Alex D. Batista

New sorbents for extraction and microextraction techniques

This review outlines recent progress in the research on some new classes of sorbents for extraction and microextraction techniques. Carbon nanotubes are allotropes of carbon with cylindrical structure. They are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Some applications of carbon nanotubes are presented in a perspective view. Molecular imprinting has proved to be an effective technique for the creation of recognition sites on a polymer scaffold. By a mechanism of molecular recognition, the molecularly imprinted polymers are used as selective tools for the development of various analytical techniques such as liquid chromatography, capillary electrochromatography, solid-phase extraction (SPE), binding assays and biosensors. Sol-gel chemistry provides a convenient pathway to create advanced material systems that can be effectively utilized to solve the solid phase microextraction fiber technology problems. This review is mainly focused on recent advanced developments in the design, synthesis and application of sol-gel in preparation of coatings for the SPME fibers.

On-line hyphenation of solid-phase extraction to chromatographic separation of sulfonamides with fused-core columns in sequential injection chromatography.

On-line sample pretreatment (clean-up and analyte preconcentration) is for the first time coupled to sequential injection chromatography. The approach combines anion-exchange solid-phase extraction and the highly effective pentafluorophenylpropyl (F5) fused-core particle column for separation of eight sulfonamide antibiotics with similar structures (sulfathiazole, sulfanilamide, sulfacetamide, sulfadiazine, sulfamerazine, sulfadimidine, sulfamethoxazole and sulfadimethoxine). The stationary phase was selected after a critical comparison of the performance achieved by three fused-core reversed phase columns (Ascentis(®) Express RP-Amide, Phenyl-Hexyl, and F5) and two monolithic columns (Chromolith(®) High Resolution RP-18 and CN). Acetonitrile and acetate buffer pH 5.0 at 0.60 mL min(-1) were used as mobile phase to perform the separations before spectrophotometric detection. The first mobile phase was successfully used as eluent from SPE column ensuring transfer of a narrow zone to the chromatographic column. Enrichment factors up to 39.2 were achieved with a 500 µL sample volume. The developed procedure showed analysis time <10.5 min, resolutions >1.83 with peak symmetry ≤1.52, LODs between 4.9 and 27 µg L(-1), linear response ranges from 30.0 to 1000.0 µg L(-1) (r(2)>0.996) and RSDs of peak heights <2.9% (n=6) at a 100 µg L(-1) level and enabled the screening control of freshwater samples contaminated at the 100 µg L(-1) level. The proposed approach expanded the analytical potentiality of SIC and avoided the time-consuming batch sample pretreatment step, thus minimizing risks of sample contamination and analyte losses.

A green flow-injection procedure for fluorimetric determination of bisphenol A in tap waters based on the inclusion complex with β-cyclodextrin

Bisphenol A, widely used in the production of plastics and found in the coating of food cans and baby bottles, shows estrogenic activity. The aim of the present work was to develop a flow system for the determination of bisphenol A in tap waters using the inclusion complex with β-cyclodextrin. The limit of detection was estimated at 1.5 μg L−1 (99.7% confidence level), and a linear response was verified between 5 and 320 μg L−1. The coefficient of variation and sampling rate were 1.5% (n = 20) and 78 h−1, respectively. Each analysis generated 1.9 mL of waste and consumed 45 µg of β-CD. The procedure is selective by exploiting a copperised zinc mini-column and on-line sample acidification to eliminate nitrate and carbonate interferences, respectively. The results for tap water samples (from 5.96 to 27.7 µg L−1) agreed with those obtained by HPLC at 95% confidence level. The procedure is environmentally friendly because it does not require organic solvents for sample clean-up or analyte concentration and minimises reagent consumption and waste generation.

On-column preconcentration in sequential injection chromatography: application to determination of parabens

Solid-phase extraction is the most usual technique for analyte preconcentration prior to liquid chromatographic analysis. It involves several time-consuming steps, including cartridge conditioning, sample loading and analyte elution. This work proposes on-column preconcentration in sequential injection chromatography by exploiting analyte retention at the head of the chromatographic column. A relatively high volume of an aqueous sample was carried to the reversed-phase column by water. After preconcentration, a suitable mobile phase was inserted to perform chromatographic separation. The feasibility of the proposed approach was demonstrated by preconcentration of parabens before chromatographic separation and UV detection. A linear response was achieved from 12.0 to 100.0 ng mL−1 (r2 > 0.998) with detection limits estimated to be 3.1, 3.3 and 4.6 ng mL−1 and enrichment factors of 435, 405 and 420 for methyl, ethyl, and propylparabens, respectively. Coefficients of variation for retention time and peak heights were below 2.2%. The proposed procedure can be applied to paraben extraction and preconcentration, presenting advantages such as minimization of analyte losses and contamination, reduction of organic solvent consumption and avoiding additional extraction cartridges.

