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A new, versatile, and simple method for quantitative analysis of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry is described. These metals can be quantified by direct dissolution of fuel ethanol in water and subsequent voltammetric measurement after the accumulation step. A maximum limit of 20% ( v/ v) ethanol in water solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Chemical and operational optimum conditions were analyzed in this study; the values obtained were pH 2.9, a 4.7-microm thickness mercury film, a 1,000-rpm rotation frequency of the working electrode, and a 600-s pre-concentration time. Voltammetric measurements were obtained using linear scan (LSV), differential pulse (DPV), and square wave (SWV) modes and detection limits were in the range 10(-9)-10(-8) mol L(-1) for these metal species. The proposed method was compared with a traditional analytical technique, flame atomic absorption spectrometry (FAAS), for quantification of these metal species in commercial fuel ethanol samples.

The influence of sample preparation strategy of vegetables on the electrothermal behaviour of Se without and with chemical modifiers such as Pd(NO 3 ) 2 , Pd(NO 3 ) 2 + Mg(NO 3 ) 2 , Pd(NO 3 ) 2 + Cd(NO 3 ) 2 , pre-reduced Pd, Mg(NO 3 ) 2 , and Ni(NO 3 ) 2 was investigated. Acid digestates and slurries of vegetables (0.1% m/v in 1% v/v HNO 3 + 0.005% v/v of Triton X-100) were used to prepare reference solutions or slurries. For 10 μl of each modifier tested, pyrolysis and atomization temperatures were evaluated using pyrolysis and atomization curves, respectively. Best conditions, such as thermal stability, signal profile, repeatability and sensitivity were attained using Pd(NO 3 ) 2 as chemical modifier. The following heating program (temperature, ramp/hold time) of the graphite tube of the Varian SpectrAA-800Z atomic absorption spectrometer was used: dry step (85 °C, 5/0 s; 95 °C, 40/0 s; 120 °C, 10/5 s); pyrolysis step (1400 °C, 10/3s); atomization step (2200 °C, 1/2 s); clean step (2600 °C, 2/0 s). This pyrolysis temperature is 800 °C higher than when measuring without any modifier. For 20 μL sample volume and 10 μg Pd(NO 3 ) 2 , analytical curves in the 3.0–30 μg Se l −1 range were obtained. The method was applied for Se determination in acid digestates and slurries of 10 vegetable samples and one standard reference material (rice flower) and results were in agreement at 95% confidence level. Recoveries varied from 89 to 95% for spiked samples. The lifetime of the graphite tube was ca. 250 firings and the relative standard deviations ( n =12) for a typical acid digestate and slurry containing 20 μg Se l −1 were 3.8% and 8.3%, respectively. The limits of detection were 2.0 μg Se l −1 and 0.6 μg Se l −1 Se for digestates and slurries, respectively.

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l−1 HNO3 and in 1+1 v/v diluted wine using mixtures of Pd(NO3)2+Mg(NO3)2 and NH4H2PO4+Mg(NO3)2 as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l−1 HNO3, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l−1 Cd and 5.0–50 μg l−1 Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l−1 for Cd, 0.8 μg l−1 for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l−1 and for Pb at 500 μg l−1. The relative standard deviations (n=12) were typically

Este trabalho descreve uma revisão a respeito do uso do ligante dietilditiofosfato de amônio em química analítica e suas potencialidades no campo da análise química espectrofotométrica (UV/VIS) e espectrométrica (AAS, ICP-AES, ICP-MS) em diferentes matrizes e meios. A discriminação de espécies químicas por meio de complexações seletivas de elementos químicos com dietilditiofosfato e a hifenação de técnicas espectroscópicas a etapas de separação como extração em fase sólida, extração líquido-líquido, extração por "cloud point", são outros assuntos abordados neste trabalho.This paper describes a critical review on the use of ammonium diethyl dithiophosphate in analytical chemistry and the potentialities of this ligand in spectrophotometric (UV/VIS) and spectrometric (AAS, ICP-AES, ICP-MS) analyses in different matrices and medium. The speciation of chemical species by coupling complexation reactions between chemical elements and ammonium diethyl dithiophosphate as well as the hyphenation of spectroscopic techniques to separation steps such as solid phase extraction, solvent extraction, cloud point extraction, are also commented in this paper.

