Eduardo Carasek | Universidade Federal de Santa Catarina - UFSC (Federal University of Santa Catarina) (original) (raw)

Papers by Eduardo Carasek

Chromatographia, 2004

This paper proposes use of solid-phase microextraction to monitor the gases resulting from therma... more This paper proposes use of solid-phase microextraction to monitor the gases resulting from thermal plasma pyrolysis, instead of the traditional process using an air-tight syringe. The results confirm that thermal plasma technology can be used to eliminate carbon tetrachloride, because dioxins and furans were not detected. Some chlorinated compounds, for example tetrachloroethylene, hexachloroethane, 1,1,2,3,4,4 hexachloro-1,3-butadiene, 1,2,3,4,5,5hexachloro-1,3-cyclopentadiene, and octachlorocyclopentadiene were detected, however. The results also confirm that this technique is more efficient than injection by means of an air-tight syringe for monitoring gases formed by the pyrolysis of carbon tetrachloride and enables detection of all viable sample constituents.

Journal of the Brazilian Chemical Society, 2005

O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com e... more O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com eletrodos de grafite e sistema de nebulização integrada para a eliminação de resíduos líquidos organoclorados (tetracloreto de carbono) em pequena escala. Os gases resultantes da pirólise do tetracloreto de carbono pelo plasma foram coletados e identificados por cromatografia gasosa acoplada ao espectrômetro de massa (GC-MS) e monitorados por cromatografia gasosa com detecção por ionização de chama (GC-FID). Observou-se que a tecnologia do plasma térmico elimina tetracloreto de carbono, caracterizando-se por baixo custo, simplicidade operacional e dimensões reduzidas, apresentando-se como uma alternativa ambientalmente correta, pois reduz a emissão total de gases organoclorados.

Talanta, 2005

The efficiency of niobium(V) oxide as a sorbent phase for solid phase microextraction (SPME) was ... more The efficiency of niobium(V) oxide as a sorbent phase for solid phase microextraction (SPME) was investigated. The thin glass-ceramic rod was coated with niobium(V) oxide using chemical vapor deposition and Nb 2 O 5 as a chemical precursor. Optimum conditions for the preparation and conditioning of the fibers are presented. The fibers were used for the extraction of a mixture of alcohols and a mixture of phenols from the headspace samples. The results obtained proved the suitability of niobium(V) oxide as a new SPME fiber. The calibration graphs for alcohols and phenols in a concentration range of 50-1000 g l −1 were linear (r > 0.995) and the detection limits were below 0.8 g l −1 level. The repeatability for one fiber (n = 6) under similar conditions was between 3 and 10.4%. The fiber-to-fiber reproducibility (n = 6) was between 5 and 15%.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005

Fiberglass with a composition of 29% Li2O, 1% ZrO2, 5% BaO, and 65% Si2O was coated with Nb2O5 us... more Fiberglass with a composition of 29% Li2O, 1% ZrO2, 5% BaO, and 65% Si2O was coated with Nb2O5 using the metallo-organic decomposition (MOD) technique. The morphology and coating homogeneity of the fibers was evaluated, using the scanning electron ...

Biological Trace Element Research, 2006

The quantification of target analytes in complex matrices requires special calibration approaches... more The quantification of target analytes in complex matrices requires special calibration approaches to compensate for additional capacity or activity in the matrix samples. The standard addition is one of the most important calibration procedures for quantification of analytes in such matrices. However, this technique requires a great number of reagents and material, and it consumes a considerable amount of time throughout the analysis. In this work, a new calibration procedure to analyze biological samples is proposed. The proposed calibration, called the addition calibration technique, was used for the determination of zinc (Zn) in blood serum and erythrocyte samples. The results obtained were compared with those obtained using conventional calibration techniques (standard addition and standard calibration). The proposed addition calibration was validated by recovery tests using blood samples spiked with Zn. The range of recovery for blood serum and erythrocyte samples were 90-132% and 76-112%, respectively. Statistical studies among results obtained by the addition technique and conventional techniques, using a paired two-tailed Student's t-test and linear regression, demonstrated good agreement among them.

