Papers by Miguel De La Guardia
Journal of the Brazilian Chemical Society, 2004
Foi desenvolvido um método simples usando Infra-Vermelho com Transformada de Fourier (IRFT) para ... more Foi desenvolvido um método simples usando Infra-Vermelho com Transformada de Fourier (IRFT) para a determinação de Imidaclopride em formulações pesticidas. As amostram foram diluídas com CHCl 3 e os espectros de IRFT de amostras e padrões foram obtidos numa resolução nominal de 4 cm-1 , entre 4000 e 900 cm-1 , com acumulação de 25 espectros. A determinação de Imidaclopride foi feita medindo-se tanto a área do sinal obtido entre 1577 e 1567 cm-1 ou a altura do sinal a 1572 cm-1 , ambos com correção de linha base horizontal a 1900 cm-1. Os limites de detecção atingidos da ordem de 9 µg g-1 , foram apropriados para a determinação de Imidoclopride em formulações comercias disponíveis. Os resultados com IRFT forma estatisticamente comparáveis àqueles encontrados para Cromatografia Líquida de Alta Performance (HPLC). O procedimento desenvolvido reduz o consumo de solventes orgânicos por preparação de amostra, de 53 mL de CH 3 CN requeridos com HPLC para 2,5 mL de CHCl 3 , reduzindo o descarte gerado, e aumenta a freqüência de medidas de 10 para 60 amostras h-1 , quando comparado ao método de referência usando HPLC-UV. A simple method has been developed for Fourier Transform Infrared (FTIR) determination of Imidacloprid in pesticide formulations. Samples were diluted with CHCl 3 and the FTIR spectra of samples and standards were obtained at a nominal resolution of 4 cm-1 from 4000 to 900 cm-1 accumulating 25 scans. Imidacloprid determination was based on the measure of either peak area from 1577 to 1567 cm-1 or peak height at 1572 cm-1 , both corrected using a horizontal baseline defined at 1900 cm-1. The limits of detection achieved, of the order of 9 µg g-1 , were appropriate for the determination of Imidacloprid in commercially available formulations. FTIR results were statistically comparable to those found by High Performance Liquid Chromatography (HPLC). The procedure developed reduces organic solvent consumption, per sample preparation, from 53 mL CH 3 CN required for HPLC to 2.5 mL CHCl 3 , and reduces waste generation also increasing the sample measurement frequency from 10 h-1 to 60 h-1 as compared with the HPLC-UV reference method.
Analytical and bioanalytical chemistry, 2010
A partial least squares (PLS) regression model based on attenuated total reflectance-Fourier tran... more A partial least squares (PLS) regression model based on attenuated total reflectance-Fourier transform infrared spectra of heated olive oil samples has been developed for the determination of polymerized triacylglycerides (PTGs) generated during thermal treatment of oil. Three different approaches for selection of the spectral regions used to build the PLS model were tested and compared: (1) variable selection based on expert knowledge, (2) uninformative variable elimination PLS, and (3) interval PLS. Each of the three variable selection methods provided PLS models from heated olive oil samples with excellent performance for the prediction of PTGs in fried olive oils with comparable model statistics. However, besides a high coefficient of determination (R 2 of 0.991) and low calibration, validation, and prediction errors of 1.14%, 1.21%, and 1.40% w/w, respectively, variable selection based on expert knowledge gave additionally almost identical low calibration (−0.0017% w/w) and prediction (−0.0023% w/w) bias. Furthermore, it was verified that the determination of PTGs was not influenced by the type of foodstuff fried in the olive oil.
Analytica Chimica Acta, 2006
It has been developed a general strategy for the determination of pesticides in agrochemicals by ... more It has been developed a general strategy for the determination of pesticides in agrochemicals by Fourier transform near infrared (FT-NIR) spectroscopy. The methodology is based on previous extraction of the active principles through sonication with acetonitrile and direct determination by transmission measurements, using glass vials as measurement cells and univariate calibration at selected wavenumbers as a function of the pesticide to be analyzed. Chlorsulfuron, metamitron, iprodione, pirimicarb, procymidone and tricyclazole were used as test molecules and data obtained by FT-NIR for 20 samples containing one of these active principles compare well with those found by reference liquid chromatography (HPLC) procedures. In short, FT-NIR provides relative standard deviations between 0.04 and 0.7% and limit of detection values ranging from 0.004 to 0.17 mg g −1 with recovery values between 96.4 and 100.5%. On the other hand, FT-NIR offers a 10 times faster methodology than chromatography ones and an environmentally friendly alternative which reduces the reagent consumption to 1 mL acetonitrile per sample.