A new strategy for minimization of Cu 2+ and Pb 2+ interferences on the spectrophotometric determination of Cd 2+ by the Malachite green (MG)–iodide reaction using electrolytic deposition of interfering species and solid phase extraction of Cd 2+ in flow system is proposed. The electrolytic cell comprises two coiled Pt electrodes concentrically assembled. When the sample solution is electrolyzed in a mixed solution containing 5% (v/v) HNO 3 , 0.1% (v/v) H 2 SO 4 and 0.5 M NaCl, Cu 2+ is deposited as Cu on the cathode, Pb 2+ is deposited as PbO 2 on the anode while Cd 2+ is kept in solution. After electrolysis, the remaining solution passes through an AG1-X8 resin (chloride form) packed minicolumn in which Cd 2+ is extracted as CdCl 4 2− . Electrolyte compositions, flow rates, timing, applied current, and electrolysis time was investigated. With 60 s electrolysis time, 0.25 A applied current, Pb 2+ and Cu 2+ levels up to 50 and 250 mg l −1 , respectively, can be tolerated without interference. For 90 s resin loading time, a linear relationship between absorbance and analyte concentration in the 5.00–50.0 μg Cd l −1 range ( r 2 =0.9996) is obtained. A throughput of 20 samples per h is achieved, corresponding to about 0.7 mg MG and 500 mg KI and 5 ml sample consumed per determination. The detection limit is 0.23 μg Cd l −1 . The accuracy was checked for cadmium determination in standard reference materials, vegetables and tap water. Results were in agreement with certified values of standard reference materials and with those obtained by graphite furnace atomic absorption spectrometry at 95% confidence level. The R.S.D. for plant digests and water containing 13.0 μg Cd l −1 was 3.85% ( n =12). The recoveries of analyte spikes added to the water and vegetable samples ranged from 94 to 104%.

A spectrophotometric method for the determination of dipyrone in pharmaceutical preparations is proposed. This method is based on selective oxidation of dipyrone, in the presence of sulphuric acid, splitting off formaldehyde which reacts with chromotropic acid, also in a sulphuric acid medium, producing a violet–red compound (λmax 575 nm). Beer’s law is obeyed in a concentration range of 0.57–5.7 ppm dipyrone with an excellent correlation coefficient (r=0.9997). The results show a simple, accurate, selective and readily applied method to the determination of dipyrone in pharmaceutical products. The analytical results obtained for these products by the proposed method are in agreement with those of the Brazilian Pharmacopoeia procedure. No interference was observed from common excipients in formulations. Recoveries were within 98.7–101.2%, with standard deviations ranging from 0.2 to 1.7%.

This paper describes the construction of an electrode of the second kind, Pt |Hg|Hg2(Salic)2|Graphite, sensitive to salicylate. This electrode responds to the salicylate ion with a sensivity of 58.66 mV/decade over the range 6.0 〈10-4 ‐1.0〈10-1 mol/l at pH 6.0 and an ionic strength of 0.500 ‐3.00 mol/l, adjusted with NaClO4. The electrode is easily constructed, shows a fast response time, is low in cost, has excellent response stability, and has a lifetime greater than 18 months, which is much longer than those reported earlier for other systems. The influence of 10 different carboxylate and inorganic anions on the electrode response showed that there was negligible interference by most of these ions. It was used to determine aspirin in tablets (after hydrolysis of acetylsalicylic acid to salicylate) by means of the standard additions method. The results obtained using this electrode for aspirin determination, in three different samples of antithermic drugs, compared favorably with the results given by the British Pharmacopoeia method.

Amperometric titration using two Pt microelectrodes for the determination of phosphite in fertilizers based on the oxidation of analyte by iodine is proposed. The influence of pH, buffer composition, temperature, and foreign species on the end point and titration time was investigated. For titrations carried out at 70 degrees C using the pH 6.8 phosphate buffer, samples containing ca. 0.4% (m/v) P(2)O(5) could be titrated with 0.050 mol L(-1) iodine titrant, and the end point determined by extrapolating the linear portions of the plot to their intersection coincided with the end point identified by spectrophotometry. Accuracy was checked for phosphite determination in five fertilizer samples. Results were in agreement at the 95% confidence level (paired t test) with spectrophotometry. Recoveries of phosphite added to fertilizer samples ranged from 97% to 102% regardless of the amount of spiking in several determinations. The relative standard deviation (n = 10) was 1.0% for a diluted sample containing 0.050 mol L(-1) Na(2)HPO(3).

