Lability of Cd, Cr, Cu, Mn and Pb complexed by aquatic humic substances

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determination of Hg in water by CVAAS using 2-aminothiazole modified silica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Heat transfer in packed beds: experimental evaluation of one-phase water flow

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Use of sugar cane bagasse as solid phase extractor for cadmium determination by FAAS

The present paper describes the use of sugar cane bagasse as solid phase extractor for cadmium determination after complexation of the analyte with ammonium diethyldithiophosphate (ADDP) and sorption of the Cd-DDP complexes on the solid support. The concomitants were separated using a flow injection analysis (FIA) system coupled to flame atomic absorption spectrometry (FAAS) for determination. The main parameters such as ADDP concentration, acid medium, flow rate, reaction coil length, and reaction time were investigated.The results obtained with HNO3 showed good accuracy and precision. The enhancement factor was 20.5 times for a 120-second preconcentration time, and the analytical frequency was 25 determinations per hour. The calibration curve was linear over the concentration range of 1-40 mu g L-1 Cd with a LOD of 0.697 mu g L-1 Cd and a relative standard deviation of 0.96% after 12 successive measurements of 30 mu g L-1 Cd.The proposed method was evaluated for the FIA-FAAS analysis of certified reference materials (tomato leaves, spinach leaves, and bovine liver) and Cd-spiked foods (shrimp, sardine, tuna, chicken liver and bovine liver). Good recoveries (80.0-97.1%) for the Cd-spiked samples and certified reference materials were obtained. The results of bagasse-packed minicolumns were compared with Si-C,8 packed minicolumns. The F-test was applied between Si-C-18/Bagasse minicolumns, Si-C-18/certified values, and bagasse/certified values. It was found that the results were in agreement with the certified values at a 95% confidence level.

Root growth and cotton nutrition as affected by liming and soil compaction

Soil columns were produced by filling PVC tubes with a Dark Red Latosol (Acrortox, 22% of clay). A compacted layer was established at the depth of 15 cm in the columns. In the compacted layer, soil was packed to 1.13, 1.32, 1.48, and 1.82 Mg kg(-1), resulting in cone resistances of 0.18, 0.43, 1.20, and 2.50 MPa. Cotton was cropped for 30 days. Lime was applied to raise base saturation to 40, 52, and 67%. The highest base saturation caused a decrease in phosphorus (P) and zinc (Zn) concentrations in the plants. A decrease in root dry matter, length and surface area was also observed. This could be a consequence of lime induced Zn deficiency. Root growth was decreased in the compacted layer, and complete inhibition was noticed at 2.50 MPa. Once the roots got through the compacted layer, there was a growth recovery in the bottom layer of the pots. The increase in base saturation up 52% was effective in preventing a decrease in cotton root length at soil resistances to 1.20 MPa. Where the roots were shorter, there was an increase in nutrient uptake per unit of root surface area, which kept the plants well nourished, except for P.

Determination of malic acid in real samples by using enzyme immobilized reactors and amperometric detection

The malate dehydrogenase (MDH) and ascorbate oxidase were immobilized independently, onto silanized controlled porous silica and packed in a tygon tube. The reactors were inserted in the flow system, and the malic acid was determined by measurement of NADH produced by enzymatic reaction. The NADH was reoxidized in a wall jet cell that consisted of spectrographic graphite, Ag/AgCl, KCl(sat), and steel needle as work, reference, and counter electrodes, respectively. The current intensities were measured at 390 mV. The malate calibration curve shows a linear range from 5.0 x 10(-6) to 1.0 x 10(-4) molL(-1), the lifetime was 40 analyses, after that a decrease of 20% on the response is observed. Three different citric juices were analyzed and a good correlation between the proposed method and spectrophotometric commercial kit were obtained.

