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Determina??o de zinco em solo utilizando colorimetria
Fraige, Karina;Crespilho, Frank Nelson;Rezende, Maria Olímpia Oliveira;
Química Nova , 2007, DOI: 10.1590/S0100-40422007000300016
Abstract: in terms of soil fertility, zinc is a micronutrient that is very important in the culture of soy, maize, rice and coffee, because it is a structural and functional component of a great number of enzymes. therefore, diverse methods have been used to determine zinc in soil. in this work we use colorimetry as a methods of zinc determination in soil using two methodologies of sample digesting, h2so4/h2o2 and hno3/h2o2. in order to compare the results, atomic absorption spectrometry (aas) was used. results show that colorimetric methods can be used due to good sensitivity and reproducibility, since the zinc calibration curve showed good linearity. comparing colorimetric methods with aas we observed that the results were equivalent, as proven by the statistical values of the f and t of student tests. furthermore, both methods of soil digesting can be used, leading to a flexible methodology of low-cost for routine zinc analyses in soil.
Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determina??o de metais em meio aquoso
Crespilho, Frank Nelson;Rezende, Maria Olímpia Oliveira;
Química Nova , 2004, DOI: 10.1590/S0100-40422004000600022
Abstract: since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the ph, the scan rate, and the preparation of the electrodes itself. there are various methos of preparing the electrodes. the goal of this paper is to review some of them. the advantages of using electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.
Distribui??o de compostos organoclorados nas águas e sedimentos da bacia do rio Piracicaba/SP - Brasil
Del Grande, Marcelo;Rezende, Maria Olímpia Oliveira;Rocha, Odete;
Química Nova , 2003, DOI: 10.1590/S0100-40422003000500011
Abstract: the great utilization of synthetic and persistent xenobiotic cumulative compounds is the main causes of the deterioration of aquatic ecosystems. the one of objective of this work was the determination of the organochlorine levels in the piracicaba river basin, situated at the center of s?o paulo state. four pcbs congeners, pcp and hcb were determined by gc-ecd in two different matrices: water and sediments. the pattern of the compound distribution indicated a dominance of pcp, hcb and pcb-200. the results indicated contamination in the sampling points located in campinas, piracicaba, santa bárbara d'oeste and sumaré cities.
Influência do meio reacional no comportamento fotoquímico do inseticida paration etílico
Santos, Francismário Ferreira;Rezende, Maria Olímpia Oliveira;
Química Nova , 2002, DOI: 10.1590/S0100-40422002000100010
Abstract: the photodegradation of parathion in natural and dezionised waters was studied under irradiation at two different wavelengths: 280 nm and 313 nm. the influence of humic acids was evaluated. the results demonstrated that the degradation occurred only due to photochemical processes. the chemical hydrolysis and biological processes can be neglected in this case. the addition of humic acids did not increase the photodegradation rate in either water samples (natural or dezionised). in alkaline solutions the photodegradation rate was higher in dezionised water when compared to natural waters. the kinetic degradation in all experiments obeyed a first order reaction pattern.
Determina??o da concentra??o micelar crítica de ácidos húmicos por medidas de condutividade e espectroscopia
Moraes, Solange Leite de;Rezende, Maria Olímpia Oliveira;
Química Nova , 2004, DOI: 10.1590/S0100-40422004000500004
Abstract: the aim of this study was the determination of the critical micelle concentration (cmc) of the sodium dodecyl sulfate (sds) surfactant using spectroscopic and conductimetric determinations and to compare these methodologies in the determination of the cmc of different humic acids (ha). the cmc obtained by conductimetric determination was satisfactory. by spectroscopic determination two values of the cmc were obtained for ha. these values can be to due the intra and intermolecular interactions in the ha structure.