This paper describes the construction of an electrode of the second kind, Pt‖Hg‖Hg 2 (Bzt) 2 ‖graphite, sensitive to benzoate ion (Bzt). The electrode provides a near-Nernstian response (−58.19 mV/decade at 25°C) to benzoate ion in the concentration range 1.11 × 10 −1 to 5.00 × 10 −4 M at pH 7.0 and ionic strength 0.500–3.00M, adjusted with NaClO 4 . The electrode is easily constructed, shows a fast response time, is low in cost, has excellent response stability, and has a lifetime greater than 24 months, which is much longer than those earlier reported for other systems. A further salient feature of the electrode is that perchlorate does not interfere in its response, which may be advantageous in the analysis of perchloric acid-treated samples. It was applied to the determination of sodium benzoate in some commercial expectorating medicinal syrups using the standard additions method. The results obtained by the proposed procedure compare very favorably with those obtained through the reference method recommended by the United States Pharmacopeia.

Ethyl alcohol (ethanol) is considered to be a highly viable alternative fuel. Its production from biomass means that it can provide a source of energy that is both clean and renewable. The in‐ clusion of ethanol as a component of gasoline can help to reduce problems of pollution in many regions, since it eliminates the needto use tetraethyl lead (historically notorious as a highly tox‐ ic trace component of the atmosphere in major cities) as an anti-knock additive.

A method is described for the simultaneous determination of Cd, Cr, Ni and Pb in mineral water samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer (THGA) and a longitudinal Zeeman-effect background correction system. The electrothermal behavior of analytes during pyrolysis and atomization steps was studied without modifier, in presence of 5 mug Pd and 3 mug Mg(NO3)2 and in presence of 50 mug NH4H2PO4 and 3 mug Mg(NO3)2. A volume of 20 muL of a 0.028 mol L-1 HNO3 solution containing 50 mug L-1 Ni and Pb, 10 mug L-1 Cr and 5 mug L-1 Cd was dispensed into the graphite tube at 20 °C. The mixture palladium/magnesium was selected as the optimum modifier. The pyrolysis and atomization temperatures were fixed at 1000 °C and 2300 °C, respectively. The characteristic masses were calculated as 2.2 pg Cd, 10 pg Cr, 42 pg Ni and 66 pg Pb and the lifetime of the graphite tube was around 600 firings. Limits of detection based on integrated absorbance were 0.02 mug L-1 Cd, 0.94 mug L-1 Cr, 0.45 mug L-1 Ni and 0.75 mug L-1 Pb, which exceeded the requirements of Brazilian Food Regulation that establish the maximum permissible level for Cd, Cr, Ni and Pb at 3 mug L-1, 50 mug L-1, 20 mug L-1 and 10 mug L-1, respectively. The recoveries of Cd, Cr, Ni and Pb added to mineral water samples varied within the 93-108%, 96-104%, 87-101% and 98-108% ranges, respectively. Results of analysis of standard reference materials (National Institute of Standards and Technology: 1640-Trace Elements in Natural Water; 1643d-Trace Elements in Water) were in agreement with certified values at the 95% confidence level. Um método é descrito para a determinação simultânea de Cd, Cr, Ni e Pb em amostras de água mineral por espectrometria de absorção atômica em forno de grafite com um atomizador de grafite aquecido transversalmente (THGA) e um sistema de corretor de fundo por efeito Zeeman longitudinal. O comportamento eletrotérmico dos analitos durante as etapas de pirólise e atomização foi estudado sem modificador, na presença de 5 mig Pd e 3 mig Mg(NO3)2 e na presença de 50 mig NH4H2PO4 e 3 mig Mg(NO3)2. Um volume de 20 miL de uma solução 0,028 mol L-1 HNO3 contendo 50 mig L-1 Ni e Pb, 10 mig L-1 Cr e 5 mig L-1 Cd foi dispensado dentro do tubo de grafite a 20 °C. A mistura paládio/magnésio foi selecionada como o melhor modificador. As temperaturas de pirólise e atomização foram fixadas em 1000 °C e 2300 °C, respectivamente. As massas características calculadas foram 2,2 pg Cd, 10 pg Cr, 42 pg Ni e 66 pg Pb, e o tempo de vida do tubo de grafite foi cerca de 600 queimas. Os limites de detecção, baseados na absorbância integrada, foram 0,02 mig L-1 Cd, 0,94 mig L-1 Cr, 0,45 mig L-1 Ni e 0,75 mig L-1 Pb, que excederam os valores requeridos pela Legislação Brasileira, o qual estabelece um nível máximo permitido para Cd, Cr, Ni e Pb de 3 mig L-1, 50 mig L-1, 20 mig L-1 e 10 mig L-1, respectivamente. As recuperações de Cd, Cr, Ni e Pb adicionados a amostras de água mineral variaram dentro dos intervalos de 93-108%, 96-104%, 87-101% e 98-108%, respectivamente. Resultados de análises de materiais de referência padrão (National Institute of Standards and Technology: 1640-Trace Elements in Natural Water; 1643d-Trace Elements in Water) foram concordantes com seus valores certificados a um nível de confiança de 95%.