Analytica Chimica Acta, 1997
Liquid-liquid extraction (LLE), solid phase extraction (SPE) and microwave-assisted extraction ar... more Liquid-liquid extraction (LLE), solid phase extraction (SPE) and microwave-assisted extraction are evaluated for Fourier transform infrared (FTIR) spectrometric determination of oil and grease in polluted waters. A fast microwave-assisted quantitative procedure is ...
The liquid–liquid equilibria of the system H 3 PO 4 –KCl–H 2 O–TBP was studied experimentally in ... more The liquid–liquid equilibria of the system H 3 PO 4 –KCl–H 2 O–TBP was studied experimentally in the concentration range 0–6 mol/kg. The obtained data were modelled using the Pitzer equation for the aqueous phase and the Sergievskii–Dannus relationship for the organic phase. A fairly good agreement was observed between the model and the experimental data.
Talanta, 2014
Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to stud... more Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to study the dynamic metabolomic responses of biological systems under different physiological or pathological conditions. To obtain an integrated snapshot of the system, metabolomic methods in biomedicine typically analyze biofluids (e.g. plasma) that require clean-up before being injected into LC-MS systems. However, high resolution LC-MS is costly in terms of resources required for sample and data analysis and care must be taken to prevent chemical (e.g. ion suppression) or statistical artifacts. Because of that, the effect of sample preparation on the metabolomic profile during metabolomic method development is often overlooked. This work combines an Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) and a multivariate exploratory data analysis for a cost-effective qualitative evaluation of major changes in sample composition during sample preparation. ATR-FTIR and LC-time of flight mass spectrometry (TOFMS) data from the analysis of a set of plasma samples precipitated using acetonitrile, methanol and acetone performed in parallel were used as a model example. Biochemical information obtained from the analysis of the ATR-FTIR and LC-TOFMS data was thoroughly compared to evaluate the strengths and shortcomings of FTIR biospectroscopy for assessing sample preparation in metabolomics studies. Results obtained show the feasibility of ATR-FTIR for the evaluation of major trends in the plasma composition changes among different sample pretreatments, providing information in terms of e.g., amino acids, proteins, lipids and carbohydrates overall contents comparable to those found by LC-TOFMS.
Talanta, 2014
Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to stud... more Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to study the dynamic metabolomic responses of biological systems under different physiological or pathological conditions. To obtain an integrated snapshot of the system, metabolomic methods in biomedicine typically analyze biofluids (e.g. plasma) that require clean-up before being injected into LC-MS systems. However, high resolution LC-MS is costly in terms of resources required for sample and data analysis and care must be taken to prevent chemical (e.g. ion suppression) or statistical artifacts. Because of that, the effect of sample preparation on the metabolomic profile during metabolomic method development is often overlooked. This work combines an Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) and a multivariate exploratory data analysis for a cost-effective qualitative evaluation of major changes in sample composition during sample preparation. ATR-FTIR and LC-time of flight mass spectrometry (TOFMS) data from the analysis of a set of plasma samples precipitated using acetonitrile, methanol and acetone performed in parallel were used as a model example. Biochemical information obtained from the analysis of the ATR-FTIR and LC-TOFMS data was thoroughly compared to evaluate the strengths and shortcomings of FTIR biospectroscopy for assessing sample preparation in metabolomics studies. Results obtained show the feasibility of ATR-FTIR for the evaluation of major trends in the plasma composition changes among different sample pretreatments, providing information in terms of e.g., amino acids, proteins, lipids and carbohydrates overall contents comparable to those found by LC-TOFMS.
