Adriana G. Lista

A simple and rapid capillary electrophoretic method was developed for the simultaneous determination of two sulfonylurea herbicides in water samples: metsulfuron-methyl (MSM) and nicosulfuron (NS). These herbicides are widely used in agricultural practices and their residues represent potential environment pollutants in waters and soils. The effect of the pH of the background electrolyte solution (BGE), the percentage of methanol in the BGE and the separation voltage were studied on the resolution of MSM and NS. A 2³ factorial design was used to identify the main factors which significantly influenced the separation of these compounds. Other parameters were evaluated by the univariate method. The experimental results show that using a BGE composed of 25 mmol·L⁻¹ sodium borate and 3% (v/v) of methanol at pH 8.5 and applying 15 kV, satisfactory analysis time and resolution between peaks can be obtained. The linear range for both analytes was 0.1–2.0 µg·mL⁻¹. The detection limits were 0.034 µg·mL⁻¹ for MSM and 0.044 µg·mL⁻¹ for NS. Surface water and groundwater samples were analyzed applying the new method, and the obtained results presented satisfactory recovery percentages (82%–102%).

A simple in‐line single drop liquid‐liquid‐liquid microextraction (SD‐LLLME) coupled with capillary electrophoresis (CE) for the determination of two fluoroquinolones was developed. The method is capable to quantify trace amount of analytes in water samples and to improve the sensitivity of CE detection. For the SD‐LLLME, a thin layer of organic phase was used to separate a drop of 0.1 M NaOH hanging at the inlet of the capillary from the aqueous donor phase. By this way, the analytes were extracted to the acceptor phase through the organic layer based on their acidic/basic dissociation equilibrium. The drop was immersed into the organic phase during 10 min for extraction and then it is directly injected into the capillary for the analysis. Parameters such as type and volume of organic solvent phase, aqueous donor and acceptor phases and extraction time and temperature were optimized. The enrichment factor was calculated, resulting 40‐fold for enrofloxacin (ENR) and 6‐fold for ciprofloxacin (CIP). The linear range were 20–400 μg·L⁻¹ for ENR and 60–400 μg·L⁻¹ for CIP. The detection limits were 10.1 μg·L⁻¹ and 55.3 μg·L⁻¹ for ENR and CIP respectively and a good reproducibility was obtained (4.4% for ENR and 5.6% for CIP). Two real water samples were analysed applying the new method and the obtained results presented satisfactory recovery percentages (90–100.3%). This article is protected by copyright. All rights reserved

Multiwall carbon nanotubes (MWCNTs) were oxidized with different agents and a characterization study was carried out. Then, hybrid‐magnetic nanoparticles (HMNPs) were synthesized as iron oxide supported on the selected multiwalled carbon nanotubes (MWCNTs‐Fe₃O₄) obtained from MWCNTs oxidized with HNO₃. The HMNPs characterization revealed the presence of iron oxide as magnetite onto the MWCNTs surfaces. These HMNPs were used for arsenic removal from groundwater. The adsorption process variables were optimized (concentration of NPs, contact time, and pH), and these systems could remove 39.93 mg As/g adsorbent. Therefore, these nanoparticles appear as a good alternative for removing arsenic from water samples.

A method to determine four antibiotics for veterinary use (ciprofloxacin, enrofloxacin, florfenicol, and chloramphenicol) of different families (fluoroquinolones and amphenicols) in bovine milk was developed. The determination of the analytes was carried out using micellar electrokinetic capillary chromatography (MEKC) with a common sodium borate‐SDS buffer solution containing single‐walled carbon nanotubes (SWCNTs). In this way, a great improvement in the electrophoretic resolution and the separation efficiency was achieved compared to MEKC. An online reverse electrode polarity‐stacking mode (REPSM) was carried out to enhance sensitivity. This step was performed in only 2 min and it allowed a stacked percentage of 103. That means that all the amount of injected analytes is effectively stacked. When this stacking procedure was combined with an off‐line preconcentration step, based on SPE, analytes could be detected in lower concentration than the established maximum residue limits (MRLs). The LODs for the four compounds were between 6.8 and 13.8 μg L⁻¹ and the RSD values were between 1.1% and 6.6%. The whole method was applied to spiked real samples with acceptable precision and satisfactory recoveries.

In order to improve the quality control of dehydrated broth, a new automated method was developed to determine total creatinine in dehydrated broths. The sample pretreatment was coupled on‐line with the Flow Injection Analysis (FIA) system for analyte determination by the classical Jaffé reaction, stopped flow methodology, and spectrophotometric detection. The time consumed was reduced from 7 h, which is necessary with the official method, to 25 min. The calibration graph is linear between 0.342–1.368 mg creatinine/100 mL. The relative standard deviation (RSD%) was 1.7%, the sample throughput was 7 h⁻¹, and the detection limit was 0.185 mg creatinine/100 mL. The validation of the proposed method was carried out with real samples. The obtained results were compared with those obtained from the Association of Official Analytical Chemists (AOAC) reference method.