analysis, FTIR, 1 H NMR, 13 C NMR and 31 P NMR spectra. The curing kinetics of Bz-BAMPO was investigated by nonisothermal differential scanning calorimetry (DSC) at different heating rates and by FTIR spectroscopy. The isoconversional method was used to evaluate the dependence of the effective activation energy on the extent of conversion. The evolving factor analysis (EFA) method was applied to the spectroscopic FTIR data obtained in monitoring benzoxazine homopolymerizations. V

Research paper thumbnail of Spectroscopic and quantitative chemometric analysis of the epoxidised oil/amine system

Journal of Near Infrared Spectroscopy, 2010

The competitiveness between the oxirane functional group and the ester functional group present i... more The competitiveness between the oxirane functional group and the ester functional group present in a derivative epoxidised oil was studied by monitoring a model system which involved epoxidised oleic oil and aniline (1 : 1). The reaction was carried out under isothermal conditions at 95°C and monitored in situ by near infrared (NIR) spectroscopy. This system is taken as a model of the curing process in the manufacture of epoxy resins from triglycerides and diamines. Conventional spectroscopic analysis and generalised two-dimensional NIR correlation spectroscopy analysis have led to the conclusion that, even though the formation of secondary amines by ring-opening of the oxirane group as a consequence of the nucleophilic attack of the aniline is prior, the formation of amides as a consequence of the ester group reactivity is a competitive reaction. The presence of the two aforementioned reactions is also in accordance with the significant number of factors found when the spectra data matrix was analysed by evolving factor analysis. By applying multivariate curve resolution-alternating least squares to the NIR spectra obtained during the reaction, it has been possible to obtain the concentration and the spectra profiles of each chemical species involved in the reaction. The performance of the model was assessed by two parameters: alternating least squares lack of fit (lof = 1.67 %) and explained variance (R 2 = 99.68%). The recovered spectra of the generated products have the characteristic bands associated with the two postulated reactions.

Research paper thumbnail of Spectroscopic Evidence of the Mechanism Involved in the Cationic Diglycidyl Ether of Bisphenol A Curing with Rare Earth Metal Triflates

Applied Spectroscopy, 2010

The cross-linking of diglycidyl ether of bisphenol A (DGEBA) using three rare earth triflates as ... more The cross-linking of diglycidyl ether of bisphenol A (DGEBA) using three rare earth triflates as initiators (lanthanum, ytterbium, and scandium) was studied by in situ Fourier transform infrared (FT-IR) spectroscopy. Cationic ring opening of epoxides can proceed through two different mechanisms: activated monomer (AM) and active chain end (ACE). Using advanced chemometric methods such as perturbation-correlation moving-window two dimensional correlation spectroscopy (PCMW2D) and multivariate curve resolution–alternating least squares (MCR-ALS) it has been possible to obtain spectroscopic evidence of the two mechanisms. Traditionally, the demonstration of different mechanism pathways requires designing specific experiments. The novelty of the present study is to find, without a specific experimental design, spectroscopic evidence of the pathway of the polymerization process and to analyze the effect of these initiators, as well as the evolution of the species that takes part in the c...

Research paper thumbnail of A Methodology to Estimate Concentration Profiles from Two-Dimensional Covariance Spectroscopy Applied to Kinetic Data

Applied Spectroscopy, 2010

Two-dimensional (2D) covariance analyses applied to spectroscopy data obtained while monitoring c... more Two-dimensional (2D) covariance analyses applied to spectroscopy data obtained while monitoring chemical processes allow exploring the chemical reactions involved. Some slices of the sample–sample covariance map are an approach to the concentration profiles of the reactive species and we present a novel methodology to identify them. The method overcomes problems habitually referenced in the application of this technique and it is based on the selection of spectral zones with similar standard deviation of the variables and row centering the spectra data in each zone. The slices are identified according to the correlation coefficient value. The method is illustrated using simulated spectra data set representatives of two model reactions A → B and A → I → B. It has been applied to analyze the effect of rare earth metal triflate initiators in the cationic curing process of diglycidyl ether of bisphenol A with γ-valerolactone. The number of significant slices found is equal to the number...

Research paper thumbnail of MCR–ALS for sequential estimation of FTIR–ATR spectra to resolve a curing process using global phase angle convergence criterion

Analytica Chimica Acta, 2009

Research paper thumbnail of Chromium speciation using sequential injection analysis and multivariate curve resolution

Analytica Chimica Acta, 2006

In this paper we develop a suitable method for the speciation of chromium in tanning and environm... more In this paper we develop a suitable method for the speciation of chromium in tanning and environmental water samples. We use sequential injection analysis (SIA) with a diode array detector linked to chemometric tools such as multivariate curve resolutionalternating least squares (MCR-ALS) to determine Cr(III) and Cr(VI) species. Although Cr(III) is an absorbent species, its sensitivity is much lower than that of Cr(VI). To increase its sensitivity, therefore, it was complexed with EDTA. This method involves generating a pH gradient in the system reactor that converts dichromate into chromate in such a way that, when the sample reaches the detector, selective areas are observed and a data matrix is obtained. Applying MCR enables Cr(III) and Cr(VI) to be successfully determined simultaneously in tanning and environmental wastewater samples.