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer was used as a modifier for the direct determination of Se in soil extracts by graphite furnace atomic absorption spectrometry. Diethylenetriaminepentaacetic acid (0.0050 mol L(-1)) plus ammonium hydrogencarbonate (1.0 mol L(-1)) extracted predominantly available inorganic selenate from soil. The formation of a large amount of carbonaceous residue inside the atomizer was avoided with a first pyrolysis step at 600 degrees C assisted by air during 30 s. For 20 microL of soil extracts delivered to the atomizer and calibration by matrix matching, an analytical curve (10.0-100 microgram of L(-1)) with good linear correlation (r = 0.999) between integrated absorbance and analyte concentration was established. The characteristic mass was approximately 63 pg of Se, and the lifetime of the tube was approximately 750 firings. The limit of detection was 1.6 microgram L(-1), and the relative standard deviations (n = 12) were typically

A method for the direct determination of Pb in wines by simultaneous multi-element atomic absorption spectrometry (SIMAAS) using a transversely heated graphite atomizer, Zeeman-effect background corrector and internal standardization is proposed. Bismuth was used as an internal standard and Pd(NO3)2 plus Mg(NO3)2 as chemical modifier to stabilize both the analyte and the internal standard. The implementation of two pyrolysis steps avoided any build-up of carbonaceous residues on the graphite platform. All diluted samples (1 + 1 v/v) in 0.2% v/v HNO3 and reference solutions (5.0-50 microg l(-1) Pb in 0.2% v/v HNO3) were spiked with 25 microg l(-1) Bi. For a 20 microl aliquot dispensed into the graphite tube, a good correlation (r = 0.9997) was obtained between the ratio of the analyte signal to the internal standard signal and the analyte concentration of the reference solutions. The electrothermal behaviour of Pb and Bi in red, white and rosé wines were compared. In addition, absorbance variations due to changes in experimental conditions, such as atomizer temperature, integration time, injected sample volume, radiation beam intensity, graphite tube surface, dilution and sample composition, were minimized by using Bi as internal standard. Relative standard deviations of measurements based on integrated absorbance varied from 0.1 to 3.4% and from 0.5 to 7.3% (n = 12) with and without internal standard correction, respectively. Good recoveries (91-104%) for Pb spikes were obtained. The characteristic mass was 45 pg Pb and the limit of detection based on integrated absorbance was 0.9 microg l(-1) Pb. Internal standardization increased the lifetime of the tube by 25%. Direct determinations of Pb in wines with and without internal standardization approaches were in agreement at the 95% confidence level. The repeatability and the tube lifetime were improved when using Bi as internal standard. The improvement in accuracy using an internal standard was only observed when the analytical results were affected by errors.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:48:28Z No. of bitstreams: 1 S0100-40422001000600006.pdf: 477895 bytes, checksum: 20d3fa0dd5b1ee01c9a9d05d8c95d48f (MD5) Made available in DSpace on 2013-08-22T18:48:28Z (GMT). No. of bitstreams: 1 S0100-40422001000600006.pdf: 477895 bytes, checksum: 20d3fa0dd5b1ee01c9a9d05d8c95d48f (MD5) Previous issue date: 2001-12-01 Made available in DSpace on 2013-09-30T19:09:12Z (GMT). No. of bitstreams: 2 S0100-40422001000600006.pdf: 477895 bytes, checksum: 20d3fa0dd5b1ee01c9a9d05d8c95d48f (MD5) S0100-40422001000600006.pdf.txt: 27538 