Comparação de procedimentos de quantificação de nitrato em tecido vegetal

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

Determination of Cd(II), Cu(II) and Ni(II) in aqueous samples by ICP-OES after on-line preconcentration in column packed with silica modified with 2-aminothiazole

This work describes the synthesis and characterization of 2-aminothiazole modified silica gel (SiAT) and the studies of adsorption and pre-concentration (in batch and using a flow-injection system coupled with optical emission spectrometer) of Cd(II), Cu(II) and Ni(II) in aqueous medium. The adsorption capacity for each metal ions in mmolg(-1) was: Cu(II) = 1.18, Ni(II) = 1.15 and Cd(II) = 1.10. The results obtained in the flow experiments showed about 100% of recovering of the metal ions adsorbed in a mini-column packed with 100 mg of SiAT, using 100 mu L of 2.0 mol L-1 HCl solution as eluent. The quantitative sorption-desorption of the metal ions made possible the application of a flow-injection system in the pre-concentration and quantification by ICP-OES of metal ions at trace level in natural water samples.

Determination of Cu, Ni, and Zn in fuel ethanol by FAAS after enrichment in column packed with 2-aminothiazole-modified silica gel

This work describes the synthesis and characterization of 2-aminothiazole-modified silica gel (SiAT), as well as its application for preconcentration (in batch and column technique) of Cu(II), Ni(II) and Zn(II) in ethanol medium. The adsorption capacities of SiAT determined for each metal ion were (mmol g(-1)): Cu(II)=1.20, Ni(II)=1.10 and Zn(II)=0.90. In addition, results obtained in flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 500 mg of SiAT. The eluent was 2.0 mol L-1 HCl. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in fuel ethanol using flame AAS for their quantification.

Dynamics of vibrating systems with tuned liquid column dampers and limited power supply

Tuned liquid column dampers are U-tubes filled with some liquid, acting as an active vibration damper in structures of engineering interest like buildings and bridges. We study the effect of a tuned liquid column damper in a vibrating system consisting of a cart which vibrates under driving by a source with limited power supply (non-ideal excitation). The effect of a liquid damper is studied in some dynamical regimes characterized by coexistence of both periodic and chaotic motion. (c) 2005 Elsevier Ltd. All rights reserved.

External polyacrylate-coating as alternative material for preparation of photopolymerized sol-gel monolithic column

Photopolymerized sol-gel monolithic columns for use in capillary electrochromatography were prepared in 125 mu m i.d. polyacrylate-coated fused-silica capillaries. The polyacrylate-coating, unlike the polyimide one, is transparent to the radiation used (approximate to 370 nm), and thus, no coating removal is necessary. This is a very important particularity since intrinsic capillary column characteristics, such as flexibility and mechanical resistance, are unchanged. A mixture containing metacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photoinitiator was irradiated at 370 nm for 20 min inside the capillaries to prepare the columns through sol-gel approach. The versatility and viability of the use of polyacrilate as a new capillary external coating were shown through preparation of two columns under different conditions, which were tested in electrochromatography for separation of standard mixture containing thiourea (marker compound), propylbenzene, phenanthrene and pyrene. (C) 2008 Elsevier B.V. All rights reserved.

Vertical distribution of zooplankton in the water column of Lago Amapá, Rio Branco, Acre, Brazil

O objetivo desta investigação foi observar a distribuição vertical da comunidade do zooplâncton no Lago Amapá (10º2'36S e 67º50'24W), localizado na planície de inundação do Rio Acre. Amostragens foram conduzidas em três diferentes profundidades da coluna da água, considerando aspectos sazonais do zooplâncton, parâmetros físicos, químicos e biológicos. Coletas foram realizadas semanalmente com Garrafa de Van Dorn. As espécies apresentaram maiores concentrações no meio da coluna da água. Foram encontradas 38 espécies, assim distribuídas: Rotifera (30), Cladocera (5) e Cyclopoida (3). A temperatura da coluna da água em geral apresentou-se alta, em torno de 30ºC, com pequena variação, resultando em baixa viscosidade. O índice de Jaccard, comparando-se as três estações de coletas, demonstrou que durante a fase de águas baixas, as estações 1 e 3 foram as mais similares (Cj = 0.7058), especialmente no meio da coluna da água. Lago Amapá apresentou características em conformidade com o Modelo do Distúrbio Intermediário, favorecendo a colonização de grupos oportunistas, tais como rotíferos.