Research paper thumbnail of An analytical overview of processes for removing organic dyes from wastewater effluents

TrAC Trends in Analytical Chemistry, 2010

Organic dyes are used in a wide range of industrial applications (eg, textiles, food products, co... more Organic dyes are used in a wide range of industrial applications (eg, textiles, food products, cosmetics and pharmaceuticals), so they are frequently found in wastewaters and are increasingly becoming an environmental problem. This critical overview covers the most ...

Research paper thumbnail of Application de l'analyse multidimensionnelle des données a la reconnaissance des vins rouges de la Rioja

Research paper thumbnail of Comprehensive near infrared study of Jatropha oil esterification with ethanol for biodiesel production

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 6, 2016

This work presents a comprehensive near infrared study for in-line monitoring of the esterificati... more This work presents a comprehensive near infrared study for in-line monitoring of the esterification reaction of high acid oils, such as Jatropha curcas oil, using ethanol. Parallel reactions involved in the process were carried out to select a spectral region that characterizes the evolution of the esterification reaction. Using absorbance intensities at 5176cm(-1), the conversion and kinetic behaviors of the esterification reaction were estimated. This method was applied to evaluate the influence of temperature and catalyst concentration on the estimates of initial reaction rate and ester conversion as responses to a 2(2) factorial experimental design. Employment of an alcohol/oil ratio of 16:1, catalyst concentration of 1.5% w/w, and temperatures at 65°C or 75°C, made it possible to reduce the initial acidity from 18% to 1.3% w/w, which is suitable for transesterification of high free fatty acid oils for biodiesel production. Using the proposed analytical method in the esterificat...

Research paper thumbnail of Tierra 3. Canarias

Research paper thumbnail of Anal. Chim. Acta 225, 69-81 (1989)

Research paper thumbnail of MCR-ALS. Band boundaries of feasible solutions for multivariate curve resolution-alternating least squares solutions

NIR news, 2006

Soft modelling methods, such as the Multivariate Curve Resolution– Alternating Least Squares meth... more Soft modelling methods, such as the Multivariate Curve Resolution– Alternating Least Squares method (MCR–ALS), applied to bilinear spectroscopic data obtained from monitoring a chemical reaction can resolve concentration and spectra profiles of the reacting species with no need for a chemical model. The solutions obtained by MCR–ALS, are often not unique because of the rotational and intensity ambiguities present in factor analysis decompositions of bilinear data. Instead of unique solutions, a band of feasible solutions is provided, all of which fit the experimental data equally well. The amplitude of these bands can be drastically reduced when constraints, which are inherent to the chemical system being studied, are applied while the concentration and spectra profiles are being estimated. Furthermore, constraints related to selectivity in concentration or spectral regions and knowledge of local rank conditions often make it possible to obtain solutions which are nearly or completely unique. Unfortunately, this is not the most common situation when data matrices obtained from the spectroscopic monitoring of chemical reactions are analysed. Several studies have reported procedures for optimising the calculation of the band boundaries of feasible solutions for a variety of systems, including chromatographic coelution systems, reaction equilibrium systems, batch first order reaction systems and polymerisation reactions. Unlike these previous studies, which analysed single data matrices, the present paper calculates band boundaries of feasible solutions for the case in which several spectral data matrices, arranged in an augmented data matrix, are simultaneously analysed. The system studied is the curing reaction between phenyl glycidyl ether (PGE) and aniline. The augmented matrices strategy for solving the rank deficiency problems in the system involves simultaneously analysing a set of data matrices (forming an augmented data matrix) obtained by near infrared monitoring of the reaction starting from several initial molar ratios for the reagents. The algorithm used to calculate the band boundaries of feasible solutions was adapted so that the ambiguity of all the profiles obtained, when an augmented matrix is analysed, could be evaluated simultaneously. The effects that the number and type of data matrices in the simultaneous analysis have on the amplitude of band boundaries were also studied. The results and discussion shown in this summary are an excerpt from a previous article.

Research paper thumbnail of Computer-aided voltammetric method development employing a knowledge-based expert system

TrAC Trends in Analytical Chemistry, 1992

ABSTRACT

Research paper thumbnail of Analysing the Temperature Effect on the Competitiveness of the Amine Addition versus the Amidation Reaction in the Epoxidized Oil/Amine System by MCR-ALS of FTIR Data

International journal of analytical chemistry, 2011

The evaluation of the temperature effect on the competitiveness between the amine addition and th... more The evaluation of the temperature effect on the competitiveness between the amine addition and the amidation reaction in a model cure acid-catalysed reaction between the epoxidized methyl oleate (EMO), obtained from high oleic sunflower oil, and aniline is reported. The study was carried out analysing the kinetic profiles of the chemical species involved in the system, which were obtained applying multivariate curve resolution-alternating least squares (MCR-ALS) to the Fourier transform infrared spectra data obtained from the reaction monitoring at two different temperatures (60°C and 30°C). At both experimental temperatures, two mechanisms were postulated: non-autocatalytic and autocatalytic. The different behaviour was discussed considering not only the influence of the temperature on the amidation reaction kinetic, but also the presence of the homopolymerization of the EMO reagent.