bytes, checksum: 471650b4d6b84f8fd9d40e670a5a99cf (MD5) Previous issue date: 2001-12-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:34Z No. of bitstreams: 2 S0100-40422001000600006.pdf: 477895 bytes, checksum: 20d3fa0dd5b1ee01c9a9d05d8c95d48f (MD5) S0100-40422001000600006.pdf.txt: 27538 bytes, checksum: 471650b4d6b84f8fd9d40e670a5a99cf (MD5) Made available in DSpace on 2014-05-20T14:19:34Z (GMT). No. of bitstreams: 2 S0100-40422001000600006.pdf: 477895 bytes, checksum: 20d3fa0dd5b1ee01c9a9d05d8c95d48f (MD5) S0100-40422001000600006.pdf.txt: 27538 bytes, checksum: 471650b4d6b84f8fd9d40e670a5a99cf (MD5) Previous issue date: 2001-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Simultaneous electrolytic deposition is proposed for minimization of Cu2+ and Pb2+ interferences on automated determination of Cd2+ by the Malachite Green-iodide reaction. During electrolysis of sample in a cell with two Pt electrodes and a medium adjusted to 5% (v/v) HNO3 + 0.1% (v/v) H2SO4 + 0.5 mol L-1 NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. With 60 s electrolysis time and 0.25 A current, Pb2+ and Cu2+ levels up to 50 and 250 mg L-1 respectively, can be tolerated without interference. With on-line extraction of Cd2+ in anionic resin minicolumn, calibration graph in the 5.00 - 50.0 µg Cd L-1 range is obtained, corresponding to twenty measurements per hour, 0.7 mg Malachite Green and 500 mg KI and 5 mL sample consumed per determination. Results of the determination of Cd in certified reference materials, vegetables and tap water were in agreement with certified values and with those obtained by GFAAS at 95% confidence level. The detection limit is 0.23 µg Cd L-1 and the RSD for typical samples containing 13.0 µg Cd L-1 was 3.85 % (n= 12). Universidade Estadual Paulista Instituto de Química Departamento de Química Analítica Universidade Estadual Paulista Instituto de Química Departamento de Química Analítica

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:09Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-01-01 Made available in DSpace on 2013-09-30T19:09:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:47Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:19:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Este trabalho descreve uma revisão a respeito do uso do ligante dietilditiofosfato de amônio em química analítica e suas potencialidades no campo da análise química espectrofotométrica (UV/VIS) e espectrométrica (AAS, ICP-AES, ICP-MS) em diferentes matrizes e meios. A discriminação de espécies químicas por meio de complexações seletivas de elementos químicos com dietilditiofosfato e a hifenação de técnicas espectroscópicas a etapas de separação como extração em fase sólida, extração líquido-líquido, extração por cloud point, são outros assuntos abordados neste trabalho. This paper describes a critical review on the use of ammonium diethyl dithiophosphate in analytical chemistry and the potentialities of this ligand in spectrophotometric (UV/VIS) and spectrometric (AAS, ICP-AES, ICP-MS) analyses in different matrices and medium. The speciation of chemical species by coupling complexation reactions between chemical elements and ammonium diethyl dithiophosphate as well as the hyphenation of spectroscopic techniques to separation steps such as solid phase extraction, solvent extraction, cloud point extraction, are also commented in this paper. Universidade Estadual Paulista Instituto de Química de Araraquara Departamento de Química Analítica Universidade Estadual Paulista Instituto de Química de Araraquara Departamento de Química Analítica