A sub-minute electrophoretic method for simultaneous determination of naphazoline and zinc.

This paper reports for the first time, a method for simultaneous determination of naphazoline (NPZ) and zinc (Zn) using an analytical separation technique (capillary electrophoresis with capacitively coupled contactless conductivity detection -CE-C4D). A single run is possible every 55s (sampling rate=65h-1). The separation by CE-C4D was achieved on a fused silica capillary (50cm length - 10cm effective, 50μm i.d.) with a background electrolyte (BGE) composed by 20mmolL-1 of 2-(morpholin-4-yl)ethane-1-sulfonic acid (MES) and 20mmolL-1 of histidine (HIS) (pH 6.0). Detection limits were estimated at 20 and 30μmolL-1 and recovery values for spiked samples were 98 and 102% for NPZ and Zn, respectively. The developed procedure was compared to HPLC (NPZ) and FAAS (Zn) and no statistically significant differences were observed (95% confidence level).

A flow injection low-pressure chromatographic system exploiting fused-core columns

Chromatography with ultra-short monolithic columns, although attractive in view of its operation at low pressure without the need for expensive pumps, presents limited selectivity due to the low availability of stationary phases. In this work, fused-core columns are for the first time exploited in flow injection systems aimed at low-pressure chromatography. The proposed approach expands selectivity of flow injection low-pressure chromatography by considering the range of different stationary phases available for fused-core columns. Separation of methyl, ethyl and propylparabens was selected as an application and a critical comparison of chromatographic efficiencies of four columns (C18, RP-amide, F5 and phenyl-hexyl) is presented. An acetonitrile/phosphoric acid pH 2.5 solution was selected as the mobile phase, with specific ratios for each column. RP-amide provided the best chromatographic efficiency, performing quantitative separation of the three analytes in 8.0 min, with resolutions > 1.72, peak symmetry 0.996) and coefficients of variation of peak heights < 3.5% (n = 10). The procedure was applied to the determination of parabens in personal care products, and the results agreed with the HPLC reference procedure at the 95% confidence level.

Flow-based food analysis: an overview of recent contributions

Analysis of food and beverages (e.g. determination of nutrients, additives, and contaminants) is benefited by the advantages provided by flow systems such as high precision and sampling rate, as well as low reagent consumption and waste generation. Flow manifolds have been based on several detection techniques (e.g. luminescence, spectrophotometry, electroanalysis, and mass spectrometry), and have been employed for sample handling and chemical derivatization also coupled to separation techniques. Time-consuming steps such as sample preparation and calibration, including exploitation of the standard addition method have been performed on-line in a faster and cleaner way. In addition, flow systems are advantageous for the use of modified electrodes, biosensors, and optosensors. This review is focused on the critical evaluation of the potential of selected flow-based analytical systems for food analysis, highlighting the applications after 2012.

Fast and environmentally friendly determination of salicylic acid in plant materials by sequential injection chromatography

An improved procedure for determination of salicylic acid in plant materials is proposed. The phytohormone is extracted with water under microwave-assisted heating and the extract is directly analyzed by sequential injection chromatography with fluorimetric detection, thus avoiding time-consuming and wasteful sample clean-up steps. Isocratic elution (7 : 93 v/v acetonitrile/water) of the analyte was carried out in ca. 5 min, thus reducing the consumption of the organic solvent to 210 μL. A linear response was achieved from 0.5 to 8.0 mg L−1, which corresponds to 10 to 160 μg g−1 in the samples. The detection limit was estimated as 0.4 μg g−1, with a coefficient of variation of 1.2% (n = 20). The procedure was successfully applied to soybean, jackfruit, and sugarcane leaves, and results were in agreement with those obtained by HPLC at the 95% confidence level. The procedure is a fast and greener alternative for answering the high demand for this analysis in agronomical studies.