Research paper thumbnail of Resolution of phenol, and its di-hydroxyderivative mixtures by excitation–emission fluorescence using MCR-ALSApplication to the quantitative monitoring of phenol photodegradation

Talanta, 2007

The photodegradation of phenol using TiO 2 as catalyst was studied and monitored by fluorescence ... more The photodegradation of phenol using TiO 2 as catalyst was studied and monitored by fluorescence excitation-emission matrix (EEM). Hydroquinone, catechol and resorcinol were the dihydroxyderivative intermediates although in lower concentrations than phenol. The data were analyzed using a three-way multivariate curve resolution alternating least squares method (MCR-ALS) and augmented matrices. The procedure was assessed using synthetic samples prepared with a {4,3} Simplex-lattice design that considered a representative range of analyte concentrations. The results were analyzed in terms of overall RMSEP for the overall data set. A detailed study was made of how the analytes behaved at each concentration level and how the concentration of the other species affected the process. The method was used to quantify phenol in photodegradation samples with an overall prediction error of 5.37%. The conversion values were fitted to pseudo first-order kinetics and the apparent rate constant was calculated to be −4.9 × 10 −4 ± 5.2 × 10 −5 min −1 .

Research paper thumbnail of Strategy for introducing NIR spectroscopy and multivariate calibration techniques in industry

TrAC Trends in Analytical Chemistry, 2003

Analytical methods based on near infrared spectroscopy (NIR) and multivariate calibration techniq... more Analytical methods based on near infrared spectroscopy (NIR) and multivariate calibration techniques have important characteristics for industrial applications because they are quick and can be used to make direct determinations and extract information from several parameters from one single measurement. They can also be used in on-line applications. However, they have not been used in industry as much as one might expect because the validity of the calibration model must be assured when the signal is transformed. There are chemometric techniques for tackling every problem, but there are no specific guidelines about which procedure to use. In this article, we describe a practical strategy for introducing these methods. We discuss the relative merits of the various univariate and multivariate control techniques and describe how they might be used. We also discuss the standardisation of the calibration models and describe how to obtain robust models at low experimental cost. Finally, we illustrate our strategy with a practical case study from the petrochemical industry.

Research paper thumbnail of PARAFAC and MCR-ALS applied to the quantitative monitoring of the photodegradation process of polycyclic aromatic hydrocarbons using three-dimensional excitation emission fluorescent spectraComparative results with HPLC

Talanta, 2007

Two methods were developed for the simultaneous quantitative monitoring of photodegradation proce... more Two methods were developed for the simultaneous quantitative monitoring of photodegradation process of dibenz[a,h]anthracene (DibA), benz[a]anthracene (BaA), benz[a]pyrene (BaP) and benz[k]fluorantene (BkF) using excitation-emission fluorescence spectroscopy. Parallel factor analysis (PARAFAC) and multivariate curve resolution-alternating least squares (MCR-ALS) were satisfactory applied to the data obtained during this process. The results achieved were statistically compared by means of the joint interval test of slope and intercept, with the data obtained using the reference methodology, high performance liquid chromatography (HPLC) method. There are not significant differences between the methodologies proposed and the standard one, and may be a good alternative to the traditional methods of analysis for monitoring the degradation of these pollutants.

Research paper thumbnail of UV–visible-DAD and 1H-NMR spectroscopy data fusion for studying the photodegradation process of azo-dyes using MCR-ALS

Talanta, 2013

The photodegradation process of three azo-dyes - Acid Orange 61, Acid Red 97 and Acid Brown 425 -... more The photodegradation process of three azo-dyes - Acid Orange 61, Acid Red 97 and Acid Brown 425 - was monitored simultaneously by ultraviolet-visible spectroscopy with diode array detector (UV-vis-DAD) and (1)H-nuclear magnetic resonance ((1)H-NMR). Multivariate curve resolution-alternating least squares (MCR-ALS) was applied to obtain the concentration and spectral profile of the chemical compounds involved in the process. The analysis of the H-NMR data suggests there are more intermediate compounds than those obtained with the UV-vis-DAD data. The fusion of UV-vis-DAD and the (1)H-NMR signal before the multivariate analysis provides better results than when only one of the two detector signals was used. It was concluded that three degradation products were present in the medium when the three azo-dyes had practically degraded. This study is the first application of UV-vis-DAD and (1)H-NMR spectroscopy data fusion in this field and illustrates its potential as a quick method for evaluating the evolution of the azo-dye photodegradation process.