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:08Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-01-01 Made available in DSpace on 2013-09-30T19:09:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:47Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:19:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) A influência de digeridos e suspensões de açúcar no comportamento térmico de As usando Pd(NO3)2, Pd(NO3)2 + Mg(NO3)2, and Ni(NO3)2 como modificadores químicos foi investigada. Influência de 0,2%, 5%, 10% e 35% (v/v) HNO3 na calibração (1,00 - 10,0 µg As L-1) também foi feita. Um volume de 20 µL de amostra mais 5 µL Pd ou 5 µL Pd + 3 µL Mg, ou 20 µL Ni foi injetado no atomizador do GF AAS. Para cada modificador, temperaturas de pirólise e atomização foram avaliadas por meio de curvas de pirólise e de atomização, respectivamente. Para suspensão de açúcar, temperaturas de pirólise e atomização (Tp, Ta) obtidas foram: sem modificador (400° C, 2000° C); Pd (1400° C, 2200° C); Pd/Mg (1400° C, 2200° C) e Ni (1600° C, 2200° C). Os valores para digeridos de açúcar foram: sem modificador (400° C, 2200° C); Pd (1400° C, 2200° C); Pd/Mg (1400° C, 2200° C) e Ni (600° C, 2200° C). Paládio foi selecionado como o melhor modificador químico. O tempo de vida do tubo de grafte foi de aproximadamente 350 queimas, o RSD (n = 12) para uma amostra típica contendo 5,52 µg As L-1 foi < 2,2% e o limite de detecção foi 2,4 pg As. Recuperações entre 80 e 92% foram encontradas. The influence of digests and slurries of sugar on thermal behavior of As using Pd(NO3)2, Pd(NO3)2 + Mg(NO3)2, and Ni(NO3)2 as chemical modifiers was investigated. Influence of 0.2%, 5%, 10% and 35% (v/v) HNO3 on calibration (1.00 - 10.0 µg As L-1) was also done. A volume of 20 µL sample plus 5 µL Pd or 5 µL Pd + 3 µL Mg, or 20 µL Ni was injected into the atomizer of GF AAS. For each modifier, the pyrolysis and atomization temperatures were evaluated by means of pyrolysis and atomization curves, respectively. For sugar slurries, pyrolysis and atomization temperatures (Tp, Ta) found were: without modifier (400° C, 2000° C); Pd (1400° C, 2200° C); Pd/Mg (1400° C, 2200° C) and Ni (1600° C, 2200° C). The values for sugar digests were: without modifier (400° C, 2200° C); Pd (1400° C, 2200° C); Pd/Mg (1400° C, 2200° C) and Ni (600° C, 2200° C). Palladium was selected as the optimum chemical modifier. The lifetime of the graphite tube was ca. 350 firings, the RSD (n=12) for a typical 5.52 µg As L-1 sample was < 2.2% and the detection limit was 2.4 pg As. Recoveries between 80 and 92% of spiked samples were found. Universidade Estadual Paulista Instituto de Química de Araraquara Departamento de Química Analítica Universidade Estadual Paulista Instituto de Química de Araraquara Departamento de Química Analítica

Made available in DSpace on 2022-04-28T19:55:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-12-01 A flow injection system with online sample preparation is proposed for the determination of phosphite in liquid fertilizers by spectrophotometry. After loop-based injection, phosphite is oxidized by an acidic permanganate solution (1.0 10-2 mol L-1 KMnO4+1.0 mol L-1 H2SO4) in a heated reactor (50 °C). The phosphate generated is then determined by the molybdenum blue method. Influence of flow rates, temperature, and concentration and order of addition of reagents, sample volume, and reactor configuration for the blue complex formation on recorded signals were investigated. The flow system was applied to phosphite determination in commercial samples of liquid fertilizers. The proposed system handles about 80 samples per hour [0.05-0.40% (w/v) H3PO3; R = 0.9998], consuming about 80 μL sample, 1 mg KMnO4, 25 mg (NH4)6Mo7O24, and 10 mg ascorbic acid per determination. Results are precise [relative standard deviation ≤3.5% for 0.1% (w/v) H3PO3, n = 12] and in agreement with those obtained by gravimetry at 95% confidence level. Depto. de Quim. Analítica Instituto de Química Paulista-UNESP, P.O. Box 355, 14801-970, Araraquara, SP Depto. de Quim. Analítica Instituto de Química Paulista-UNESP, P.O. Box 355, 14801-970, Araraquara, SP