Three different procedures for sample preparation have been compared for the determination of Cu,... more Three different procedures for sample preparation have been compared for the determination of Cu, Mo and Sb in airborne particulate matter (APM) collected on glass fiber filters using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). Direct solid sample analysis of the ground filters was compared with microwave-assisted acid leaching with aqua regia and ultrasound-assisted extraction also using aqua regia. The main absorption line at 324.754 nm or the secondary line at 216.509 nm was used for the determination of Cu, depending on the analyte content in the samples. The primary absorption line at 313.259 nm was used for Mo and the secondary line at 212.739 nm for Sb determination. The limits of detection (LOD, 3 ) found for the direct solid sampling method, based on ten atomizations of an unused filter were 15 g g −1 for all three analytes, corresponding to 40 ng m −3 for a typical air volume of 1440 m 3 collected over a period of 24 h. The LOD for the other two methods were less than a factor of two inferior, but the total time required for an analysis was significantly longer. The repeatability of the measurements was between 3 and 9% (n = 5), and the results obtained with the three methods did not show any significant difference. The ratio between the three analytes on the filters from areas of intense traffic was found to be around Cu:Mo:Sb ≈ 4:1:1.4, which suggests that the source of all three elements is brake linings, i.e., related to automobile traffic. When the ratio deviated significantly from the above values, the source of contamination was assumed to be of different origin.

Microchemical Journal, 2013

ABSTRACT This paper reports the preparation of fibers for solid phase microextraction by oxidized... more ABSTRACT This paper reports the preparation of fibers for solid phase microextraction by oxidized nitinol (NiTi) rods through contact with a boiling solution of H2O2. Also, a new optimization approach is described for the extraction of the volatile fraction of citrus juice based on the use of two extraction temperatures in the same HS-SPME procedure. A central composite design was performed by varying the extraction temperature from 5 to 50 °C and the extraction time from 20 to 80 min. The extracted compounds were divided into two groups (GR1 and GR2). Response surfaces were constructed, allowing the establishment of compromise conditions under which the temperatures could achieve a much better extraction and allow the identification of more volatile (GR1) and semi-volatile compounds (GR2). The optimized extraction conditions were obtained for a total extraction time of 40 min, comprising 24 min at 60 °C and 16 min at 5 °C.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2014

and sharing with colleagues.

Talanta, 2004

This study presents a new procedure for the determination of trace levels of copper(II) in an aqu... more This study presents a new procedure for the determination of trace levels of copper(II) in an aqueous matrix, through flow injection (FI) on-line preconcentration with a minicolumn packed with silica gel modified with 3(1-imidazolyl)propyl groups. After the preconcentration stage, the analyte was eluted with a HNO 3 solution and determined by flame atomic absorption spectrometry (FAAS). The measurements of the analytical signals were carried out as peak area and peak height with the objective of evaluating the most appropriate absorption measurement for the proposed method. Four procedures to calculate the experimental enrichment factor (EF) were also studied. For a preconcentration time of 90 s the enrichment factors found in this study varied between 19.5-25.8 and 36.2-42.2 for peak area and peak height, respectively. The precision of the proposed method was calculated for a solution containing 20 g l −1 of Cu(II), when 11.2 ml of solution was preconcentrated (n = 7), and their respective relative standard deviation (R.S.D.) values were 1.2 and 1.4% for peak area and peak height, respectively. The detection limits obtained were 0.4 and 0.2 g l −1 of Cu(II) for peak area and peak height, respectively, with a preconcentration time of 90 s. The on-line preconcentration system accuracy was evaluated through a recovery test on the aqueous samples and analysis of a certified material.

Talanta, 2013

and sharing with colleagues.

Talanta, 2006

An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythro... more An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythrocyte matrices by flame atomic absorption spectrometry (FAAS) was used. This procedure was based on adsorption of Zn(II) ions onto a minicolumn filled with silica gel, chemically modified with niobium(V) oxide (Nb 2 O 5 -SiO 2 ). The determination of the optimum conditions for Zn(II) preconcentration was done using two-level full factorial and Doehlert designs. In the optimization procedure, four variables (sample pH, eluent concentration, sample flow rate and eluent flow rate) were investigated. The results obtained from the full factorial design demonstrated that the sample pH and sample flow rate variables, and their interactions, were statistically significant. A Doehlert matrix was used in order to determine the optimum conditions for the sample pH and sample flow rate. The optimized conditions for sample pH and flow rate sampling were 6.6 and 7.1 ml min −1 , respectively, to obtain the maximum Zn(II) preconcentration and determination in the biological samples studied. Parameters of analytical curve, precision, effect of other ions in the proposed system and accuracy were achieved to assess the proposed method. The accuracy was confirmed by analysis of certified reference materials (urine Seronorm TM Trace Elements) and recovery tests in blood plasma and erythrocyte samples. Detection limit (3σ/S) of 0.77 g l −1 , precision (calculated as relative standard deviation) of 1.5% for Zn(II) concentration of 10 g l −1 (n = 7) and a sampling frequency of 27 samples/h were obtained from the proposed system.

