Luciana Oliveira dos Santos

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.

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.

Development of a sequential injection chromatography (SIC) method for determination of simazine, atrazine, and propazine

This paper describes the development of a sequential injection chromatography (SIC) procedure for separation and quantification of the herbicides simazine, atrazine, and propazine exploring the low backpressure of a 2.5 cm long monolithic C(18) column. The separation of the three compounds was achieved in less than 90 s with resolution >1.5 using a mobile phase composed by ACN/1.25 mmol/L acetate buffer (pH 4.5) at the volumetric ratio of 35:65 and flow rate of 40 microL/s. Detection was made at 223 nm using a flow cell with 40 mm of optical path length. The LOD was 10 microg/L for the three triazines and the quantification limits were of 30 microg/L for simazine and propazine and 40 microg/L for atrazine. The sampling frequency is 27 samples per hour, consuming 1.1 mL of ACN per analysis. The proposed methodology was applied to spiked water samples and no statistically significant differences were observed in comparison to a conventional HPLC-UV method. The major metabolites of atrazine and other herbicides did not interfere in the analysis, being eluted from the column either together with the unretained peak, or at retention times well-resolved from the studied compounds.

Determination of picloram in waters by sequential injection chromatography with UV detection

This paper describes a sequential injection chromatography procedure for determination of picloram in waters exploring the low backpressure of a 2.5 cm long monolithic C18 column. Separation of the analyte from the matrix was achieved in less than 60 s using a mobile phase composed by 20:80 (v v-1) acetonitrile:5.0 mmol L-1 H3PO4 and flow rate of 30 μL s-1. Detection was made at 223 nm with a 40 mm optical path length cell. The limits of detection and quantification were 33 and 137 μg L-1, respectively. The proposed method is sensitive enough to monitor the maximum concentration level for picloram in drinking water (500 μg L-1). The sampling frequency is 60 analyses per hour, consuming only 300 μL of acetonitrile per analysis. The proposed methodology was applied to spiked river water samples and no statistically significant differences were observed in comparison to a conventional HPLC-UV method.

Application of sequential injection-square wave voltammetry (SI-SWV) to study the adsorption of atrazine onto a tropical soil sample.

Square wave voltammetry automated by sequential injection analysis was applied to determine the Freundlich adsorption coefficients for the adsorption of atrazine onto a clay rich soil. The detection limit in soil extracts was between 0.18 and 0.48mumolL(-1), depending on the medium used to prepare the extracts (0.010molL(-1) KCl, CaCl(2) or HNO(3) and 0.0050molL(-1) H(2)SO(4)), all of them conditioned in 40mmolL(-1) Britton-Robinson buffer at pH 2.0 in presence of 0.25molL(-1) NaNO(3). Also in soil extracts the linear dynamic range was between 1.16 and 18.5mumolL(-1) (0.25-4.0mugmL(-1)), with a sampling frequency of 190h(-1). The K(f) Freundlich adsorption coefficient was 3.8+/-0.2mumol(1-1/n)L(n)kg(-1) in medium of 0.010molL(-1) KCl or CaCl(2), but increased to 7.7+/-0.1 and 9.0+/-0.3mumol(1-1/n)L(n)kg(-1) in 0.010molL(-1) HNO(3) and 0.0050molL(-1) H(2)SO(4), respectively. The increase of K(f) was related to the decrease of pH from 6.4-6.7 in KCl and CaCl(2) to 3.7-4.0 in presence of HNO(3) or H(2)SO(4), which favors protonation of atrazine, facilitating electrostatic attractions with negative charges of the clay components of the soil. The 1/n parameters were between 0.76 and 0.86, indicating that the isotherms are not linear, suggesting the occurrence of chemisorption at specific adsorption sites. No statistically significant differences were observed in comparison to the adsorption coefficients obtained by HPLC. The advantage of the proposed SI-SWV method is the great saving of reagent because it does not use organic solvent as in the case of HPLC (50% (v/v) acetonitrile in the mobile phase). Additionally the start up of SI-SWV is immediate (no column conditioning necessary) and the analysis time is only 19s.