Flow injection AAS determination of Cd, Cu, and Pb at trace levels in wine using solid phase extraction

A comparative study is reported between C-18 bonded silica gel and powdered polyethylene (PE) as sorbent for Cd, Cu, and Pb determination using ammonium diethyldithiophosphate (ADTP) as the complexing agent in a flow injection system. The complexes were formed in 0.14 mol L-1 HNO3 and processed in a simple flow system comprising a peristaltic pump, a manual injector-commutator, and a sorbent-packed minicolumn. Ethanol was selected as the eluent and analytes in the eluate were determined by flame atomic absorption spectrometry. The optimum concentration of the complexing agent was 0.1% (m/v) ADTP for Cu and Pb determination using either C-18 or PE, and 0.25% (m/v) ADTP for Cd determination using PE. The sample loading flow rates were 5.0, 3.6, and 3.0 mL min(-1) for Cu, Pb, and Cd, respectively. The best elution flow rate was 6.5 mL min(-1). For a 60-sec preconcentration time, the sampling rate was 40 h(-1) and the enrichment factors of 33, 36, and 11 times (C-18) or 18, 22, and 23 times (PE) were obtained for Cu, Pb, and Cd, respectively. The limits of detection (LOD) were 1.6 mug L-1 Cu, 11 mug L-1 Pb, and 2.0 mug L-1 Cd using C-18 or 2.9 mug L-1 Cu, 19 mug L-1 Pb, and 1.0 mug L-1 Cd using PE, respectively. The relative standard deviations (n = 12) were typically <2%, <2%, and <6% for Cd, Cu, and Pb, respectively. The recoveries of Cd, Cu, and Pb added to wine samples varied from 96-99%, 97-102%, and 90-99%, respectively, using C-18 or PE. Accuracy was checked for Cd, Cu, and Pb determination in six wine samples digested by block digestor and open-vessel microwave-assisted digestion systems. The results revealed that C-18 was more efficient for Cu and Pb determination, while PE was the best sorbent for Cd.

Multiresidue analysis of pesticides in water from rice cultures by on-line solid phase extraction followed by LC-DAD

An automated on-line solid phase extraction procedure followed by liquid chromatography with diode array detection was investigated for the determination of different classes of pesticides in water samples containing varied amount of humic substances. The different pesticides used were: carbendazin, carbofuran, atrazine, diuron, propanil, molinate, alachlor, parathion-ethyl, diazinon, trifluralin and the degradation products deisopropylatrazine and deethylatrazine. Humic substances extracted from a Brazilian sediment were used from 5 to 80 mg/l and their influence on recoveries was evaluated in neutral and acidic media. Recoveries higher than 70% were obtained for all the pesticides, from the preconcentration of 75 mi of aqueous sample fortified at 2 ng/ml using precolumns packed with PLRP-S. Good recoveries were obtained at neutral pH for most of the analytes up to 40 mg/l of humic acid. Only at 80 mg/l the recoveries were significantly affected, both at acidic and neutral pH. The method was applied to the determination of pesticides in river water spiked at 0.1 to 1 ng/ml. Detection limits obtained for water containing 10 mg/l of humic acid were between 0.05 and 0.3 ng/ml.

Determination of organochlorine pesticides and polychlorinated biphenyls residues in municipal solid waste compost by gas chromatography with electron-capture detection

A simple and efficient method for the simultaneous gas chromatographic determination of ten organochlorine pesticides (alpha-HCH, beta-HCH, gamma-HCH, p,p'-DDT, o,p'-DDT, p,p'-DDD, p,p'-DDE, aldrin, endrin, and dieldrin) and six congeners of PCBs (PCB 28, 52, 118, 138, 153, and 180) in municipal solid waste compost is described. The procedure involves a solid-phase dispersion matrix using celite as dispersant sorbent, alumina as clean up sorbent and hexane-dichloromethane (7:3, v/v) mixture as eluting solvent. An additional purification step with copper was necessary to eliminate sulphur. Analysis of the sample was performed by GC-ECD. The method was validated with fortified samples at two concentration levels (0.025 and 0.05 mg kg(-1)). Average recovery ranged from 77 to 121% with relative standard deviation between 1 and 18%. The detection limits, which ranged from 0.003 to 0.01 mg kg-1, were lower than those established by the Baden-Wurttemberg directive (0.033 mg kg(-1)).

Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preconcentration of heavy metals ions from aqueous solutions by means of cellulose phosphate: An application in water analysis

Cellulose phosphate (CELLPHOS) was studied as a collector for analytical preconcentration of traces of Cd(II), Cr(III), Cu(II) and Ni(II) from aqueous sample solution. It has been proved that using chromatographic columns packed with CELLPHOS for preconcentration and 1.0 mol 1 -1 HCl for elution the adsorbed analytes are quantitatively enriched. An enrichment factor of 20 (100 ml sample, 5 ml concentrate) was achieved by this separation procedure, which was applied to a series of water analyses (river, sea, bog water).