Talanta, 2013

The aim of this work was to investigate the influence of magnesium acetylacetonate (MgA) on the s... more The aim of this work was to investigate the influence of magnesium acetylacetonate (MgA) on the signal of organic forms of vanadium in xylene solution by graphite furnace atomic absorption spectrometry. MgA alone or mixed with palladium acetylacetonate (PdA) was considered as a chemical modifier. It has been found that MgA does not improve, but decreases significantly the integrated absorbance of V in the form of alkyl-aryl sulfonates, acetylacetonates, porphyrins and in lubricating oils, while its effect is negligible in the case of ''dark products'' from petroleum distillation, i.e., heavy oil fractions and residues. The decrease is also observed in the presence of Pd. The MgA (or MgA þ PdA) effect on the integrated absorbance of V has been studied using the following variants: different ways of modifier application, various pyrolysis temperature, additional application of air ashing, preliminary pretreatment with iodine and methyltrioctylammonium chloride, application of various graphite furnace heating systems (longitudinal or transverse) and various optical and background correction systems (medium-resolution line source spectrometer with deuterium background correction or highresolution continuum source spectrometer). The experiments indicate formation of more refractory compounds as a possible reason for the decrease of the integrated absorbance for some forms of V in the presence of MgA. The application of MgA as a chemical modifier in V determination is not recommended. Results of this work have general importance as, apart from the intentional use of MgA as a modifier, organic Mg compounds, present in petroleum products for other reason (e.g. as an additive), can influence the signal of V compounds and hence the accuracy in V determination. Generally, petroleum products with known amount of V are recommended as standards; however, lubricating oils can be inadequate for ''dark products'' from petroleum distillation. In the case of unknown samples it is recommended to check the effect of Mg using recovery tests of V in a form that is affected by MgA.

Microchimica Acta, 2006

The efficiency of a glass-ceramic rod as a base for the preparation of SPME fibers using thermal ... more The efficiency of a glass-ceramic rod as a base for the preparation of SPME fibers using thermal immobilization was investigated. Glass-ceramic and fused silica rods were thermally immobilized with poly(butylacrylate) and their absorption capacity was compared. The absorption capacity between the fiber obtained for thermal immobilization of poly(butylacrylate) on glass-ceramic surface and commercially PA fiber was also compared. In this study the target analytes were phthalate esters and phenols. The results obtained for extraction of phenols from aqueous solutions using the headspace mode demonstrated the superiority of glass-ceramic in relation the silica gel rod as a base for SPME fiber. The direct SPME extraction of phthalate esters from aqueous solutions using commercial PA fiber and that obtained for thermal immobilization of poly(butylacrylate) on glass-ceramic rod presented similar results. The repeatability and the reproducibility among extractions using fibers developed in our laboratory were achieved.

Microchimica Acta, 2004

A comparative study of commercial C 18 chemically immobilized on silica and homemade C 18 , as so... more A comparative study of commercial C 18 chemically immobilized on silica and homemade C 18 , as sorbents for Pb complexed with O,Odiethyl-dithiophosphate (DDTP) in a flow injection preconcentration system is reported. The homemade C 18 sorbent was obtained by sorption of poly(methyloctadecylsiloxane) (PMODS) on the silica support followed by immobilization using thermal treatment. The method follows the concept of green chemistry, since there are no toxic residues after synthesis. The complexed Pb was formed in 1.0 mol L À1 HCl medium and retained on the minicolumn filled with the sorbents. The elution was carried out using ethanol, and the richest 210 mL fraction was collected and analyzed by flame atomic absorption spectrometry. Chemical and flow variables were optimized for each sorbent. The results demonstrated that the performance of the proposed homemade C 18 sorbent for preconcentration of Pb complexed with DDTP is very similar to commercial C 18 chemically bonded on silica. By processing 25 mL, the enrichment factors were 129 and 125 for commercial C 18 and homemade C 18 , respectively. The limit of detection for commer-cial and homemade C 18 was 0.2 mg L À1 and 0.6 mg L À1 , respectively. The relative standard deviation (RSD) was lower than 1.2% for both sorbents for a Pb concentration of 100 mg L À1 . The method was also applied successfully to the analysis of water samples, and the accuracy was tested by recovery measurements on spiked samples and biological reference material.

Journal of The Brazilian Chemical Society, 2005

O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com e... more O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com eletrodos de grafite e sistema de nebulização integrada para a eliminação de resíduos líquidos organoclorados (tetracloreto de carbono) em pequena escala. Os gases resultantes da pirólise do tetracloreto de carbono pelo plasma foram coletados e identificados por cromatografia gasosa acoplada ao espectrômetro de massa (GC-MS) e monitorados por cromatografia gasosa com detecção por ionização de chama (GC-FID). Observou-se que a tecnologia do plasma térmico elimina tetracloreto de carbono, caracterizando-se por baixo custo, simplicidade operacional e dimensões reduzidas, apresentando-se como uma alternativa ambientalmente correta, pois reduz a emissão total de gases organoclorados.

