Jorge C. Masini

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 atrazine using square wave voltammetry with the Hanging Mercury Drop Electrode (HMDE).

This paper presents the optimization of instrumental and solution parameters for determination of atrazine in river waters and formulation by square wave voltammetry (SWV) using a hanging mercury drop electrode. The best sensitivity (35.2+/-0.4muAmlmug(-1)) was achieved using a frequency of 400Hz and a medium composed of 40mmoll(-1) Britton-Robinson (BR) buffer at pH 1.9. The detection limit was 2mugl(-1) with a linear dynamic range between 10 and 250mugl(-1). Application of the method to real samples of river waters fortified with 10mugl(-1) of atrazine resulted recoveries between 92 and 116%. Additionally, good agreement was observed between results obtained by the proposed method and by HPLC for river water samples spiked with 25mugl(-1) of atrazine. The determination was not affected by the presence of humic acid at concentration of 5mgl(-1), indicating that interactions of the herbicide with this class of compounds are fully labile. The stability of the voltammetric signal for samples spiked with 250mugl(-1) atrazine was evaluated over a period of 14 days in four samples. For two samples, no systematic variation was observed, while for the other two, a decrease of peak current between 3 and 15% occurred, suggesting that the stability is dependent on the sample nature. HPLC analyses suggest formation of deethylatrazine during the second week of storage in the samples for which the SWV peak current had the more intense decrease.

Implementing stepwise solvent elution in sequential injection chromatography for fluorimetric determination of intracellular free amino acids in the microalgae Tetraselmis gracilis.

The concept of sequential injection chromatography (SIC) was exploited to automate the fluorimetric determination of amino acids after pre-column derivatization with o-phthaldialdehyde (OPA) in presence of 2-mercaptoethanol (2MCE) using a reverse phase monolithic C(18) stationary phase. The method is low-priced and based on five steps of isocratic elutions. The first step employs the mixture methanol: tetrahydrofuran: 10 mmol L(-1) phosphate buffer (pH 7.2) at the volumetric ratio of 8:1:91; the other steps use methanol: 10 mmol L(-1) phosphate buffer (pH 7.2) at volumetric ratios of 20:80, 35:65, 50:50 and 65:35. At a flow rate of 10 microL s(-1) a 25 mm long-column was able to separate aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), serine (Ser), glutamine (Gln), glycine (Gly), threonine (Thr), citruline (Ctr), arginine (Arg), alanine (Ala), tyrosine (Tyr), phenylalanine (Phe), ornithine (Orn) and lysine (Lys) with resolution >1.2 as well as methionine (Met) and valine (Val) with resolution of 0.6. Under these conditions isoleucine (Ile) and leucine (Leu) co-eluted. The entire cycle of amino acids derivatization, chromatographic separation and column conditioning at the end of separation lasted 25 min. At a flow rate of 40 microL s(-1) such time was reduced to 10 min at the cost of resolution worsening for the pairs Ctr/Arg and Orn/Lys. The detection limits varied from 0.092 micromol L(-1) for Tyr to 0.51 micromol L(-1) for Orn. The method was successfully applied to the determination of intracellular free amino acids in the green alga Tetraselmis gracilis during a period of seven days of cultivation. Samples spiked with known amounts of amino acids resulted in recoveries between 94 and 112%.

Complexation of Cd(II) and Pb(II) with humic acids studied by anodic stripping voltammetry using differential equilibrium functions and discrete site models