Determination of mercury in agroindustrial samples by flow-injection cold vapor atomic absorption spectrometry using ion exchange and reductive elution

A flow-injection system with a Chelite-S® cationic resin packed minicolumn is proposed for the determination of trace levels of mercury in agroindustrial samples by cold vapor atomic absorption spectrometry. Improved sensitivity and selectivity are attained since mercuric ions are on-line concentrated whereas other potential interferents are discarded. With on-line reductive elution procedure, concentrated hydrochloric acid could be replaced by 10% w/v SnCl2, in 6 M HCl as eluent. The reversed-intermittent stream either carries the atomic mercury, to the flow cell in the forward direction or removes the residue from reactor/gas liquid separator to a discarding flask in the opposite direction. Concentration and volume of reagent, acidity, flow rates, commutation times and potential interfering species were investigated. For 120 s preconcentration time, the proposed system handles about 25 samples h-1 (50.0 500 ng l-1), consuming about 10 ml sample and 5 mg SnCl2 per determination. The detection limit is 0.8 ng l-1 and the relative standard deviation (RSD) (n = 12) of a 76.7 ng l-1 sample is about 5%. Results are in agreement with certified value of standard materials at 95% confidence level and good recoveries (97-128%) of spiked samples were found. (C) 2000 Elsevier Science B.V.

Morphology changes induced by laser irradiation on disperse red 13 films prepared by physical vapor deposition

Surface morphology changes induced by argon laser irradiation (514 nm) on disperse red 13 (DR13) films prepared by physical vapor deposition (PVD) were investigated. Atomic force microscopy was used to characterize the irradiated sample for different periods of irradiation. Needle-shape structures are observed which are attributed to the symmetry of DR13 molecules. The film becomes increasingly closely packed with the irradiation, with lower root mean square roughness for long exposure times. This is due to photoisomerization of DR13 molecules and probably heating of the sample, which can provide the required mobility for the molecular rearrangement. The rearrangement is such that voids in the film are filled in upon irradiating the sample, thus decreasing the film roughness and increasing the packing.

Experimental analysis of heat transfer in packed beds with air flow

Heat-transfer studies were carried out in a packed bed of glass beads, cooled by the wall, through which air percolated. Tube-to-particle diameter ratios (D/dp) ranged from 1.8 to 55, while the air mass flux ranged from 0.204 to 2.422 kg/m2·s. The outlet bed temperature (TL) was measured by a brass ring-shaped sensor and by aligned thermocouples. The resulting radial temperature profiles differed statistically. Angular temperature fluctuations were observed through measurements made at 72 angular positions. These fluctuations do not follow a normal distribution around the mean for low ratios D/dp. The presence of a restraining screen, as well as the increasing distance between the temperature measuring device and the bed surface, distorts TL. The radial temperature profile at the bed entrance (T0) was measured by a ring-shaped sensor, and T 0 showed to be a function of the radial position, the particle diameter, and the fluid flow rate.

Determination of Cu, Ni and Pb in Aqueous Medium by FAAS after Pre-Concentration on 2-Aminothiazole Modified Silica Gel

This work describes the synthesis and characterization of 2-aminothiazole modified silica gel (SiAT), and the results of a study of the adsorption and pre-concentration (in batch and using a flow-injection system coupled to an absorption atomic spectrometer) of Cu(II), Ni(II) and Pb(II) in aqueous medium. The adsorption capacities for each metal ions in mmol g -1 were: Cu(II)= 1.18, Ni(II)= 1.15 and Pb(II)= 1.10. The results obtained in the flow experiments showed a recovery of practically 100% of the metal ions adsorbed in a mini-column packed with 100 mg of SiAT, using 100 μL of 2.0 mol L -1 HCl solution as eluent. The sorption-desorption of the metal ions made possible the application of a flow-injection system for the pre-concentration and quantification by FAAS of metal ions at trace level in natural water samples digested and not digest by an oxidizing UV photolysis.