Analytica Chimica Acta, 2015
Analytica Chimica Acta, 2015
A¯ow system, based on multicommutation and binary sampling, has been developed for improving the ... more A¯ow system, based on multicommutation and binary sampling, has been developed for improving the automated spectrophotometric determination of carbaryl with p-aminophenol (PAP) in order to reduce the waste volume and to preserve the maximum analytical performance. The procedure, which was implemented employing a¯ow network obtained by nesting ®ve, three-way solenoid valves controlled by means of a 386 microcomputer equipped with an electronic interface running software written in QUICK BASIC 4.5, provides a limit of detection of 26 mg l À1 , comparable to that obtained using a conventional ow injection (FIA) manifold and lower than that found by sequential injection analysis (SIA), but generating a total waste volume per sample of 1.7 ml comparable to that found in SIA and 6 times lower than that obtained by conventional FIA. # 0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 3 -2 6 7 0 ( 9 9 ) 0 0 2 5 7 -3
Analytica Chimica Acta, 2015
A¯ow system, based on multicommutation and binary sampling, has been developed for improving the ... more A¯ow system, based on multicommutation and binary sampling, has been developed for improving the automated spectrophotometric determination of carbaryl with p-aminophenol (PAP) in order to reduce the waste volume and to preserve the maximum analytical performance. The procedure, which was implemented employing a¯ow network obtained by nesting ®ve, three-way solenoid valves controlled by means of a 386 microcomputer equipped with an electronic interface running software written in QUICK BASIC 4.5, provides a limit of detection of 26 mg l À1 , comparable to that obtained using a conventional ow injection (FIA) manifold and lower than that found by sequential injection analysis (SIA), but generating a total waste volume per sample of 1.7 ml comparable to that found in SIA and 6 times lower than that obtained by conventional FIA. # 0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 3 -2 6 7 0 ( 9 9 ) 0 0 2 5 7 -3
A¯ow system, based on multicommutation and binary sampling, has been developed for improving the ... more A¯ow system, based on multicommutation and binary sampling, has been developed for improving the automated spectrophotometric determination of carbaryl with p-aminophenol (PAP) in order to reduce the waste volume and to preserve the maximum analytical performance. The procedure, which was implemented employing a¯ow network obtained by nesting ®ve, three-way solenoid valves controlled by means of a 386 microcomputer equipped with an electronic interface running software written in QUICK BASIC 4.5, provides a limit of detection of 26 mg l À1 , comparable to that obtained using a conventional ow injection (FIA) manifold and lower than that found by sequential injection analysis (SIA), but generating a total waste volume per sample of 1.7 ml comparable to that found in SIA and 6 times lower than that obtained by conventional FIA. # 0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 3 -2 6 7 0 ( 9 9 ) 0 0 2 5 7 -3
Talanta, 2004
An on-line automated flow injection system with microwave-assisted sample digestion was used to p... more An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF +HCl +HNO 3 ) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 l). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 g ml −1 (which corresponds to an Fe 2 O 3 content of 0.46%) and an analytical throughput of 10 h −1 were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.
Talanta, 2004
An on-line automated flow injection system with microwave-assisted sample digestion was used to p... more An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF +HCl +HNO 3 ) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 l). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 g ml −1 (which corresponds to an Fe 2 O 3 content of 0.46%) and an analytical throughput of 10 h −1 were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.
Talanta, 2004
An on-line automated flow injection system with microwave-assisted sample digestion was used to p... more An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF +HCl +HNO 3 ) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 l). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 g ml −1 (which corresponds to an Fe 2 O 3 content of 0.46%) and an analytical throughput of 10 h −1 were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.
Talanta, 2004
An on-line automated flow injection system with microwave-assisted sample digestion was used to p... more An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF +HCl +HNO 3 ) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 l). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 g ml −1 (which corresponds to an Fe 2 O 3 content of 0.46%) and an analytical throughput of 10 h −1 were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.
Talanta
Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to stud... more Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to study the dynamic metabolomic responses of biological systems under different physiological or pathological conditions. To obtain an integrated snapshot of the system, metabolomic methods in biomedicine typically analyse biofluids (e.g. plasma) that require clean-up before injection into LC-MS systems. However, high resolution LC-MS is costly in terms of resources required for sample and data analysis and care must be taken to prevent chemical (e.g. ion suppression) or statistical artifacts. Because of that, the effect of sample preparation on the metabolomic profile during metabolomic method development is often overlooked. This work combines Attenuated Total Reflectance – Fourier transform infrared (ATR-FTIR) and multivariate exploratory data analysis for a cost-effective qualitative evaluation of major changes in sample composition during sample preparation. ATR-FTIR and LC-time of flight...
Química Nova, 2000
Recebido em 3/8/98; aceito em 16/4/99 ARSENIC SPECIATION -A REVIEW. This paper provides a review ... more Recebido em 3/8/98; aceito em 16/4/99 ARSENIC SPECIATION -A REVIEW. This paper provides a review on separation methods and analytical techniques for the determination of several species of organic and inorganic arsenic in different matrices. Arsenic is an element whose speciation is of particular interest due to the great variation of toxicity levels exhibited for its different chemical forms. Arsenic (III) and As (V) are the most toxic species while organic compounds such as arsenobetaine (AsB), produced by methylation of inorganics species (carcinogenics) are relatively less toxic, hence the great importance of arsenic speciation in the determination of the degree of contamination of an environmental or biological system.
Química Nova, 2000
Recebido em 3/8/98; aceito em 16/4/99 ARSENIC SPECIATION -A REVIEW. This paper provides a review ... more Recebido em 3/8/98; aceito em 16/4/99 ARSENIC SPECIATION -A REVIEW. This paper provides a review on separation methods and analytical techniques for the determination of several species of organic and inorganic arsenic in different matrices. Arsenic is an element whose speciation is of particular interest due to the great variation of toxicity levels exhibited for its different chemical forms. Arsenic (III) and As (V) are the most toxic species while organic compounds such as arsenobetaine (AsB), produced by methylation of inorganics species (carcinogenics) are relatively less toxic, hence the great importance of arsenic speciation in the determination of the degree of contamination of an environmental or biological system.
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Papers by Miguel De La Guardia