Developing a fluorimetric sequential injection methodology to study adsorption/desorption of glyphosate on soil and sediment samples

This paper describes the development of a sequential injection method to automate the fluorimetric determination of glyphosate based on a first step of oxidation to glycine by hypochlorite at 48 degrees C, followed by reaction with the fluorogenic reagent o-phthaldialdehyde in presence of 2-mercaptoethanol in borate buffer (pH > 9) to produce a fluorescent 1-(2`-hydroxyethylthio)-2-N-alkylisoindole. The proposed method has a linear response for glyphosate concentrations between 0.25 and 25.0 mu mol L(-1), with limits of detection and quantification of 0.08 and 0.25 mu mol L(-1), respectively. The sampling rate of the method is 18 samples per hour, consuming only a fraction of reagents consumed by the chromatographic method based on the same chemistry. The method was applied to study adsorption/desorption properties in a soil and in a sediment sample. Adsorption and desorption isotherms were properly fitted by Freundlich and Langmuir equations, leading to adsorption capacities of 1384 +/- 26 and 295 +/- 30 mg kg(-1) for the soil and sediment samples, respectively. These values are consistent with the literature, with the larger adsorption capacity of the soil being explained by its larger content of clay minerals, while the sediment was predominantly sandy. (C) 2011 Elsevier B.V. All rights reserved.

Analytical Assessment of a Home Made Capillary Electrophoresis Equipment with Linear Charge Coupled Device for Visible Light Absorption Detection in the Determination of Food Dyes

The performance of modular home made capillary electrophoresis equipment with spectrophotometric detection, at a visible region by means of a miniaturized linear charge coupled device, was evaluated for the determination of four food dyes. This system presents a simple but efficient home made cell detection scheme. A computer program that converts the spectral data after each run into the electropherograms was developed to evaluate the analytical parameters. The dyes selected for analytical evaluation of the system were Brilliant Blue FCF, Fast Green FCF, Sunset Yellow FCF, and Amaranth. Separation was carried out in a 29cm length and 75 mu m I.D fused silica capillary, using 10mmolL-1 borate buffer at pH 9, with separation voltage of 7.5kV. The detection limits for the dyes were between 0.3 and 1.5mgL-1 and the method presented adequate linearity over the ranges studied, with correlation coefficients greater than 0.99. The method was applied for determination and quantification of these dyes in fruit juices and candies.

Effect of hydrogen charging on the stability of SAE 10B22 steel surface in alkaline solutions

The influence of hydrogen charging into a quenched and tempered boron steel membrane electrode (SAE 10B22) was studied using borate buffer (pH 8.4) and NaOH solutions (pH 12.7), with or without the addition of 0.01 M EDTA. At the hydrogen input side, hydrogen charging influenced cyclic voltammograms increasing the anodic charge of iron(II) hydroxide formation, and decreasing the donor density of passive films. These results suggest that the hydrogen ingress caused instability of metallic surface, increasing the surface area activity. (C) 2005 Elsevier Ltd. All rights reserved.

Local Electrochemical Investigation of Single Grains of Polycrystalline Cu-16%Zn-8%Al Alloy

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

Avaliação da disponibilidade de nitrogênio para milho em sucessão a gramíneas e leguminosas de cobertura

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparação e estudo eletroquímico de zinco sobre aço CFF e efeito de hidrogênio gerado in situ

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Métodos químicos para a estimativa do nitrogênio disponível do solo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise químico-farmacêutica e estudo de estabilidade e de dissolução de cápsulas de flucloxacilina sódica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Avaliação de inibidores voláteis de corrosão por técnicas eletroquímicas sobre o aço

Pós-graduação em Química - IQ

Characterization of the hemoglobins and globins of Synbranchus marmoratus Bloch, 1795 (Pisces, Synbranchidae)

1. 1. Total hemolysates of Synbranchus marmoratus Bloch, 1795, captured in Vitoriana, district of Botucatu, State of São Paulo, Brazil, were submitted to agar-starch gel electrophoresis on glass slides using 42 mM-Tris 1.7 mM EDTA-6.1 mM borate buffer, pH 8.8, for the gel and 10 mM borate-1.7 mM NaOH buffer, pH 8.6, for the cuvette. 2. 2. Three distinct hemoglobin bands were detected, with Hb I being of the cathodic type. 3. 3. Cellulose acetate electrophoresis in 800 mM Tris-2.1 mM EDTA buffer, pH 8.9, containing 6 M urea and 2.25 mM β-mercaptoethanol indicated the presence of four globin chains denoted α 1, α 2, β and γ. 4. 4. It is suggested that the probable tetrameric constitution of the hemoglobin of Synbranchus marmoratus Bloch, 1795 is Hb I (α 2 2γ 2), Hb II (α 2 1γ 2) and Hb III (α 2 1β 2). © 1986.

