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This work reports the development of a novel green analytical procedure for the determination of total anionic surfactants in waters. The method was based on the replacement of CHCl 3 by polyurethane foam (PUF) for the extraction of an ionic-pair formed between methylene blue (MB + ) and anionic surfactants. Besides, colored species retained on PUF were measured directly on the foam surface by treating digital images recorded with a scanner. Several parameters that could affect the performance of the method were evaluated. At optimum conditions, the concentration of MB + used was 1.7 × 10 − 5 mol L − 1 , PUF mass was 50 mg and shaking time was 15 min. Collection parameters related to the analysis of digital images presented no significant influence on the method. The application of the proposed method in the analysis of river waters was only possible after adjustment of the ionic strength and pH of the standard solutions and samples with a 0.01 mol L − 1 phosphate buffer solution with pH 7.5. The limit of quantification was 0.14 mg L − 1 , enough to attend the Brazilian legislation regarding the maximum concentration permitted of total anionic surfactant in surface waters. The developed method was compared with a standard method and presented no significant difference at 95% confidence level. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a study was performed to evaluate the use of Amberlite XAD resins (XAD-2, XAD-4 and XAD-16), for the first time, as filling materials for low-density polyethylene membranes, which will be inserted as passive samplers for polycyclic aromatic hydrocarbons (PAHs) in gas phase. The use of samplers deployed for 48h evidenced a relative capability to retain the compounds under study. A detailed study was performed to evaluate the recovery of analytes from the sampler through microwave-assisted extraction by using acetonitrile. A clean-up step using alumina-C18 cartridges was necessary before determination of the PAHs by high performance liquid chromatography with fluorescence detection. The limits of detection were of the order of μgL−1 with relative standard deviation values that varied from 1 to 16% as a function of the compound and the XAD resin employed. Amberlite XAD resins can be considered an excellent alternative as filling material of semipermeable membrane devices for passive sampling of PAHs in air due to their low cost, ease of manipulation and suitable chemical and mechanical characteristics. [Copyright &y& Elsevier]

[Display omitted] • Low-cost alternative composite sensors using PLA, Al 2 O 3, and graphite. • Al 2 O 3 significantly improves the electrochemical properties of the sensors. • Determination of minoxidil by batch injection analysis is proposed for the first time. • Superior analytical performance than expensive sensors was achieved. • Electrochemical results statistically comparable to the UV–vis spectrometry. The development of new sensors, which are low-cost, portable, and disposable, is currently highly required. In this sense, this work describes a simple way for lab-made fabrication of new composite electrodes exploiting an environmental friendly matrix based on thermoplastic polylactic acid (PLA). Great conductive features were achieved using graphite and aluminum oxide in PLA. The amount of aluminum oxide has been carefully optimized (0 to 12.25 % m/m). The manufacturing process presented reproducibility (between-device % relative standard deviation (RSD) < 7.3). Additionally, the electrode was characterized by electrochemical, spectroscopy, and morphological techniques. Improved cyclic voltammetric responses regarding I pa, I pc, and Δ E p were obtained towards the detection of the redox probes [Fe(CN) 6 ]3-/4- and dopamine using the electrode incorporated with aluminum oxide. Moreover, electrochemical impedance measurements revealed a more facilitated charge transfer process in the alumina-loaded electrode (Rct = 2070 Ω) than without alumina (Rct = 2810 Ω). The developed sensor was associated with batch injection analysis for the simple, fast, and sensitive amperometric monitoring of minoxidil (MXD) in pharmaceuticals, achieving a greater sensitivity with a detection limit of 2.9 µmol/L. A wide linear behavior from 10 to 1000 µmol/L and a between-measurement % RSD of less than 6 were acquired. Also, the method is free of interference from compounds commonly used as excipients in pharmaceutical products. When applied to the pharmaceutical sample, results statistically comparable to the reference method (UV–Vis spectrometry) were achieved, which confirmed the method's accuracy. Thus, the proposed sensor proves to be a powerful alternative tool for MXD monitoring, providing comparable and even better results with other high-cost electrochemical sensors. [ABSTRACT FROM AUTHOR]

The electrochemical process involving primaquine was studied at a glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (MWCNT). The GC/MWCNTs electrode promoted an intense oxidation peak for primaquine, improving signal when compared to the one observed using bare GC as electrode. Besides the increasing in active electrode area, the MWCNTs seemed to provide faster electron transfer. The linear analytical response for primaquine, in the concentration range from 0.1 to 5.0 μmol L−1, was achieved on a supporting electrolyte consisting of Britton-Robinson buffer (0.02 mol L−1; pH 7.00) and KCl (0.25 mol L−1). The quantitative assay using square-wave voltammetry was performed by successive additions of standard into the electrochemical cell, containing the sample, with instrumental limit of detection (LOD) of 7.3 μg L−1 (28 nmol L−1). A procedure involving liquid-liquid extraction and thin-layer chromatography provided selectivity and pre-concentration required for the determination of traces of primaquine in urine samples (LOD of the method of 146 ng L−1). Recoveries in urine samples were statistically similar to the one achieved by HPLC. • Modification of glass carbon by MWNCTs amplified analytical response of primaquine. • Voltammetry associated to thin-layer chromatography was used to determine primaquine. • Limit of detection of 146 ng L−1 was adequate for urine analysis. • MWCNTs enabled peak resolution to identify steps in the primaquine redox process. [ABSTRACT FROM AUTHOR]