Journal of Separation Science, 2008

Application of poly(dimethylsiloxane) fiber sol-gel coated onto NiTi alloy electrodeposited with ... more Application of poly(dimethylsiloxane) fiber sol-gel coated onto NiTi alloy electrodeposited with zirconium oxide for the determination of organochlorine pesticides in herbal infusions A PDMS fiber sol -gel coated onto an NiTi alloy previously electrodeposited with zirconium oxide (named NiTi -ZrO 2 -PDMS) was applied to the determination of organochlorine pesticides (OCPs) in infusions of peppermint (Mentha piperita L.), lemon grass (Cymbopogon citratus Stapf), chamomile (Matricaria recutita L.), lemon balm (Melissa officinalis L.), and anise seeds (Pimpinella anisum L.). Salting-out effect, extraction time, and extraction temperature were optimized firstly by means of a full-factorial design and then using a Doehlert matrix. No salt addition and 50 min of extraction at 708C were the optimum conditions. Satisfactory LODs in the range of 2 -17 ng/L, as well as good correlation coefficients (at least 0.9981) in the linear range studied, were obtained. Calibration was successfully applied using an infusion of M. recutita L. and recovery tests were performed to ensure the accuracy of the method, with values in the range of 77 -120%. Comparison of the NiTi -ZrO 2 -PDMS with commercially available PDMS fibers showed that the proposed fiber has an extraction efficiency comparable to that of PDMS 30 lm for the compounds evaluated, demonstrating its potential applicability.

Journal of Pharmaceutical and Biomedical Analysis, 2011

A fast and reliable method has been developed for the determination of total and soluble fluorine... more A fast and reliable method has been developed for the determination of total and soluble fluorine in toothpaste, important quality control parameters in dentifrices. The method is based on the molecular absorption of gallium mono-fluoride, GaF, using a commercially available high-resolution continuum source atomic absorption spectrometer. Transversely heated platform tubes with zirconium as permanent chemical modifier were used throughout. Before each sample injection, a palladium and zirconium modifier solution and a gallium reagent were deposited onto the graphite platform and thermally pretreated to transform them into their active forms. The samples were only diluted and introduced directly into the graphite tube together with additional gallium reagent. Under these conditions the fluoride was stable up to a pyrolysis temperature of 550 • C, and the optimum vaporization (molecule formation) temperature was 1550 • C. The GaF molecular absorption was measured at 211.248 nm, and the limits of detection and quantification were 5.2 pg and 17 pg, respectively, corresponding to a limit of quantification of about 30 g g −1 (ppm) F in the original toothpaste. The proposed method was used for the determination of total and soluble fluorine content in toothpaste samples from different manufactures. The samples contained different ionic fluoride species and sodium monofluorophosphate (MFP) with covalently bonded fluorine. The results for total fluorine were compared with those obtained with a modified conventional headspace gas chromatographic procedure. Accuracy and precision of the two procedures were comparable, but the proposed procedure was much less labor-intensive, and about five times faster than the latter one.

Journal of Essential Oil Research, 2009

Static headspace/SPME volatiles from flowers and roots of the two Polygala species were analyzed ... more Static headspace/SPME volatiles from flowers and roots of the two Polygala species were analyzed by GC/MS. Methyl salicylate (89.1% and 97.8%) was found as the main volatile constituent in both roots of the P. paniculata and P. cyparissias, respectively. However, in the flowers of the P. paniculata and P. cyparissias, bornyl acetate (26.0% and 19.2%) and 1,8-cineol (13.0% and 7.2%)

Journal of Chromatography A, 2010

This review outlines recent progress in the research on some new classes of sorbents for extracti... more This review outlines recent progress in the research on some new classes of sorbents for extraction and microextraction techniques. Carbon nanotubes are allotropes of carbon with cylindrical structure. They are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Some applications of carbon nanotubes are presented in a perspective view. Molecular imprinting has proved to be an effective technique for the creation of recognition sites on a polymer scaffold. By a mechanism of molecular recognition, the molecularly imprinted polymers are used as selective tools for the development of various analytical techniques such as liquid chromatography, capillary electrochromatography, solid-phase extraction (SPE), binding assays and biosensors. Sol-gel chemistry provides a convenient pathway to create advanced material systems that can be effectively utilized to solve the solid phase microextraction fiber technology problems. This review is mainly focused on recent advanced developments in the design, synthesis and application of sol-gel in preparation of coatings for the SPME fibers.