Developing a continuous flow-square wave voltammetry method for determination of atrazine in soil solutions using the hanging mercury drop electrode

This work describes the development of a Continuous Flow-Square Wave Voltammetry method for determination of atrazine using the hanging mercury drop electrode. The best signal to noise ratio was obtained at the square wave frequency of 350 Hz and flow rate of 0.47 mL min-1. Under these conditions, the analytical curve obtained in 0.010 mol L-1 CaCl2 soil extracts in presence of 40 mmol L-1 BR buffer and 0.25 mol L-1 NaNO3 was linear for atrazine concentrations between 0.10 and 2.0 µg mL-1, with detection and quantification limits of 0.030 and 0.10 µg mL-1, respectively. The proposed method increased the analytical throughput in comparison with the batch methodology, allowing a sampling frequency of 72 h-1 to be accomplished. Besides, the sample consumption is significantly reduced, and only 341 µL are necessary for each analysis. The results obtained were similar to the ones obtained by HPLC, but the proposed method is faster and does not use organic solvents.

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.

Uso do sistema âncora nas duas mãos e na mão não dominante reduz a oscilação corporal em idosos

The purpose of this study was to compare the effect of using the anchor system bilaterally and unilaterally (dominant and non-dominant hands), in older adults, in two visual conditions (with and without vision). Fourteen older adults were positioned in a semi-tandem position on a force plate, where they performed tasks under eight experimental conditions that employed the anchor system (two-handed, dominant hand, non-dominant hand, and without anchor), both with and without vision. The results, illustrated through the ellipse area adjusted to the displacement of the center of pressure (COP) and the mean sway velocity of the COP, showed that tasks performed with the anchor system held by both hands, and the anchor system held by the non-dominant hand, reduced both body sway and velocity when compared to the condition without the anchor. Furthermore, the task conditions with vision also reduced the ellipse area and the mean sway velocity. Overall, the anchor system is a tool that effectively allowed the older adults to decrease body sway. The effect of adding haptic information was similar throughout the different visual conditions tested, suggesting that the additional haptic information provided by the anchor system had a constant impact and did not vary with changes in the availability of vision. These results add new insights to the field of haptics when compared to findings of previous studies that use the light touch paradigm. Differences between the paradigms of light touch and the anchor system-and inter-hemispheric asymmetries in haptic perception tasks-were used to explain these insights.

Propriedades ácido-base e de complexação de ácidos húmico e fúlvico isolados de vermicomposto

Proton binding properties of humic and fulvic acids were studied by potentiometric titration. Carboxylic groups were the predominant ionizable sites in comparison to phenolic and amine groups. Total acidity of fulvic acid was 12 x 10-3 mol g-1, a number significantly higher than that obtained for humic acid (5.2 x 10-3 mol g-1). Copper ion binding was evaluated at pH 4, 5 and 6 by potentiometric titration with an ion selective electrode for Cu(II). Differential stability constants and complexation capacities were systematically higher for humic acid, despite its lower number of ionizable sites in comparison with fulvic acid.

Sequential injection analysis as a tool for on-line monitoring the sorption of fulvic acid onto modified vermiculite

This paper presents a sequential injection system associated with a tangential filtration unit and an ultraviolet detector for on-line monitoring of fulvic acid sorption onto two modified vermiculites. With the proposed approach it was possible to improve the temporal resolution in the investigation of the equilibrium time needed for the system sorbent-sorbate to reach the chemical equilibrium. Sorption onto a 10 g L-1 suspension of vermiculite material modified by intercalation of polyhydroxycations of Fe(III) was fast, reaching the equilibrium after 4 min of contact time, and resulting in sorption of 97.9 % of the initial 10 mg L-1 fulvic acid concentration. Sorption onto a 10 g L-1 suspension of an organic vermiculite which was modified by ion exchange with hexadecyltrimethylammonium bromide exhibited a fast initial rate of sorption, followed by desorption and re-adsorption processes, reaching the equilibrium after 30 min of contact time, with sorption of 98% of the initial 10 mg L-1 fulvic acid concentration.