Effect of the Ethanol/BTC Ratio on the Methane Uptake of Mechanochemically Synthesized MOF‐199
Chemistry – An Asian Journal, 2021
We report on a detailed textural analysis of mechanochemically synthesized MOF-199 including N 2 ... more We report on a detailed textural analysis of mechanochemically synthesized MOF-199 including N 2 adsorption-desorption and CO 2 adsorption isotherms data at 77 K and 273 K (up to atmospheric pressure), respectively, and CH 4 adsorption data at 298 K (up to 35 bar). We used the isotherm adsorption data to determine the micropore volume of the MOF-199 structures, to establish their methane uptake capacity and to understand how these properties depended on the Ethanol/BTC ratio used during the synthesis. The maximum methane uptake capacity for our specimens was recorded at 130 v/v at 35 bars. These results open an avenue for a better understanding of alternative manufacturing processes of MOF structures for gas storage applications.
Open-Source Portable Device for the Determination of Fluoride in Drinking Water
The prolonged exposure to fluorides results in the development of several diseases, from dental f... more The prolonged exposure to fluorides results in the development of several diseases, from dental fluorosis to crippling deformities of the spine and major joints. The population exposed to high fluoride concentration is located in developing countries where the assurance of water quality is difficult to perform. Addressing this challenge, an open-source system for the determination of fluoride in natural water was developed using the equilibrium between the red Fe-SCN complex and the colorless Fe-F. The reaction develops in cotton substrates to reduce the manipulation of liquid reagents and reduce the errors by nontrained operators. The system was optimized by image analysis and implemented in an open-source Arduino-based device and data was acquired through the serial port of a cell phone, which is also used as a power source, avoiding the use of a battery and reducing production costs. The device showed a detection limit of 0.7 mg L-1 and a linear range of up to 8 mg L-1. This extended detection limit makes the device useful for the application in regions where the fluoride concentration in drinking water is far higher than the United Nations limit (1.5 mg L-1), e.g., the United Republic of Tanzania, where the upper limit of F- was extended to 4 mg L-1 or in USA, where the Environmental Protection Agency established the Maximum Contaminant Level of F- in drinking water at 4 mg L-1. The method was tested with natural waters from the Arusha region in the northeast of Tanzania and validated against the results from ion chromatography showing a good correlation. The developed device exhibits chemical stability of 5 days, allowing it to be manufactured and distributed in local areas and, also, modified according to the requirements of the water composition due to Industry 4.0 concepts used in the design.
En el presente trabajo se han estudiado sistemas en flujo continuo para la valoracion de especies... more En el presente trabajo se han estudiado sistemas en flujo continuo para la valoracion de especies elementales de cromo, vanadio y metales del grupo IB (Cobre, Plata y Oro) mediante su aislamiento de la matriz y preconcentracion sobre sustratos ad-hoc sin utilizar la migracion diferencial de especies como alternativa analitica. [...]
Having access to safe drinking water is one of the 17 sustainable development goals defined by th... more Having access to safe drinking water is one of the 17 sustainable development goals defined by the United Nations (UN). However, many settlements around the globe have limited access to drinkable water due to non-anthropogenic pollution of the water sources. One of those pollutants is fluoride, which can induce major health problems. In this manuscript, we report on a post synthetic functionalization of metal organic frameworks for the sensing of fluoride in water. The proposed thermal condensation methodology allows for a high yield of functionalization using few steps, reducing reagent costs and generating minimal by-products. We identified a Rhodamine B functionalized Al-BDC-NH2 metal organic framework as one particularly suitable for fluoride detection in water.
The Long and Bright Path of a Lanthanide MOF: From Basics towards the Application
Chemistry – A European Journal, 2021
The development of portable, reliable, and low-cost sensors for assessing the quality of natural ... more The development of portable, reliable, and low-cost sensors for assessing the quality of natural water sources is of high relevance in developing countries as they can serve as an intermediate solution prior to the building of permanent potable water distribution infrastructure. These sensors should be simple to operate by non-trained operators and easy to manufacture locally. Lanthanide-based Metal-Organic Frameworks (MOFs) offer a trustable platform due to their intense emission in regions of the visible spectra and their high sensitivity to fluorides in water. We chose cotton as a substrate due to its high hydrophilicity, which together with the highly porous nature of the MOF, allows for shorter reaction times. The modified cotton was characterized by XRD, SEM as well as XAFS, hence probing the presence of [Tb(BTC)6(H2O)] (Tb-BTC) attachment to cotton. Changes in the emission when Tb-BTC modified cotton was exposed to water and aqueous fluoride solutions were monitored as a function of time. We identified crystalline phase changes that correlated to structural information. Finally, we used the Tb-BTC modified cotton to build a fluoride demonstrator sensor with a linear response up to 10ppm and 0.8ppm detection limit making it suitable for drinking water analysis under international regulations.
