Solid-phase extraction in combination with large-volume sample stacking-capillary electrophoresis (SPE-LVSS-CE) was applied to measure chlortetracycline, doxycycline, oxytetracycline, and tetracycline in milk samples. Under optimal conditions, the proposed method had a linear range of 29 to 200 µg·L−1, with limits of detection ranging from 18.6 to 23.8 µg·L−1 with inter- and intraday repeatabilities < 10% (as a relative standard deviation) in all cases. The enrichment factors obtained were from 50.33 to 70.85 for all the TCs compared with a conventional capillary zone electrophoresis (CZE). This method is adequate to analyze tetracyclines below the most restrictive established maximum residue limits. The proposed method was employed in the analysis of 15 milk samples from different brands. Two of the tested samples were positive for the presence of oxytetracycline with concentrations of 95 and 126 µg·L−1. SPE-LVSS-CE is a robust, easy, and efficient strategy for online preconcentration of tetracycline residues in complex matrices.

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The use of veterinary drugs in medical treatments and in the livestock industry is a recurrent practice.

It is well known that Pb(II) is considered a highly toxic metal. The slight difference between toxic and permissible levels in drinking water is a matter of concern; therefore, highly sensitive and selective techniques have been proposed for quantification, such as the electrochemical ones. Here, an easy, simple, low-cost, and highly selective sensor based on carbon paste electrodes (CPE) and ion-imprinted polymers (IIP) is proposed for Pb(II) analysis in real water samples. Recognition cavities, selective to Pb(II), were synthesized based on a cross-linked polymer using vinyl pyridine. A modified CPE was constructed by a mixture of graphite powder, IIP, and paraffin oil. By voltammetry studies, a notable difference was observed in the electrochemical response of the electrodes modified with IIP and those with non-imprinted polymer (NIP), confirming the existence of the recognition cavities in the IIP. The construction and analysis parameters related to the analytical response Pb(II) (anodic current intensity of stripping voltammetry), were optimized; the selectivity was also studied considering potential interference ions. A linear concentration range from 3.3 mg l-1 to 33 mg l-1 and a limit of detection of 0.99 mg l-1 were achieved. Pb(II) was successfully quantified in real complex samples without previous treatment.

This paper presents the results concerning the first use of a polymer inclusion membrane (PIM) for the removal and transport of phenol from an aqueous solution and polluted water. The PIM contains Cyanex 923 as the carrier, cellulose triacetate (CTA) as the base polymer, and o-nitrophenyl pentyl ether (ONPPE) as a plasticizer. The effects of variables on the transport percentage of phenol have been studied. These variables include the concentration of the carrier and the plasticizer in the membrane, pH of the aqueous phase, and the concentration of NaOH in the stripping phase. This study shows that PIM composition has a great influence in phenol recovery, while the pH of the feed phase is a determining factor for the transport of phenol. In optimal conditions (PIM: 1 cm 3 ONPPE/g CTA, 0.5 M of Cyanex 923; feed phase: pH 2; stripping phase: NaOH 0.25 M), it is possible to transport 85% of phenol present in both the water lab feed phase and polluted water. Chemical oxygen demand (COD) shows that only 4.3% of organic compounds other than phenol are transported to the stripping phase, which indicates that the process is highly discriminative for phenol, even in extremely contaminated water.