Chromatographia, 2004

This paper proposes use of solid-phase microextraction to monitor the gases resulting from therma... more This paper proposes use of solid-phase microextraction to monitor the gases resulting from thermal plasma pyrolysis, instead of the traditional process using an air-tight syringe. The results confirm that thermal plasma technology can be used to eliminate carbon tetrachloride, because dioxins and furans were not detected. Some chlorinated compounds, for example tetrachloroethylene, hexachloroethane, 1,1,2,3,4,4 hexachloro-1,3-butadiene, 1,2,3,4,5,5hexachloro-1,3-cyclopentadiene, and octachlorocyclopentadiene were detected, however. The results also confirm that this technique is more efficient than injection by means of an air-tight syringe for monitoring gases formed by the pyrolysis of carbon tetrachloride and enables detection of all viable sample constituents.

Journal of the Brazilian Chemical Society, 2005

O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com e... more O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com eletrodos de grafite e sistema de nebulização integrada para a eliminação de resíduos líquidos organoclorados (tetracloreto de carbono) em pequena escala. Os gases resultantes da pirólise do tetracloreto de carbono pelo plasma foram coletados e identificados por cromatografia gasosa acoplada ao espectrômetro de massa (GC-MS) e monitorados por cromatografia gasosa com detecção por ionização de chama (GC-FID). Observou-se que a tecnologia do plasma térmico elimina tetracloreto de carbono, caracterizando-se por baixo custo, simplicidade operacional e dimensões reduzidas, apresentando-se como uma alternativa ambientalmente correta, pois reduz a emissão total de gases organoclorados.

Talanta, 2005

The efficiency of niobium(V) oxide as a sorbent phase for solid phase microextraction (SPME) was ... more The efficiency of niobium(V) oxide as a sorbent phase for solid phase microextraction (SPME) was investigated. The thin glass-ceramic rod was coated with niobium(V) oxide using chemical vapor deposition and Nb 2 O 5 as a chemical precursor. Optimum conditions for the preparation and conditioning of the fibers are presented. The fibers were used for the extraction of a mixture of alcohols and a mixture of phenols from the headspace samples. The results obtained proved the suitability of niobium(V) oxide as a new SPME fiber. The calibration graphs for alcohols and phenols in a concentration range of 50-1000 g l −1 were linear (r > 0.995) and the detection limits were below 0.8 g l −1 level. The repeatability for one fiber (n = 6) under similar conditions was between 3 and 10.4%. The fiber-to-fiber reproducibility (n = 6) was between 5 and 15%.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005

Fiberglass with a composition of 29% Li2O, 1% ZrO2, 5% BaO, and 65% Si2O was coated with Nb2O5 us... more Fiberglass with a composition of 29% Li2O, 1% ZrO2, 5% BaO, and 65% Si2O was coated with Nb2O5 using the metallo-organic decomposition (MOD) technique. The morphology and coating homogeneity of the fibers was evaluated, using the scanning electron ...

Biological Trace Element Research, 2006

The quantification of target analytes in complex matrices requires special calibration approaches... more The quantification of target analytes in complex matrices requires special calibration approaches to compensate for additional capacity or activity in the matrix samples. The standard addition is one of the most important calibration procedures for quantification of analytes in such matrices. However, this technique requires a great number of reagents and material, and it consumes a considerable amount of time throughout the analysis. In this work, a new calibration procedure to analyze biological samples is proposed. The proposed calibration, called the addition calibration technique, was used for the determination of zinc (Zn) in blood serum and erythrocyte samples. The results obtained were compared with those obtained using conventional calibration techniques (standard addition and standard calibration). The proposed addition calibration was validated by recovery tests using blood samples spiked with Zn. The range of recovery for blood serum and erythrocyte samples were 90-132% and 76-112%, respectively. Statistical studies among results obtained by the addition technique and conventional techniques, using a paired two-tailed Student's t-test and linear regression, demonstrated good agreement among them.

Three different procedures for sample preparation have been compared for the determination of Cu,... more Three different procedures for sample preparation have been compared for the determination of Cu, Mo and Sb in airborne particulate matter (APM) collected on glass fiber filters using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). Direct solid sample analysis of the ground filters was compared with microwave-assisted acid leaching with aqua regia and ultrasound-assisted extraction also using aqua regia. The main absorption line at 324.754 nm or the secondary line at 216.509 nm was used for the determination of Cu, depending on the analyte content in the samples. The primary absorption line at 313.259 nm was used for Mo and the secondary line at 212.739 nm for Sb determination. The limits of detection (LOD, 3 ) found for the direct solid sampling method, based on ten atomizations of an unused filter were 15 g g −1 for all three analytes, corresponding to 40 ng m −3 for a typical air volume of 1440 m 3 collected over a period of 24 h. The LOD for the other two methods were less than a factor of two inferior, but the total time required for an analysis was significantly longer. The repeatability of the measurements was between 3 and 9% (n = 5), and the results obtained with the three methods did not show any significant difference. The ratio between the three analytes on the filters from areas of intense traffic was found to be around Cu:Mo:Sb ≈ 4:1:1.4, which suggests that the source of all three elements is brake linings, i.e., related to automobile traffic. When the ratio deviated significantly from the above values, the source of contamination was assumed to be of different origin.