We report on a tunable solid-state approach to modify the acidity of cotton substrates using citr... more We report on a tunable solid-state approach to modify the acidity of cotton substrates using citric, oxalic, and fumaric acids. The first stage of the method involves soaking the cotton swatches in an ethanolic saturated solution of the corresponding acid. After drying, the carboxylation reaction proceeds at high temperature (T > 100 °C) and in solid state. We quantified the effect of temperature and reaction time on the solid-state carboxylation reaction, which allowed us to tune the carboxylation degree and the acidity of the surface. We characterized the modified cotton by performing adsorption isotherms and by determining the kinetics of adsorption of a cationic dye: methylene blue (MB). We found that the MB uptake kinetics varied as a function of the acidic strength of the surface, which is closely related to the strength of the acid used for surface modification. The proposed solid-state cotton carboxylation procedure allows us to achieve sustainable cotton modification, wh...
We report on the growing of metal-organic frameworks that are isoreticular and isostructural to U... more We report on the growing of metal-organic frameworks that are isoreticular and isostructural to UiO-66, onto cotton fabrics via a solvothermal method. Four different metal-organic frameworks (MOFs) (UiO-66, UiO-66-NH2, UiO-66-NDC, and UiO-67) were chosen as a case study. The presence of the UiO-based MOFs was confirmed through X-ray diffraction and Scanning Electron Microscopy. We used thermogravimetric analysis to quantify the amount of the MOF loading, which ranged from 0.8% to 2.6% m/m. We also explored the role of ligand size, growth time, and reaction temperature on the conformal coating of cotton fibers with these Zr-based MOFs. Cotton fabrics coated with Zr-based MOFs can find applications as selective filters in aggressive environments due to their enhanced chemical and thermal stabilities.
Zirconia-based materials are widely investigated and used as electrolytes in solid-oxide fuel cel... more Zirconia-based materials are widely investigated and used as electrolytes in solid-oxide fuel cells, oxygen sensors and electrochemical devices. These materials present polymorphism, which has a critical effect on their technologically important properties. The polymorphism is influenced by, among other factors, aliovalent dopant nature and content, grain size and interfacial energy. In this work, we investigated the crystal structure of ZrO 2-12 mol% CaO and −9 mol% Y 2 O 3 dense ceramics as a function of grain size. We found that the samples undergo a phase transition from the t form of the tetragonal phase to the cubic phase with an increase in grain size. This transition is directly detected by Raman spectroscopy and further evidence is given by a change in the activation energy for bulk ionic conduction. The transition occurs at an average grain size greater than 500 nm for both systems.
Fluoride Detection and Quantification, an Overview from Traditional to Innovative Material-Based Methods
Fluoride [Working Title]
Fluorine is the 13th most abundant element on Earth, and fluoride is part of our everyday lives, ... more Fluorine is the 13th most abundant element on Earth, and fluoride is part of our everyday lives, present in our drinking water, beauty products, and naturally present in food and beverages. It is a key element to increase the resistance of the dental enamel to the acidic bacteria attack and prevent dental decay. However, the ingestion of this anion for an extended period of time and in concentrations over the recommended limits can produce mild to severe health issues, called fluorosis, that can produce incorrect dental enamel formation, reduce the functionality of joints and even affect the bone structure. To avoid these terrible effects, it is necessary to control the fluoride levels in drinkable water, particularly in communities without access to safe water networks. To achieve this goal, the first step is to identify safe water sources and provision portable and reliable sensors to these communities. A major step towards safe water accessibility would be the implementation of t...
We report on the successful functionalization of cotton fabrics with a water-stable metal-organic... more We report on the successful functionalization of cotton fabrics with a water-stable metal-organic framework (MOF), UiO-66, under mild solvothermal conditions (80 °C) and its ability to adsorb and degrade water micropollutants. The functionalized cotton samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). UiO-66 crystals grew in a uniform and conformal manner over the surface of the cotton fibers. The cotton fabrics functionalized with UiO-66 frameworks exhibited an enhanced uptake capacity for methylchlorophenoxypropionic acid (MCPP), a commonly used herbicide. The functionalized fabrics also showed photocatalytic activity, demonstrated by the degradation of acetaminophen, a common pharmaceutical compound, under simulated sunlight irradiation. These results indicate that U...