Analysis of organochlorine pesticides in plain milk using direct injection on an ISRP column, with column switching

A simple and rapid procedure for extraction and separation from aldrin, DDT, endrin, heptachloro- and methoxychloro-organochlorine pesticides in raw milk has been developed by direct injection into an HPLC system without pretreatment of the samples, using an ISRP column.

On-line extraction and determination of carbofuran in raw milk by direct HPLC injection on an ISRP column

A method has been developed for extraction and determination of carbofuran in milk. The method involved direct injection of raw milk on to a human serum albumin dimethyloctyl-silica gel (HSA-Cs) column and the use of 80:20 (v/v) 0.01 M phosphate buffer pH 5.5 - acetonitrile as mobile phase. UV spectrophotometric detection was performed at 220 nm. Identification was based on retention time. Quantification was performed by automatic peak-area determination and was calibrated by use of an external standard.

Row-column response surface designs

Factorial experiments are widely used in industry to investigate the effects of process factors on quality response variables. Many food processes, for example, are not only subject to variation between days, but also between different times of the day. Removing this variation using blocking factors leads to row-column designs. In this paper, an algorithm is described for constructing factorial row-column designs when the factors are quantitative, and the data are to be analysed by fitting a polynomial model. The row-column designs are constructed using an iterative interchange search, where interchanges that result in an improvement in the weighted mean of the efficiency factors corresponding to the parameters of interest are accepted. Some examples illustrating the performance of the algorithm are given.

Pre-concentration of Cd(II), Cr(III), Cu(II) and Ni(II) on a column packed with oxycellulose.

Oxycellulose (OXICEL) was packed in a glass column to pre-concentrate metal cations from aqueous solutions. The pre-concentrated metal cations are directly eluted from the column using 5.0 mL of 1.0 mol L(-1) hydrochloric acid. The optimum pre-concentration conditions are given and the retention efficency achieved is higher than 95%. The enrichment factor is 10 for sample volumes of 50 mL.

A column generation approach to capacitated p-median problems

The Capacitated p-median problem (CPMP) seeks to solve the optimal location of p facilities, considering distances and capacities for the service to be given by each median. In this paper we present a column generation approach to CPMP. The identified restricted master problem optimizes the covering of 1-median clusters satisfying the capacity constraints, and new columns are generated considering knapsack subproblems. The Lagrangean/surrogate relaxation has been used recently to accelerate subgradient like methods. In this work the Lagrangean/surrogate relaxation is directly identified from the master problem dual and provides new bounds and new productive columns through a modified knapsack subproblem. The overall column generation process is accelerated, even when multiple pricing is observed. Computational tests are presented using instances taken from real data from Sao Jose dos Campos' city.

Determination of cocaine in samples of hair using the chromatographic column, ISRP-C-18

A method has been developed for the determination of the cocaine levels in samples of hair, using a chromatographic column internal surface reverse phase (ISRP)-C-18, for direct injection of the extracts of hair, without purification or derivation of the sample. The method allows monitoring an individual stopped for using or making cocaine. This method allowed the determination of levels of cocaine concentration in 75% of the analyzed samples of chemical dependents' hair, with cocaine detected at levels of 0.37-16.85 mug g(-1). In the other analyzed samples (25%), the drug was not detected, because the corresponding individuals told us that they consumed cocaine infrequently and in small amounts. The detection

Pre-concentration of Cd(II), Cr(III), Cu(II) and Ni(II) on a column packed with free carboxymethylcellulose (CMCH)

Carboxymethylcellulose packed in to a glass column was used to pre-concentrate metallic cations from aqueous solutions. The pre-concentrated metal cations are directly eluted from the column using 5.0 mL of 1.0 mol L -1 hydrochloric acid. The optimum pre-concentration conditions are given (glass column, 16 cm length, 0.80 cm i.d., stationary phase height of 12 cm, flow-rate, 1.5 mL min -1). The recuperation efficiency achieved is greater than 95%, while the enrichment factor is 10 for 50 mL of solution (0.50 mg L -1 each).