Influência do meio reacional no comportamento fotoquímico do inseticida paration etílico
Santos Francismário Ferreira,Rezende Maria Olímpia Oliveira
Química Nova , 2002,
Abstract: The photodegradation of parathion in natural and dezionised waters was studied under irradiation at two different wavelengths: 280 nm and 313 nm. The influence of humic acids was evaluated. The results demonstrated that the degradation occurred only due to photochemical processes. The chemical hydrolysis and biological processes can be neglected in this case. The addition of humic acids did not increase the photodegradation rate in either water samples (natural or dezionised). In alkaline solutions the photodegradation rate was higher in dezionised water when compared to natural waters. The kinetic degradation in all experiments obeyed a first order reaction pattern.
Distribui o de compostos organoclorados nas águas e sedimentos da bacia do rio Piracicaba/SP - Brasil
Del Grande Marcelo,Rezende Maria Olímpia Oliveira,Rocha Odete
Química Nova , 2003,
Abstract: The great utilization of synthetic and persistent xenobiotic cumulative compounds is the main causes of the deterioration of aquatic ecosystems. The one of objective of this work was the determination of the organochlorine levels in the Piracicaba river basin, situated at the center of S o Paulo state. Four PCBs congeners, PCP and HCB were determined by GC-ECD in two different matrices: water and sediments. The pattern of the compound distribution indicated a dominance of PCP, HCB and PCB-200. The results indicated contamination in the sampling points located in Campinas, Piracicaba, Santa Bárbara d'Oeste and Sumaré cities.
Eletrodos de pasta de carbono modificados com ácidos húmicos: estudo e determina o de metais em meio aquoso
Crespilho Frank Nelson,Rezende Maria Olímpia Oliveira
Química Nova , 2004,
Abstract: Since 1992, the carbon paste electrodes modified with humic acids have been used for studying the behavior of metals in aqueous solutions. Many parameters influence the performance of the electrodes, such as the humic acid ratio, the nature of the humic acid, the accumulation time, the pH, the scan rate, and the preparation of the electrodes itself. There are various methos of preparing the electrodes. The goal of this paper is to review some of them. The advantages of using electrodes modified with humic acids as electrochemical sensors for evaluating metals in aqueous solution are stressed.
Determina o da concentra o micelar crítica de ácidos húmicos por medidas de condutividade e espectroscopia
Moraes Solange Leite de,Rezende Maria Olímpia Oliveira
Química Nova , 2004,
Abstract: The aim of this study was the determination of the critical micelle concentration (CMC) of the sodium dodecyl sulfate (SDS) surfactant using spectroscopic and conductimetric determinations and to compare these methodologies in the determination of the CMC of different humic acids (HA). The CMC obtained by conductimetric determination was satisfactory. By spectroscopic determination two values of the CMC were obtained for HA. These values can be to due the intra and intermolecular interactions in the HA structure.
Avalia??o de solventes de extra??o por ultrassom usando-se cromatografia líquida de alta eficiência para a determina??o de hidrocarbonetos policíclicos aromáticos em solos contaminados
Cotta, Jussara Aparecida Oliveira;Rezende, Maria Olímpia Oliveira;Landgraf, Maria Diva;
Química Nova , 2009, DOI: 10.1590/S0100-40422009000800009
Abstract: a method using ultrasonication extraction for the determination of 17 polycyclic aromatic hydrocarbons (pahs), selected by the usepa and niosh as "consent decree" priority pollutants, in soil by high performance liquid chromatography (hplc) was studied. separation and detection were completed in 20 min with a c18 columm, acetonitrile-water gradient elution and ultraviolet absorption and fluorescence detections. the detection limits, for a 10 μl of solution injection, were less than 9,917 ng/g in uv detection and less than 1,866 ng/g in fluorescence detection. several organic solvents were tested for extraction of the 17 pahs from soils. acetone was the best solvent among the three solvents tested, and the order of the extraction efficiencies was: acetone>methanol>acetonitrile. ultrasonication using acetone as solvent extraction was used to evaluate the biodegradation of those compounds in contaminated soil during a vermicomposting process.
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