Sólidos mesoporosos híbridos funcionalizados con N-(2-aminoetil)-3-aminopropilos como material ... more Sólidos mesoporosos híbridos funcionalizados con N-(2-aminoetil)-3-aminopropilos como material de sorción en SPE-FI-ETAAS: aplicación a la valoración de ultravestigios de plata.
Zr-based MOFs' light absorption spectra were shifted from UV to NIR via diazo coupling reacti... more Zr-based MOFs' light absorption spectra were shifted from UV to NIR via diazo coupling reaction. The photocatalytic performance of the solids was correlated with absorption edge.
A simple and sensitive HPLC post-derivatization method with colorimetric detection has been devel... more A simple and sensitive HPLC post-derivatization method with colorimetric detection has been developed for the determination of N-nitroso glyphosate in samples of technical glyphosate. Separation of the analyte was accomplished using an anionic exchange resin (2.50 mm × 4.00 mm i.d., 15 m particle size, functional group: quaternary ammonium salt) with Na 2 SO 4 0.0075 M (pH 11.5) (flow rate: 1.0 mL min −1) as mobile phase. After separation, the eluate was derivatized with a colorimetric reagent containing sulfanilamide 0.3% (w/v), [N-(1-naphtil)ethilendiamine] 0.03% (w/v) and HCl 4.5 M in a thermostatized bath at 95 • C. Detection was performed at 546 nm. All stages of the analytical procedure were optimized taking into account the concept of analytical minimalism: less operation times and costs; lower sample, reagents and energy consumption and minimal waste. The limit of detection (k = 3) calculated for 10 blank replicates was 0.04 mg L −1 (0.8 mg kg −1) in the solid sample which is lower than the maximum tolerable accepted by the Food and Agriculture Organization of the United Nations.
Spectrochimica Acta Part B: Atomic Spectroscopy, 2008
A flow injection hydride generation system with a metal furnace atomizer (Inconel 600® alloy) was... more A flow injection hydride generation system with a metal furnace atomizer (Inconel 600® alloy) was employed for Bi and Se determination. The presented methods have linear ranges up to 200 and 500 μg L − 1 for Bi and Se, respectively, with good linearities (r 2 = 0.9997 and 0.9974, respectively). The limits of quantification obtained according to IUPAC recommendations were 2.3 μg L − 1 for Bi and 6 μg L − 1 for Se, and the relative standard deviations (N = 6) based on Bi and Se analytical responses from real samples were 2.7% and 10%, respectively. Accuracy evaluations were based on certified materials such as SRM 361, SRM 363, and SRM 364 (steel alloys) for Bi, Mess-3 (marine sediment), SRM 397 (human hair), and Bio-Rad2-69042 (urine) for Se. Good agreements between the results were obtained at the 95% confidence level, according to the t-test.
In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V... more In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V) and V(IV) is presented. The method involves a solid phase extraction-flow injection system coupled to electrothermal atomic absorption spectrometry (SPE-FI-ETAAS). The system holds two microcolumns (MC) set in parallel and filled with lab-made mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APS) and mesoporous silica MCM-41, respectively. The pre-concentration of V(V) is performed by sorption onto the first MC (C1) filled with APS at pH 3, whilst that of V(IV) is performed by sorption onto the second column (C2) filled with mesoporous silica MCM-41 at pH 5. Aqueous samples containing both analytes are loaded and, after pre-concentration (pre-concentration factor PCF = 10, sorption flow rate = 1 mL min −1 , sorption time = 10 min), they are eluted in separate vessels with hydroxylammonium chloride (HC) 0.1 mol L −1 in HCl 0.5 mol L −1 (elution volume = 1 mL, elution flow rate = 0.5 mL min −1). Afterwards, both analytes are determined through ETAAS with graphite furnace. Under optimized conditions, the main analytical figures of merit for V(V) and V(IV) are, respectively: detection limits (3 s): 0.5 and 0.6 g L −1 , linear range: 2-100 g L −1 (both analytes), sensitivity: 0.015 and 0.013 g −1 L and sample throughput: 6 h −1 (both analytes). Recoveries of both species were assayed in different water samples. Validation was performed through certified reference materials for ultratraces of total vanadium in river water.