Abstract Binding of Cd(II) and Pb(II) to two humic acids was studied by differential pulse anodic stripping voltammetry using continuous differential equilibrium functions and linear Scatchard plots. One of the humic acids was a commercial sample from Aldrich (AHA) and the other was a sedimentary humic acid isolated from a Brazilian water reservoir (BBHA). The complexation study was performed at pH between 5 and 6 in 0.020 mol l −1 KNO 3 . The complexes were considered fully labile in the range of the metal to ligand concentration ratios studied, having diffusion coefficients ( D ML =1.3×10 −7 and 2.7×10 −7 cm 2 s −1 , for BBHA and AHA, respectively) smaller than the free cation [ D M =8×10 −6 and 7×10 −6 cm 2 s −1 for Cd(II) and Pb(II), respectively]. Differential equilibrium functions and the discrete site model led to similar interpretations of the experimental data. Binding of Pb(II) to both HA samples was stronger than for Cd(II), with a greater heterogeneity of binding sites. This was verified by the heterogeneity parameter, Γ, obtained from the differential equilibrium functions, as well as from the number of classes of binding sites used to fit the titration data to Scatchard plots.

Application of sequential injection-monosegmented flow analysis (SI-MSFA) to spectrophotometric determination of sulfide in simulated waters samples

This paper describes the coupling of sequential injection with monosegmented flow analysis (SI-MSFA) for determination of sulfide at typical concentrations in wastewaters. The method was based on the reaction of sulfide with 19 mmol l(-1) Fe(3+) and 3.63 mmol l(-1)N,N-dimethyl-p-phenylene diamine hydrochloride in medium of 1.1 mol l(-1) HCl, forming the dye methylene blue. The analytical curves were constructed by in-line dilution of a single stock standard solution. The robustness of the proposed method was checked constructing analytical curves in different working days and comparing the slopes, which had a relative standard deviation of 5.2% (n=5) for a concentration range between 0.17 and 1.0 mg l(-1) S(2-). The analytical throughput was 38 samples per h and the limit of detection was 0.040 mg l(-1). The feasibility of the SI-MSFA approach to perform standard additions for S(2-) determination was also described. Simulated samples spiked with known amounts of sulfide were analyzed by the proposed method, presenting recoveries between 70 and 115%. These results demonstrate the feasibility of the SI-MSFA method to perform in situ analysis of S(2-) in automatic monitoring stations.

Evaluation of neglecting electrostatic interactions on the determination and characterization of the ionizable sites in humic substances

Abstract The stoichiometry and pKa of the ionizable sites in humic acids has been determined by means of potentiometric titrations. The analytical implications of neglecting the free electrostatic energy that accompanies the proton dissociation in polyelectrolytes or humic acids is presented. Simulated titration curves of polyelectrolytes with known composition were generated according to an electrostatic model. The data of these titrations were treated by a linear calculation method developed for determination and characterization of weak monoprotic acids in mixtures. The influence of the polyelectrolyte molar mass was also studied. Besides, experimental titration curves of humic acids at ionic strength 0.010, 0.10 and 1.0 were peformed and the titration data were treated by the same calculation method. The results showed that the indication of the existence of two or three kinds of carboxylic groups in high-molar-mass polyelectrolytes may have been affected by a mathematical fit as consequence of ignoring electrostatic interactions. However, the experimental titrations data treatment have characterized five kinds of titratable groups which have concentration and pKas few affected by changes in the ionic strength. These results indicate that the chemical heterogeneity among groups with the same chemical nature is the major factor governing acid-base properties of humic acids having low charge accumulation.

Spectrophotometric determination of acid volatile sulfide in river sediments by sequential injection analysis exploiting the methylene blue reaction.

This paper demonstrates the application of sequential injection analysis to perform sulfide determination using the methylene blue chemistry, based on two reagents: 3.63 mmol l(-1)N,N dimethyl-p-phenylene diamine hydrochloride in 1.1 mol l(-1) HCl solution and 19 mmol l(-1) FeCl(3), also in 1.1 mol l(-1) HCl. These solutions are aspirated inside the holding coil of the sequential injection system as two reagent zones sandwiching the sample zone. Under optimized conditions, the detection limit was calculated at 40 mug l(-1) S(2-), with a linear dynamic range from 0.05 to 2 mg l(-1) S(2-). This linear range can be extended up to 32 mg l(-1) using in-line dilution for sulfide concentrations greater than 2 mg l(-1). The robust characteristic of the SI system with syringe pump leads to very stable analytical curves (precision of 4%), minimizing the laborious preparation of sulfide standards. The method was applied in the determination of acid volatile sulfide in river sediments.

