Jaim Lichtig

Heavy metal distribution in recent sediments of the Tietê-Pinheiros river system in São Paulo state, Brazil

Abstract The concentrations and possible chemical associations of Al, Fe, Mn, Ca, Cu, Pb, Cd, Zn, Ni and Cr in sediments of the Tiete-Pinheiros river system in Sao Paulo state, Brazil, were studied using a 3-step sequential extraction protocol recommended by the Standards, Measurements and Testing Programme (SM&T, formerly BCR). A single extraction with 0.1 mol l−1 HCl was applied in parallel to anoxic and air-dried samples. The river system crosses the metropolitan area of Sao Paulo (MASP), which houses a population of nearly 17 million people, and receives a large load of industrial and domestic wastes. Samples were collected from reservoirs in the surroundings of MASP, named Billings, Pirapora and Rasgao, and from the Barra Bonita reservoir, that is located in the Tiete river, 270 km downstream from Sao Paulo city. The distribution of metals indicates the recent pollution characteristics for samples from the Billings, Pirapora and Rasgao reservoirs. In these sediments the metals are associated to a large degree with reactive forms such as sulphides and carbonates, or adsorbed to amorphous oxyhydroxides of Fe and Mn. In samples from Barra Bonita, heavy metals are mainly associated with the residual fraction, suggesting that their concentrations are controlled significantly by transport processes with fine particles as carriers from diffuse pollution sources.

Determination of total protein by spectrophotometry: advantages and disadvantages of proposed methods

Spectrophotometric determination of total protein is used in several areas such as clinical analysis, food science and technology, biochemistry, protein chemistry, physiology. Five spectrophotometric methods are mostly used: biuret, Lowry, Bradford, Smith and UV absorption. In this review a general overview of these methods is presented (interferences, applications); other methodologies are also discussed.

PCDD/F, PCB and PAH content of brazilian compost

The level of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/F), polychlorinated biphenyls (PCB) and polycondensated aromatic hydrocarbons (PAH) in compost of different degree of maturation from 21 Brazilian municipal solid waste (MSW) compositing plants has been evaluated. The study shows that most PCDD/F concentrations are above the levels acceptable in Baden-Württemberg (FRG), being 17 ng I-TE/kg, especially for compost from metropolitan areas. These results are similar to those found for Germany. For PCB, the average of the sum of the concentrations of the six congeners PCB 28, 52, 101, 138, 153 and 180 is about 3 times lower in relation to German samples being less than the value indicated by the Baden-Württemberg legislation (0.2 mg/kg).

Construction and evaluation of a flow-through cell adapted to a commercial static mercury drop electrode (SMDE) to study the adsorption of Cd(II) and Pb(II) on vermiculite

This paper describes the construction and application of a robust flow-through cell for use with the capillary of a commercial static mercury drop electrode. Linearity of peak current was observed up to 0.50 mumol l(-1) for Cd(II) or Pb(II) in anodic stripping voltammetry experiments performed under continuous flow during the deposition step, using 120 s of deposition time and flow rate of 4.0 ml min(-1). Under these conditions the limits of detection for Cd(II) and Pb(II) were 13 and 17 nmol l(-1), respectively. An analytical throughput of 20 analyses per h was possible using 10 s for cleaning the cell between two samples and including the time needed for the potential scan, which was performed with the flow stopped, using the differential pulse mode for current sampling. The linear dynamic range can be extended up to 5 mumol l(-1) for both cations if the deposition time is decreased to 30 s, a condition in which the sampling throughput is 35 analyses per h. The proposed manifold was used to study the adsorption rates of Cd(II) and Pb(II) onto vermiculite at different pHs, allowing one to perform high sensitivity measurements at high sampling frequency, using low cost instrumentation.

