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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. [ABSTRACT FROM AUTHOR]

Abstract: A magnetic solid phase extraction method coupled to capillary electrophoresis is proposed for the determination of tetracycline, oxytetracycline, chlortetracycline and doxycycline in milk samples. Five different magnetic phenyl silica adsorbents covered with magnetite were synthesized by varying the molar ratio of phenyltrimethylsilane and tetramethylorthosilicate; these adsorbents were evaluated in terms of their pH and degree of hydrophobicity for tetracycline retention. The optimal, selected combination of conditions was a pH of 10.0 and a magnetic sorbent ratio of 4:1; under these conditions, the retention capacity ranged from 99.7% to 101.2% for the four tetracyclines analyzed. The elution conditions and initial sample volume of the proposed extraction method were also optimized, and the best results were obtained with 1×10−3 M acetic acid in methanol as eluent and a 200ml of sample volume. Under optimal conditions, average recoveries ranged from 94.2% to 99.8% and the limits of detection ranged from 2 to 9μgl−1 for the four tetracyclines. After the proposed method was optimized and validated, 25 milk samples of different brands were analyzed, oxytetracycline residues were detected in five samples, in concentrations ranging from 98 to 213μgl−1. Subsequent analysis of positive samples by SPE–CE and magnetic solid phase extraction–HPLC revealed than no significant differences were found from results obtained by the proposed methodology. Thus, the developed magnetic extraction is a robust pre-concentration technique that can be coupled to other analytical methods for the quantitative determination of tetracyclines. [Copyright &y& Elsevier]

Abstract In this work, CdTe/CdS quantum dots were incorporated in a capillary electrophoresis system for the determination of glyphosate in soil samples. Fluorescence spectroscopic evaluation indicates there is an interaction between CdTe/CdS quantum dots and glyphosate, which produces an enhancement of the emission signal as a result of the formation of quantum dots-glyphosate complex. A capillary electrophoresis system for the separation of the complex from the remaining CdTe/CdS quantum dots is described herein. The variables involved in the separation were evaluated and optimized using a central composite design. Signals are elucidated under optimal conditions by calculating the difference in their electrophoretic mobility. The methodology selectivity allows the determination of glyphosate in complex matrices such as soil samples. The proposed method exhibits a linear range from 77.1 to 700 mg kg−1 with a limit of detection of 25.7 mg kg−1 and adequate repeatability and reproducibility (%RSD <5.0%). The described methodology was applied to 7 soil samples collected from crop fields in Hidalgo, Mexico, found concentrations varied from 320.6 to 607.7 mg kg−1. Highlights • CdTe/CdS quantum dots were characterized in presence of glyphosate. • CdTe/CdS quantum dots were incorporated in a CZE-LIF system for the determination of glyphosate. • The method was applied to soil samples. [ABSTRACT FROM AUTHOR]

• A method for the determination of malachite green and its leuco form was proposed. • The methodology consists on the use of modified henequen fibers as adsorbent in d-SPE. • The work proposes the use of copper phthalocyanine to modify the henequen fibers. • The methodology allowed the determination of both analytes using d-SPE-CE-DAD. • The methodology was applied in the analysis of fish samples with satisfactory results. A novel and simple procedure for the determination of malachite green (MG) and leuco-malachite green (LMG) in fish muscle was designed and validated. The method involved the use of henequen fibers modified with copper phthalocyanine as an efficient adsorbent in a dispersive-solid phase extraction technique. Following the extraction and pre-concentration process, CE-DAD was employed to quantify MG and LMG. The structural similarity of MG and LMG and the presence of the cationic forms under acidic conditions are the main drawbacks to determine these analytes in capillary electrophoresis. The proposed methodology allowed for the effective extraction and separation of both analytes using d-SPE-CE-DAD. The experimental parameters of the d-SPE technique were evaluated in order to get the highest pre-concentration efficiency. Under optimum conditions, the methodology achieves a limit of detection of 12.5 μg kg−1 for malachite green and 5.0 μg kg−1 for leuco-malachite green. Repeatability and reproducibility (%RSD n = 3) were less than 5.0% RSD in all cases, indicating that the method shows good precision for the analysis of real samples. In order to evaluate the accuracy of the method, the recovery was evaluated in tilapia samples at three concentration levels, recoveries varied from 88.7% to 109.5% for MG and from 65.3% to 88.8% for LMG. The method was validated and successfully applied to determine MG and LMG in fish samples. [ABSTRACT FROM AUTHOR]