Identification of 48 homologues of phosphatidylethanol in blood by LC-ESI-MS/MS

Phosphatidylethanol (PEth) is an abnormal phospholipid carrying two fatty acid chains. It is only formed in the presence of ethanol via the action of phospholipase D (PLD). Its use as a biomarker for alcohol consumption is currently under investigation. Previous methods for the analysis of PEth included high-performance liquid chromatography (HPLC) coupled to an evaporative light scattering detector (ELSD), which is unspecific for the different homologues--improved methods are now based on time of flight mass spectrometry (TOF-MS) and tandem mass spectrometry (MS/MS). The intention of this work was to identify as many homologues of PEth as possible. A screening procedure using multiple-reaction monitoring (MRM) for the identified homologues has subsequently been established. For our investigations, autopsy blood samples collected from heavy drinkers were used. Phosphatidylpropanol 16:0/18:1 (internal standard) was added to the blood samples prior to liquid-liquid extraction using borate buffer (pH 9), 2-propanol and n-hexane. After evaporation, the samples were redissolved in the mobile phase and injected into the LC-MS/MS system. Compounds were separated on a Luna Phenyl Hexyl column (50 mm x 2 mm, 3 microm) by gradient elution, using 2 mM ammonium acetate and methanol/acetone (95/5; v/v). A total of 48 homologues of PEth could be identified by using precursor ion and enhanced product ion scans (EPI).

OPTIMIZING A SHORT-END ELECTROPHORETICALLY MEDIATED MICRO-ANALYSIS (EMMA) ASSAY FOR CREATININE

In this work electrophoretically mediated micro-analysis (EMMA) is used in conjunction with short end injection to improve the in-capillary Jaffé assay for creatinine. Key advances over prior work include (i) using simulation to ensure intimate overlap of reagent plugs, (ii) using OH- to drive the reaction, (iii) using short-end injection to minimize analysis time and in-line product degradation. The potential-driven overlapping time with the EMMA approach, as well as the borate buffer background electrolyte (BGE) concentration and pH are optimized with the short end approach. The best conditions for short-end analyses would not have been predicted by the prior long end work, owing to a complex interplay of separation time and product degradation rates. Raw peak areas and flow-adjusted peak areas for the Jaffé reaction product (at 505 nm) are used to assess the sensitivity of the short-end EMMA approach. Optimal overlap conditions depend heavily on local conductivity differences within the reagent zone(s), as these differences cause dramatic voltage field differences, which effect reagent overlap dynamics. Simul 5.0, a dynamic simulation program for capillary electrophoresis (CE) systems, is used to understand the ionic boundaries and profiles that give rise to the experimentally obtained data for EMMA analysis. Overall, fast migration of hydroxide ions from the picrate zone makes difficult reagent overlap. In addition, the challenges associated with the simultaneous overlapping of three reagent zones are considered, and experimental results validate the predictions made by the simulation. With one set of “optimized” conditions including OH- (253 mM) as the third reagent zone the response was linear with creatinine concentration (R2 = 0.998) and reproducible over the clinically relevant range (0.08 to 0.1 mM) of standard creatinine concentrations. An LOD (S/N = 3) of 0.02 mM and LOQ (S/N=10) of 0.08 mM were determined. A significant improvement (43%) in assay sensitivity was obtained compared to prior work that considered only two reagents in the overlap.

An MEKC assay for the therapeutic drug monitoring of cefepime

The development of a robust assay based on MEKC for cefepime in human serum and plasma with internal quality assurance is reported. Sample preparation comprises protein precipitation in the presence of SDS at pH 4.5. This is a gentle approach for which decomposition of cefepime during sample handling is negligible. After hydrodynamic sample injection of the supernatant, analysis occurs in a phosphate/borate buffer at pH 9.1 with 75 mM SDS using normal polarity and analyte detection at 257 nm. The MEKC run time interval and throughput are about 5 min and seven samples per hour, respectively. The calibration range for cefepime is 1-60 μg/mL, with 1 μg/mL being the LOQ. The performance of the assay with multilevel internal calibration was assessed with calibration and control samples. The assay is shown to be simple, inexpensive, reproducible, and robust. It was applied to determine cefepime levels in the sera of critically ill patients and to assess the instability of cefepime in patient and control samples. Our data revealed that serum containing cefepime can be stored at -20°C for a short time, whereas for long-term storage, samples have to be kept at -70°C.

Manufacturing DNA microarrays of high spot homogeneity and reduced background signal

Analyses on DNA microarrays depend considerably on spot quality and a low background signal of the glass support. By using betaine as an additive to a spotting solution made of saline sodium citrate, both the binding efficiency of spotted PCR products and the homogeneity of the DNA spots is improved significantly on aminated surfaces such as glass slides coated with the widely used poly-l-lysine or aminosilane. In addition, non-specific background signal is markedly diminished. Concomitantly, during the arraying procedure, the betaine reduces evaporation from the microtitre dish wells, which hold the PCR products. Subsequent blocking of the chip surface with succinic anhydride was improved considerably in the presence of the non-polar, non-aqueous solvent 1,2-dichloroethane and the acylating catalyst N-methylimidazole. This procedure prevents the overall background signal that occurs with the frequently applied aqueous solvent 1-methyl-2-pyrrolidone in borate buffer because of DNA that re-dissolves from spots during the blocking process, only to bind again across the entire glass surface.