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:06Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-01-01 Made available in DSpace on 2013-09-30T19:39:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:21:03Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:21:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação para o Desenvolvimento da UNESP (FUNDUNESP) Este trabalho descreve a construção de um eletrodo de segunda espécie, Pt|Hg|Hg2Ox|Grafite, sensível ao íon oxalato (Ox). O eletrodo é construído facilmente, apresenta um rápido tempo de resposta, é de baixo custo, e tem um tempo de vida útil superior a 12 meses. O potencial molal padrão do eletrodo a 25ºC é 417,3 ± 1,0 mV. A validação do eletrodo foi conseguida pela determinação do produto de solubilidade,T K PS (I=0), do Hg2C2O4 (T K PS = (2,53 ± 0,21) x 10-13 mol². L-2). Uma característica favorável consiste no fato de que o eletrodo pode ser utilizado para determinar a concentração de íons oxalato livres em sistemas complexos de íons metálicos. This paper describes the construction of an electrode of the second kind, Pt|Hg|Hg2Ox|Grafite, sensitive to oxalate ion (Ox). The electrode is easily constructed, shows a fast response time, is low in cost, and has a lifetime greater than 12 months. The standard molal potential of the electrode at 25ºC is (417.3 ± 1,0) mV. The electrode validation has been carried out by determining the solubility product, T K PS (I=0), of Hg2C2O4 (T K PS = (2.53 ± 0.21) x 10-13 mol². L-2). A favorable feature lies in the fact that the electrode can be utilized to determine the concentration of free oxalate ions in complex systems of metallic ions. Universidade Estadual Paulista Instituto de Química Universidade Estadual Paulista Instituto de Química

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:08Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-01-01 Made available in DSpace on 2013-09-30T19:09:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:39Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:19:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Este trabalho descreve uma revisão a respeito do emprego da técnica de espectrometria de absorção atômica simultânea em forno de grafite (SIMAAS) em determinações multielementares de elementos-traço em diferentes matrizes. Os principais parâmetros envolvidos e que devem ser considerados em medidas multielementares, tais como, fonte de radiação, geometria do forno, programa de aquecimento e natureza e quantidade de modificador químico, são descritos. A review on the use of graphite furnace atomic absorption spectrometry for simultaneous multielement determination of metals at trace levels in different samples is described. The main parameters to be considered in multi-element analysis such as light sources, kind of graphite furnace tubes, time and temperature program, and composition and amount of modifier are summarized and discussed. Universidade Estadual Paulista Instituto de Química de Araraquara Departamento de Química Analítica Universidade Estadual Paulista Instituto de Química de Araraquara Departamento de Química Analítica

The molar single ion activity coefficient (yF) of fluoride ions was determined at 25 °C and ionic strengths between 0.100 and 3.00 mol L-1 NaClO4 using an ion-selective electrode. The activity coefficient dependency on ionic strength was determined to be ΦF = log yF = 0.2315I - 0.041I². The function ΦF(I), combined with functions obtained in previous work for copper (ΦCu) and hydrogen (ΦH), allowed us to make the estimation of the stoichiometric and thermodynamic protonation constants of some halides and pseudo-halides as well as the formation constants of some pseudo-halides and fluoride 1:1 bivalent cation complexes. The calculation procedure proposed in this paper is consistent with critically-selected experimental data. It was demonstrated that it is possible to use ΦF(I) for predicting the thermodynamic equilibrium parameters independently of Pearson's hardness of acids and bases. O coeficiente de atividade molar individual do íon fluoreto (yF) foi determinado a 25° C para valores de força iônica entre 0,100 and 3,00 mol L-1 (NaClO4) usando-se um eletrodo íon-seletivo. A dependência do coeficiente de atividade com a força iônica é explicada pela equação ΦF = log yF = 0,2315I - 0,041I². A função ΦF(I), foi associada a outras funções estimadas em trabalhos anteriores, por exemplo,ΦCu(I) para cobre, e ΦH(I) para íon hidrogênio, possibilitando a estimativa de constantes de estabilidade estequiométricas e termodinâmicas tanto para equilíbrios de protonação de alguns haletos e pseudo-haletos como para as constantes de formação de complexos 1:1 de metais bivalentes com fluoreto e pseudo-haletos. O procedimento de cálculo proposto é consistente com dados experimentais criticamente selecionados da literatura. Verificou-se que é possível usar ΦF(I) na previsão de parâmetros de equilíbrio termodinâmicos independentemente do caráter HSAB de Pearson .