Microchemical Journal, 2013

ABSTRACT This paper reports the preparation of fibers for solid phase microextraction by oxidized... more ABSTRACT This paper reports the preparation of fibers for solid phase microextraction by oxidized nitinol (NiTi) rods through contact with a boiling solution of H2O2. Also, a new optimization approach is described for the extraction of the volatile fraction of citrus juice based on the use of two extraction temperatures in the same HS-SPME procedure. A central composite design was performed by varying the extraction temperature from 5 to 50 °C and the extraction time from 20 to 80 min. The extracted compounds were divided into two groups (GR1 and GR2). Response surfaces were constructed, allowing the establishment of compromise conditions under which the temperatures could achieve a much better extraction and allow the identification of more volatile (GR1) and semi-volatile compounds (GR2). The optimized extraction conditions were obtained for a total extraction time of 40 min, comprising 24 min at 60 °C and 16 min at 5 °C.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2014

and sharing with colleagues.

Talanta, 2004

This study presents a new procedure for the determination of trace levels of copper(II) in an aqu... more This study presents a new procedure for the determination of trace levels of copper(II) in an aqueous matrix, through flow injection (FI) on-line preconcentration with a minicolumn packed with silica gel modified with 3(1-imidazolyl)propyl groups. After the preconcentration stage, the analyte was eluted with a HNO 3 solution and determined by flame atomic absorption spectrometry (FAAS). The measurements of the analytical signals were carried out as peak area and peak height with the objective of evaluating the most appropriate absorption measurement for the proposed method. Four procedures to calculate the experimental enrichment factor (EF) were also studied. For a preconcentration time of 90 s the enrichment factors found in this study varied between 19.5-25.8 and 36.2-42.2 for peak area and peak height, respectively. The precision of the proposed method was calculated for a solution containing 20 g l −1 of Cu(II), when 11.2 ml of solution was preconcentrated (n = 7), and their respective relative standard deviation (R.S.D.) values were 1.2 and 1.4% for peak area and peak height, respectively. The detection limits obtained were 0.4 and 0.2 g l −1 of Cu(II) for peak area and peak height, respectively, with a preconcentration time of 90 s. The on-line preconcentration system accuracy was evaluated through a recovery test on the aqueous samples and analysis of a certified material.

Talanta, 2013

and sharing with colleagues.

Talanta, 2006

An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythro... more An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythrocyte matrices by flame atomic absorption spectrometry (FAAS) was used. This procedure was based on adsorption of Zn(II) ions onto a minicolumn filled with silica gel, chemically modified with niobium(V) oxide (Nb 2 O 5 -SiO 2 ). The determination of the optimum conditions for Zn(II) preconcentration was done using two-level full factorial and Doehlert designs. In the optimization procedure, four variables (sample pH, eluent concentration, sample flow rate and eluent flow rate) were investigated. The results obtained from the full factorial design demonstrated that the sample pH and sample flow rate variables, and their interactions, were statistically significant. A Doehlert matrix was used in order to determine the optimum conditions for the sample pH and sample flow rate. The optimized conditions for sample pH and flow rate sampling were 6.6 and 7.1 ml min −1 , respectively, to obtain the maximum Zn(II) preconcentration and determination in the biological samples studied. Parameters of analytical curve, precision, effect of other ions in the proposed system and accuracy were achieved to assess the proposed method. The accuracy was confirmed by analysis of certified reference materials (urine Seronorm TM Trace Elements) and recovery tests in blood plasma and erythrocyte samples. Detection limit (3σ/S) of 0.77 g l −1 , precision (calculated as relative standard deviation) of 1.5% for Zn(II) concentration of 10 g l −1 (n = 7) and a sampling frequency of 27 samples/h were obtained from the proposed system.