Porous monoliths for on-line sample preparation: A review

This review aims at presenting the state of the art concerning monolithic materials for on-line sample preparation emphasizing solid-phase extraction, matrix exchange, and analyte conversion. Emphasis was given to organic and silica-based, as well as hybrid monoliths reported in the literature mostly after 2010. The first part of this review presents materials and strategies for enrichment of inorganic species in environmental and biological samples using mostly ICP-MS detectors. In the second part we focus on organic analytes, discussing the role of surface area of the polymer monoliths and density of adsorption sites for specific interactions, including incorporation of nanoparticles, metal organic frameworks, as well as the preparation of hybrid organic-silica monoliths to increase the surface area. Incorporation of ionic liquids to increase the number of types of interaction mechanisms available for retention is also discussed. Monoliths affording molecular recognition properties achieved by including boronate moieties for cis-diol recognition, as well as antibodies and aptamers for specific molecular recognition are also reviewed. The largest number of applications of molecular recognition mechanisms was observed for molecularly imprinted polymer monoliths as a consequence of the simplicity of this approach when compared to the use of immunosorbents or aptamers. The final part examines the on-line applications of immobilized enzyme reactors used for protein digestion in proteomic analysis and for kinetic studies in drug discovery and clinical assays usually coupling the reactors to mass spectrometers.

Determination of picloram in natural waters employing sequential injection square wave voltammetry using the hanging mercury drop electrode

This paper describes the development of a sequential injection analysis method to automate the determination of picloram by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800muL monosegment is formed, composed by 400muL of sample and 400muL of conditioning/standard solution, in medium of 0.10molL(-1) H(2)SO(4). Homogenization of the monosegment is achieved by three flow reversals. After homogenization the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50muLs(-1). After a suitable delay time, the potential is scanned from -0.5 to -1.0V versus Ag/AgCl at frequency of 300Hz and pulse height of 25mV. The linear dynamic range is observed for picloram concentrations between 0.10 and 2.50mgL(-1) fitting to the linear equation I(p)=(-2.19+/-0.03)C(picloram)+(0.096+/-0.039), with R(2)=0.9996, for which the slope is given in muALmg(-1). The detection and quantification limits are 0.036 and 0.12mgL(-1), respectively. The sampling frequency is 37h(-1) when the standard addition protocol is followed, but can be increased to 41h(-1) if the protocol to obtain in-line external calibration curve is used for quantification. The method was applied for determination of picloram in spiked water samples and the accuracy was evaluated by comparison with high performance liquid chromatography using molecular absorption at 220nm for detection. No evidences of statistically significant differences between the two methods were observed.

Sorption of atrazine, propazine, deethylatrazine, deisopropylatrazine and hydroxyatrazine onto organovermiculite

The interaction of atrazine (AT), propazine (PROP), deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (HAT) was studied with the clay mineral vermiculite saturated with K+ (VTK), and with the mineral modified by insertion of hexadecyltrimethyl-ammonium (HDTMA-VT) in the interlayer of VTK. The crude VTK exhibited negligible interaction with AT, PROP and DEA, moderate interaction with DIA and strong interaction with HAT. For the HDTMA-VT materials, removal percentages from aqueous medium for initial concentrations between 0.05 and 1.00 mg L-1 were 56 to 63% for AT, 43 to 45% for DEA, 12 to 19% for HAT and 77 to 78% for PROP. Sorption of AT, DEA and PROP onto HDTMA-VT was significantly enhanced in comparison to VTK. Ionic strength and pH had no significant influence on the sorption process. Desorption of all compounds from HDTMA-VT after 24 h of contact time was between 20 and 30% of the amount initially adsorbed.