Effect of the Ethanol/BTC Ratio on the Methane Uptake of Mechanochemically Synthesized MOF‐199
Chemistry – An Asian Journal, 2021
We report on a detailed textural analysis of mechanochemically synthesized MOF-199 including N 2 ... more We report on a detailed textural analysis of mechanochemically synthesized MOF-199 including N 2 adsorption-desorption and CO 2 adsorption isotherms data at 77 K and 273 K (up to atmospheric pressure), respectively, and CH 4 adsorption data at 298 K (up to 35 bar). We used the isotherm adsorption data to determine the micropore volume of the MOF-199 structures, to establish their methane uptake capacity and to understand how these properties depended on the Ethanol/BTC ratio used during the synthesis. The maximum methane uptake capacity for our specimens was recorded at 130 v/v at 35 bars. These results open an avenue for a better understanding of alternative manufacturing processes of MOF structures for gas storage applications.
Open-Source Portable Device for the Determination of Fluoride in Drinking Water
The prolonged exposure to fluorides results in the development of several diseases, from dental f... more The prolonged exposure to fluorides results in the development of several diseases, from dental fluorosis to crippling deformities of the spine and major joints. The population exposed to high fluoride concentration is located in developing countries where the assurance of water quality is difficult to perform. Addressing this challenge, an open-source system for the determination of fluoride in natural water was developed using the equilibrium between the red Fe-SCN complex and the colorless Fe-F. The reaction develops in cotton substrates to reduce the manipulation of liquid reagents and reduce the errors by nontrained operators. The system was optimized by image analysis and implemented in an open-source Arduino-based device and data was acquired through the serial port of a cell phone, which is also used as a power source, avoiding the use of a battery and reducing production costs. The device showed a detection limit of 0.7 mg L-1 and a linear range of up to 8 mg L-1. This extended detection limit makes the device useful for the application in regions where the fluoride concentration in drinking water is far higher than the United Nations limit (1.5 mg L-1), e.g., the United Republic of Tanzania, where the upper limit of F- was extended to 4 mg L-1 or in USA, where the Environmental Protection Agency established the Maximum Contaminant Level of F- in drinking water at 4 mg L-1. The method was tested with natural waters from the Arusha region in the northeast of Tanzania and validated against the results from ion chromatography showing a good correlation. The developed device exhibits chemical stability of 5 days, allowing it to be manufactured and distributed in local areas and, also, modified according to the requirements of the water composition due to Industry 4.0 concepts used in the design.
En el presente trabajo se han estudiado sistemas en flujo continuo para la valoracion de especies... more En el presente trabajo se han estudiado sistemas en flujo continuo para la valoracion de especies elementales de cromo, vanadio y metales del grupo IB (Cobre, Plata y Oro) mediante su aislamiento de la matriz y preconcentracion sobre sustratos ad-hoc sin utilizar la migracion diferencial de especies como alternativa analitica. [...]
Having access to safe drinking water is one of the 17 sustainable development goals defined by th... more Having access to safe drinking water is one of the 17 sustainable development goals defined by the United Nations (UN). However, many settlements around the globe have limited access to drinkable water due to non-anthropogenic pollution of the water sources. One of those pollutants is fluoride, which can induce major health problems. In this manuscript, we report on a post synthetic functionalization of metal organic frameworks for the sensing of fluoride in water. The proposed thermal condensation methodology allows for a high yield of functionalization using few steps, reducing reagent costs and generating minimal by-products. We identified a Rhodamine B functionalized Al-BDC-NH2 metal organic framework as one particularly suitable for fluoride detection in water.
The Long and Bright Path of a Lanthanide MOF: From Basics towards the Application
Chemistry – A European Journal, 2021
The development of portable, reliable, and low-cost sensors for assessing the quality of natural ... more The development of portable, reliable, and low-cost sensors for assessing the quality of natural water sources is of high relevance in developing countries as they can serve as an intermediate solution prior to the building of permanent potable water distribution infrastructure. These sensors should be simple to operate by non-trained operators and easy to manufacture locally. Lanthanide-based Metal-Organic Frameworks (MOFs) offer a trustable platform due to their intense emission in regions of the visible spectra and their high sensitivity to fluorides in water. We chose cotton as a substrate due to its high hydrophilicity, which together with the highly porous nature of the MOF, allows for shorter reaction times. The modified cotton was characterized by XRD, SEM as well as XAFS, hence probing the presence of [Tb(BTC)6(H2O)] (Tb-BTC) attachment to cotton. Changes in the emission when Tb-BTC modified cotton was exposed to water and aqueous fluoride solutions were monitored as a function of time. We identified crystalline phase changes that correlated to structural information. Finally, we used the Tb-BTC modified cotton to build a fluoride demonstrator sensor with a linear response up to 10ppm and 0.8ppm detection limit making it suitable for drinking water analysis under international regulations.