Talanta, 2013

The aim of this work was to investigate the influence of magnesium acetylacetonate (MgA) on the s... more The aim of this work was to investigate the influence of magnesium acetylacetonate (MgA) on the signal of organic forms of vanadium in xylene solution by graphite furnace atomic absorption spectrometry. MgA alone or mixed with palladium acetylacetonate (PdA) was considered as a chemical modifier. It has been found that MgA does not improve, but decreases significantly the integrated absorbance of V in the form of alkyl-aryl sulfonates, acetylacetonates, porphyrins and in lubricating oils, while its effect is negligible in the case of ''dark products'' from petroleum distillation, i.e., heavy oil fractions and residues. The decrease is also observed in the presence of Pd. The MgA (or MgA þ PdA) effect on the integrated absorbance of V has been studied using the following variants: different ways of modifier application, various pyrolysis temperature, additional application of air ashing, preliminary pretreatment with iodine and methyltrioctylammonium chloride, application of various graphite furnace heating systems (longitudinal or transverse) and various optical and background correction systems (medium-resolution line source spectrometer with deuterium background correction or highresolution continuum source spectrometer). The experiments indicate formation of more refractory compounds as a possible reason for the decrease of the integrated absorbance for some forms of V in the presence of MgA. The application of MgA as a chemical modifier in V determination is not recommended. Results of this work have general importance as, apart from the intentional use of MgA as a modifier, organic Mg compounds, present in petroleum products for other reason (e.g. as an additive), can influence the signal of V compounds and hence the accuracy in V determination. Generally, petroleum products with known amount of V are recommended as standards; however, lubricating oils can be inadequate for ''dark products'' from petroleum distillation. In the case of unknown samples it is recommended to check the effect of Mg using recovery tests of V in a form that is affected by MgA.

Microchimica Acta, 2006

The efficiency of a glass-ceramic rod as a base for the preparation of SPME fibers using thermal ... more The efficiency of a glass-ceramic rod as a base for the preparation of SPME fibers using thermal immobilization was investigated. Glass-ceramic and fused silica rods were thermally immobilized with poly(butylacrylate) and their absorption capacity was compared. The absorption capacity between the fiber obtained for thermal immobilization of poly(butylacrylate) on glass-ceramic surface and commercially PA fiber was also compared. In this study the target analytes were phthalate esters and phenols. The results obtained for extraction of phenols from aqueous solutions using the headspace mode demonstrated the superiority of glass-ceramic in relation the silica gel rod as a base for SPME fiber. The direct SPME extraction of phthalate esters from aqueous solutions using commercial PA fiber and that obtained for thermal immobilization of poly(butylacrylate) on glass-ceramic rod presented similar results. The repeatability and the reproducibility among extractions using fibers developed in our laboratory were achieved.

Microchimica Acta, 2004

A comparative study of commercial C 18 chemically immobilized on silica and homemade C 18 , as so... more A comparative study of commercial C 18 chemically immobilized on silica and homemade C 18 , as sorbents for Pb complexed with O,Odiethyl-dithiophosphate (DDTP) in a flow injection preconcentration system is reported. The homemade C 18 sorbent was obtained by sorption of poly(methyloctadecylsiloxane) (PMODS) on the silica support followed by immobilization using thermal treatment. The method follows the concept of green chemistry, since there are no toxic residues after synthesis. The complexed Pb was formed in 1.0 mol L À1 HCl medium and retained on the minicolumn filled with the sorbents. The elution was carried out using ethanol, and the richest 210 mL fraction was collected and analyzed by flame atomic absorption spectrometry. Chemical and flow variables were optimized for each sorbent. The results demonstrated that the performance of the proposed homemade C 18 sorbent for preconcentration of Pb complexed with DDTP is very similar to commercial C 18 chemically bonded on silica. By processing 25 mL, the enrichment factors were 129 and 125 for commercial C 18 and homemade C 18 , respectively. The limit of detection for commer-cial and homemade C 18 was 0.2 mg L À1 and 0.6 mg L À1 , respectively. The relative standard deviation (RSD) was lower than 1.2% for both sorbents for a Pb concentration of 100 mg L À1 . The method was also applied successfully to the analysis of water samples, and the accuracy was tested by recovery measurements on spiked samples and biological reference material.

Journal of The Brazilian Chemical Society, 2005

O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com e... more O presente trabalho consiste no desenvolvimento de uma tocha de plasma de corrente contínua com eletrodos de grafite e sistema de nebulização integrada para a eliminação de resíduos líquidos organoclorados (tetracloreto de carbono) em pequena escala. Os gases resultantes da pirólise do tetracloreto de carbono pelo plasma foram coletados e identificados por cromatografia gasosa acoplada ao espectrômetro de massa (GC-MS) e monitorados por cromatografia gasosa com detecção por ionização de chama (GC-FID). Observou-se que a tecnologia do plasma térmico elimina tetracloreto de carbono, caracterizando-se por baixo custo, simplicidade operacional e dimensões reduzidas, apresentando-se como uma alternativa ambientalmente correta, pois reduz a emissão total de gases organoclorados.

