We report on the time-resolved detection of the three fluoroquinolone (FQs) antibiotics ciprofloxacin (CIP), enrofloxacin (ENR) and flumequine (FLU). On addition of terbium(III) ions, the terbium(III)-FQs chelates are formed insitu in an on-capillary derivatization reaction of a microfluidic system. The laser-induced terbium(III)-sensitized luminescence of the chelates is measured at excitation/emission wavelengths of 337/545 nm. The analytes can be separated and quantified within less than 4 min. A solid phase extraction step for analyte preconcentration can be included prior to chelation and microchip capillary electrophoresis. The analytical ranges of the calibration graphs for CIP, ENR and FLU are from 10.6 to 60.0, 10.3 to 51.0, and 11.5 to 58.8 ng mL −1 , respectively, and the detection limits are 3.2, 3.1 and 3.6 ng mL −1 , respectively. The precision was established at two concentration levels of each analyte and revealed relative standard deviations in the range from 3.0 to 10.2 %. The method was applied to the analysis of FQ-spiked water samples.
We describe an on-chip microflow injection (μFI) approach for the determination of aminoglycoside antibiotics using chemiluminescence (CL) detection. The method is based on the inhibition of the Cu(II)-catalyzed CL reaction of luminol and hydrogen peroxide by the aminoglycosides due to the formation of a complex between the antibiotic and Cu(II). The main features of the method include small sample volumes and a fast response. Syringe pumps were used to insert the sample and the reagents into the microfluidic device. CL was collected using a fiber optic bundle connected to a luminescence detector. All instrumental, hydrodynamic and chemical variables involved in the system were optimized using neomycin as the aminoglycoside model. Inhibition is proportional to the concentration of the antibiotics. The dynamic ranges of the calibration graphs obtained for neomycin, streptomycin and amikacin are 0.3-3.3, 0.9-13.7, and 0.8-8.5 μmol L −1 , and the detection limits are 0.09, 0.28 and 0.24 μmol L −1 , respectively. The precision of the methods, expressed as relative standard deviation, is in the range from 0.8 to 5.0 %. The method was successfully applied to the determination of neomycin in water samples, with recoveries ranging from 80 to 120 %.
The positive effect of thiol compounds as reducing agents in the synthesis of gold nanoparticles (AuNPs) in the presence of a micellar medium of Triton X-100 (TX-100) has been photometrically studied using a reverse flow-injection system which operates in the stopped-flow mode (SF-rFIA) ( Figure A). The reaction of synthesis consists on the injection of tetrachloroauric acid (HAuCl 4 ) in a mixture of the thiol and the surfactant. The reaction plug is stopped in a thermostatic bath at 90 ºC during 4 minutes and then is translated to the photometer where the signal is measured at λ=540 nm. The analytical usefulness of this new system has been assessed by its application to the determination of thioglycolic acid (TGA), which was chosen as analyte model.Figures B and C depict the TEM images obtained for the mixture of HAuCl 4 and TGA in the absence and in the presence of TX-100 respectively. Figure B shows the formation of irregular polyhedral metallic clusters with a wide range of sizes, estimated between 60 and 300 nm. However the TEM image obtained in the presence of TGA and TX-100 shows the formation of spherical AuNPs with sizes in the range 10-40 nm.The formation of AuNPs increases in a linear mode with the concentration of TGA. The dynamic range of the calibration graph was 5.97 -80 µmol L -1 , and the detection limit was 1.73 µmol L -1 . Other thiol compounds (cysteine, N-acetylcysteine and homocysteine) and related compounds (methionine and homocystine) gave similar results, but gluthatione did not give any signal. The precision of the method, expressed as relative standard deviation, ranged between 1.5 and 2.3 %. The method was applied to the determination of TGA in several cosmetic samples with acceptable recoveries in all instances, which ranged between 90.32 and 101.46 %.
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