Qualidade de medições em química analítica. Estudo de caso: determinação de cádmio por espectrofotometria de absorção atômica com chama

Calculation of uncertainty of results represents the new paradigm in the area of the quality of measurements in laboratories. The guidance on the Expression of Uncertainty in Measurement of the ISO / International Organization for Standardization assumes that the analyst is being asked to give a parameter that characterizes the range of the values that could reasonably be associated with the result of the measurement. In practice, the uncertainty of the analytical result may arise from many possible sources: sampling, sample preparation, matrix effects, equipments, standards and reference materials, among others. This paper suggests a procedure for calculation of uncertainties components of an analytical result due to sample preparation (uncertainty of weights and volumetric equipment) and instrument analytical signal (calibration uncertainty). A numerical example is carefully explained based on measurements obtained for cadmium determination by flame atomic absorption spectrophotometry. Results obtained for components of total uncertainty showed that the main contribution to the analytical result was the calibration procedure.

Extração seletiva de metais pesados em sedimentos de fundo do Rio Tietê, São Paulo

Sediment samples from Tiete river were submitted to chemical and sequential extractions of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn). It was followed a single extraction by using 0.1 mol L-1 hydrochloric acid and a sequential procedure to evaluate possible chemical associations described as exchangeable, carbonate, reducible oxides, sulfide, organic matter and residual fractions. High concentrations of heavy metals were determined at Pirapora reservoir, which is closer to the Metropolitan Area of Sao Paulo while for Barra Bonita reservoir, the results showed low concentrations for such elements. Acid volatile sulfides, grain size distribution and carbon contents were also determined.

Determination of secnidazol in pharmaceutical tablets and intestinal fluids by differential pulse polarography

Abstract A differential pulse polarography (DPP) method has been developed for quantitative determination of secnidazol in pharmaceutical tablets and intestinal fluids in a 0.04 M borate buffer. The reduction wave obtained showed that four electrons are involved in the process due to the reduction of the nitro group to hydroxilamine. In the lower pH range the protonated form of the hydroxilamino group is reduced to an amine group. The limiting current remains constant in a pH range of 3.5–5.8. In alkaline solutions the limiting current is significantly higher than a four electron reduction and limits to a six electron reduction, because it involves base catalysed dehydration of the hydroxilamino derivative formed in the first step yielding a ketimine, which is reduced in this conditions. The half-wave potentials are linearly shifted to more negative potentials with the increase of pH. The system is irreversible and controlled by diffusion. The determination of secnidazol in pharmaceutical preparations (Secnidal ® and intestinal fluids) were carried out employing DPP and compared with HPLC technique.

Determination of Cd, Pb and Ni by square wave stripping voltammetry in particulate matter collected in workplace atmosphere of some Brazilian industrial foundries

The concentration of Cd, Pb and Ni in atmospheric particulate matter collected in the workplace of three foundries located in the municipality of Loanda, Parana, Brazil, was determined by square wave voltammetry and ICP OES. The results show that workers are being systematically exposed to concentrations of Cd and Pb that are significantly above the Limit of Concentration recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). Results obtained by the proposed electroanalytical method do not differ statistically from the results obtained by ICP OES, indicating its potential application to environmental monitoring at much lower cost of installation, operation and maintenance. According to the results obtained, technological changes in the production process were recommended, as well as the use of personal protective equipment in order to keep the health and well being of workers, minimizing damages to the external environment.

Determinação de manganês em material particulado atmosférico de ambientes de trabalho utilizando eletrodo de diamante dopado com boro e voltametria de onda quadrada com redissolução catódica

A boron-doped diamond electrode is used for determination of Mn(II) in atmospheric particulate matter by square wave cathodic stripping voltammetry. The analytical curve was linear for Mn(II) concentrations between 5.0 and 37.5 µg L-1, with quantification limit of 3.6 µg L-1. The precision was evaluated by the relative standard deviation, with values between 5.1% and 9.3%. The electrode is free of adsorption, minimizing memory effects. Samples collected in the workplace atmosphere of a foundry had Mn(II) concentrations between 0.4 and 4 µg m-3. No significant differences were observed between the proposed method and inductively coupled plasma optical emission spectroscopy.

Iodometric standardization and biamperometric determination of iridium(IV).

Ir(IV) in the concentration range 0.4-0.8 g/l. can be easily determined iodometrically with 0.01M thiosulphate (starch as indicator). The relative standard deviation is 0.2-0.3%. When other coloured ions are present, biamperometric detection is recommended.