Journal of Separation Science, 2008

Application of poly(dimethylsiloxane) fiber sol-gel coated onto NiTi alloy electrodeposited with ... more Application of poly(dimethylsiloxane) fiber sol-gel coated onto NiTi alloy electrodeposited with zirconium oxide for the determination of organochlorine pesticides in herbal infusions A PDMS fiber sol -gel coated onto an NiTi alloy previously electrodeposited with zirconium oxide (named NiTi -ZrO 2 -PDMS) was applied to the determination of organochlorine pesticides (OCPs) in infusions of peppermint (Mentha piperita L.), lemon grass (Cymbopogon citratus Stapf), chamomile (Matricaria recutita L.), lemon balm (Melissa officinalis L.), and anise seeds (Pimpinella anisum L.). Salting-out effect, extraction time, and extraction temperature were optimized firstly by means of a full-factorial design and then using a Doehlert matrix. No salt addition and 50 min of extraction at 708C were the optimum conditions. Satisfactory LODs in the range of 2 -17 ng/L, as well as good correlation coefficients (at least 0.9981) in the linear range studied, were obtained. Calibration was successfully applied using an infusion of M. recutita L. and recovery tests were performed to ensure the accuracy of the method, with values in the range of 77 -120%. Comparison of the NiTi -ZrO 2 -PDMS with commercially available PDMS fibers showed that the proposed fiber has an extraction efficiency comparable to that of PDMS 30 lm for the compounds evaluated, demonstrating its potential applicability.

Journal of Pharmaceutical and Biomedical Analysis, 2011

A fast and reliable method has been developed for the determination of total and soluble fluorine... more A fast and reliable method has been developed for the determination of total and soluble fluorine in toothpaste, important quality control parameters in dentifrices. The method is based on the molecular absorption of gallium mono-fluoride, GaF, using a commercially available high-resolution continuum source atomic absorption spectrometer. Transversely heated platform tubes with zirconium as permanent chemical modifier were used throughout. Before each sample injection, a palladium and zirconium modifier solution and a gallium reagent were deposited onto the graphite platform and thermally pretreated to transform them into their active forms. The samples were only diluted and introduced directly into the graphite tube together with additional gallium reagent. Under these conditions the fluoride was stable up to a pyrolysis temperature of 550 • C, and the optimum vaporization (molecule formation) temperature was 1550 • C. The GaF molecular absorption was measured at 211.248 nm, and the limits of detection and quantification were 5.2 pg and 17 pg, respectively, corresponding to a limit of quantification of about 30 g g −1 (ppm) F in the original toothpaste. The proposed method was used for the determination of total and soluble fluorine content in toothpaste samples from different manufactures. The samples contained different ionic fluoride species and sodium monofluorophosphate (MFP) with covalently bonded fluorine. The results for total fluorine were compared with those obtained with a modified conventional headspace gas chromatographic procedure. Accuracy and precision of the two procedures were comparable, but the proposed procedure was much less labor-intensive, and about five times faster than the latter one.

Journal of Essential Oil Research, 2009

Static headspace/SPME volatiles from flowers and roots of the two Polygala species were analyzed ... more Static headspace/SPME volatiles from flowers and roots of the two Polygala species were analyzed by GC/MS. Methyl salicylate (89.1% and 97.8%) was found as the main volatile constituent in both roots of the P. paniculata and P. cyparissias, respectively. However, in the flowers of the P. paniculata and P. cyparissias, bornyl acetate (26.0% and 19.2%) and 1,8-cineol (13.0% and 7.2%)

Journal of Chromatography A, 2010

This review outlines recent progress in the research on some new classes of sorbents for extracti... more This review outlines recent progress in the research on some new classes of sorbents for extraction and microextraction techniques. Carbon nanotubes are allotropes of carbon with cylindrical structure. They are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Some applications of carbon nanotubes are presented in a perspective view. Molecular imprinting has proved to be an effective technique for the creation of recognition sites on a polymer scaffold. By a mechanism of molecular recognition, the molecularly imprinted polymers are used as selective tools for the development of various analytical techniques such as liquid chromatography, capillary electrochromatography, solid-phase extraction (SPE), binding assays and biosensors. Sol-gel chemistry provides a convenient pathway to create advanced material systems that can be effectively utilized to solve the solid phase microextraction fiber technology problems. This review is mainly focused on recent advanced developments in the design, synthesis and application of sol-gel in preparation of coatings for the SPME fibers.