We report on a tunable solid-state approach to modify the acidity of cotton substrates using citr... more We report on a tunable solid-state approach to modify the acidity of cotton substrates using citric, oxalic, and fumaric acids. The first stage of the method involves soaking the cotton swatches in an ethanolic saturated solution of the corresponding acid. After drying, the carboxylation reaction proceeds at high temperature (T > 100 °C) and in solid state. We quantified the effect of temperature and reaction time on the solid-state carboxylation reaction, which allowed us to tune the carboxylation degree and the acidity of the surface. We characterized the modified cotton by performing adsorption isotherms and by determining the kinetics of adsorption of a cationic dye: methylene blue (MB). We found that the MB uptake kinetics varied as a function of the acidic strength of the surface, which is closely related to the strength of the acid used for surface modification. The proposed solid-state cotton carboxylation procedure allows us to achieve sustainable cotton modification, wh...
We report on the growing of metal-organic frameworks that are isoreticular and isostructural to U... more We report on the growing of metal-organic frameworks that are isoreticular and isostructural to UiO-66, onto cotton fabrics via a solvothermal method. Four different metal-organic frameworks (MOFs) (UiO-66, UiO-66-NH2, UiO-66-NDC, and UiO-67) were chosen as a case study. The presence of the UiO-based MOFs was confirmed through X-ray diffraction and Scanning Electron Microscopy. We used thermogravimetric analysis to quantify the amount of the MOF loading, which ranged from 0.8% to 2.6% m/m. We also explored the role of ligand size, growth time, and reaction temperature on the conformal coating of cotton fibers with these Zr-based MOFs. Cotton fabrics coated with Zr-based MOFs can find applications as selective filters in aggressive environments due to their enhanced chemical and thermal stabilities.
Zirconia-based materials are widely investigated and used as electrolytes in solid-oxide fuel cel... more Zirconia-based materials are widely investigated and used as electrolytes in solid-oxide fuel cells, oxygen sensors and electrochemical devices. These materials present polymorphism, which has a critical effect on their technologically important properties. The polymorphism is influenced by, among other factors, aliovalent dopant nature and content, grain size and interfacial energy. In this work, we investigated the crystal structure of ZrO 2-12 mol% CaO and −9 mol% Y 2 O 3 dense ceramics as a function of grain size. We found that the samples undergo a phase transition from the t form of the tetragonal phase to the cubic phase with an increase in grain size. This transition is directly detected by Raman spectroscopy and further evidence is given by a change in the activation energy for bulk ionic conduction. The transition occurs at an average grain size greater than 500 nm for both systems.
Fluoride Detection and Quantification, an Overview from Traditional to Innovative Material-Based Methods
Fluoride [Working Title]
Fluorine is the 13th most abundant element on Earth, and fluoride is part of our everyday lives, ... more Fluorine is the 13th most abundant element on Earth, and fluoride is part of our everyday lives, present in our drinking water, beauty products, and naturally present in food and beverages. It is a key element to increase the resistance of the dental enamel to the acidic bacteria attack and prevent dental decay. However, the ingestion of this anion for an extended period of time and in concentrations over the recommended limits can produce mild to severe health issues, called fluorosis, that can produce incorrect dental enamel formation, reduce the functionality of joints and even affect the bone structure. To avoid these terrible effects, it is necessary to control the fluoride levels in drinkable water, particularly in communities without access to safe water networks. To achieve this goal, the first step is to identify safe water sources and provision portable and reliable sensors to these communities. A major step towards safe water accessibility would be the implementation of t...
We report on the successful functionalization of cotton fabrics with a water-stable metal-organic... more We report on the successful functionalization of cotton fabrics with a water-stable metal-organic framework (MOF), UiO-66, under mild solvothermal conditions (80 °C) and its ability to adsorb and degrade water micropollutants. The functionalized cotton samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). UiO-66 crystals grew in a uniform and conformal manner over the surface of the cotton fibers. The cotton fabrics functionalized with UiO-66 frameworks exhibited an enhanced uptake capacity for methylchlorophenoxypropionic acid (MCPP), a commonly used herbicide. The functionalized fabrics also showed photocatalytic activity, demonstrated by the degradation of acetaminophen, a common pharmaceutical compound, under simulated sunlight irradiation. These results indicate that U...
Sólidos mesoporosos híbridos funcionalizados con N-(2-aminoetil)-3-aminopropilos como material ... more Sólidos mesoporosos híbridos funcionalizados con N-(2-aminoetil)-3-aminopropilos como material de sorción en SPE-FI-ETAAS: aplicación a la valoración de ultravestigios de plata.
Zr-based MOFs' light absorption spectra were shifted from UV to NIR via diazo coupling reacti... more Zr-based MOFs' light absorption spectra were shifted from UV to NIR via diazo coupling reaction. The photocatalytic performance of the solids was correlated with absorption edge.
A simple and sensitive HPLC post-derivatization method with colorimetric detection has been devel... more A simple and sensitive HPLC post-derivatization method with colorimetric detection has been developed for the determination of N-nitroso glyphosate in samples of technical glyphosate. Separation of the analyte was accomplished using an anionic exchange resin (2.50 mm × 4.00 mm i.d., 15 m particle size, functional group: quaternary ammonium salt) with Na 2 SO 4 0.0075 M (pH 11.5) (flow rate: 1.0 mL min −1) as mobile phase. After separation, the eluate was derivatized with a colorimetric reagent containing sulfanilamide 0.3% (w/v), [N-(1-naphtil)ethilendiamine] 0.03% (w/v) and HCl 4.5 M in a thermostatized bath at 95 • C. Detection was performed at 546 nm. All stages of the analytical procedure were optimized taking into account the concept of analytical minimalism: less operation times and costs; lower sample, reagents and energy consumption and minimal waste. The limit of detection (k = 3) calculated for 10 blank replicates was 0.04 mg L −1 (0.8 mg kg −1) in the solid sample which is lower than the maximum tolerable accepted by the Food and Agriculture Organization of the United Nations.
Spectrochimica Acta Part B: Atomic Spectroscopy, 2008
A flow injection hydride generation system with a metal furnace atomizer (Inconel 600® alloy) was... more A flow injection hydride generation system with a metal furnace atomizer (Inconel 600® alloy) was employed for Bi and Se determination. The presented methods have linear ranges up to 200 and 500 μg L − 1 for Bi and Se, respectively, with good linearities (r 2 = 0.9997 and 0.9974, respectively). The limits of quantification obtained according to IUPAC recommendations were 2.3 μg L − 1 for Bi and 6 μg L − 1 for Se, and the relative standard deviations (N = 6) based on Bi and Se analytical responses from real samples were 2.7% and 10%, respectively. Accuracy evaluations were based on certified materials such as SRM 361, SRM 363, and SRM 364 (steel alloys) for Bi, Mess-3 (marine sediment), SRM 397 (human hair), and Bio-Rad2-69042 (urine) for Se. Good agreements between the results were obtained at the 95% confidence level, according to the t-test.
In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V... more In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V) and V(IV) is presented. The method involves a solid phase extraction-flow injection system coupled to electrothermal atomic absorption spectrometry (SPE-FI-ETAAS). The system holds two microcolumns (MC) set in parallel and filled with lab-made mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APS) and mesoporous silica MCM-41, respectively. The pre-concentration of V(V) is performed by sorption onto the first MC (C1) filled with APS at pH 3, whilst that of V(IV) is performed by sorption onto the second column (C2) filled with mesoporous silica MCM-41 at pH 5. Aqueous samples containing both analytes are loaded and, after pre-concentration (pre-concentration factor PCF = 10, sorption flow rate = 1 mL min −1 , sorption time = 10 min), they are eluted in separate vessels with hydroxylammonium chloride (HC) 0.1 mol L −1 in HCl 0.5 mol L −1 (elution volume = 1 mL, elution flow rate = 0.5 mL min −1). Afterwards, both analytes are determined through ETAAS with graphite furnace. Under optimized conditions, the main analytical figures of merit for V(V) and V(IV) are, respectively: detection limits (3 s): 0.5 and 0.6 g L −1 , linear range: 2-100 g L −1 (both analytes), sensitivity: 0.015 and 0.013 g −1 L and sample throughput: 6 h −1 (both analytes). Recoveries of both species were assayed in different water samples. Validation was performed through certified reference materials for ultratraces of total vanadium in river water.
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