In-line coupled single drop liquid-liquid-liquid microextraction with capillary electrophoresis for determining fluoroquinolones in water samples.

A simple in-line single drop liquid-liquid-liquid microextraction (SD-LLLME) coupled with 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 sixfold for ciprofloxacin (CIP). The linear range were 20-400 µg/L for ENR and 60-400 µg/L for CIP. The detection limits were 10.1 µg/L and 55.3 µg/L 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%).

Determination of sulfonylureas in cereal samples with electrophoretic method using ionic liquid with dispersed carbon nanotubes as electrophoretic buffer.

A capillary electrophoresis method to determine four sulfonylureas in grain samples was developed using 10mM of 1-butyl-3-methyl imidazolium tetrafluoroborate (bminBF4) as electrophoretic buffer solution. 2mgL(-1) of Surfactant Coated-Single Wall-Carbon Nanotubes (SC-SWCNTs) was added to the buffer solution to improve the resolution. In this way, the separation of nicosulfuron, ethoxysulfuron, sulfometuron methyl and chlorsulfuron was carried out in 16min without using organic solvents. A clean up-preconcentration procedure was done prior to inject the sample into the CE instrument, in order to achieve the established maximum residue limits (MRLs). So, the detection limits (LODs) for each analytes were between 16.8 and 26.6µgkg(-1). The relative standard deviations (RSDs) were in the range 1.9-6.7%. A recovery study using the so-called matrix matched calibration demonstrates that no matrix interferences were found throughout the determination. The recovery percentages were ranged between 80% and 113%.

Micellar nanotubes dispersed electrokinetic chromatography for the simultaneous determination of antibiotics in bovine milk.

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.

A simple and fast method for chlorsulfuron and metsulfuron methyl determination in water samples using multiwalled carbon nanotubes (MWCNTs) and capillary electrophoresis.

A new method to determine metsulfuron methyl (MSM) and chlorsulfuron (CS) in different water samples was developed. It consists in a solid phase extraction (SPE) procedure using multiwalled carbon nanotubes (MWCNTs) as sorbent material in combination with capillary zone electrophoretic determination. To carry out the pre-concentration step, a simple flow injection system was developed and optimized. Thus, 250 µL of aqueous solution containing methanol 50% (v/v) and acetonitrile 2% (v/v) as eluent, 10 mL of sample and a flow rate of 1.15 mL min(-1) were selected. The CE variables also were optimized. A rapid determination and good resolution of two herbicides were obtained within 9 min using a simple electrophoretic buffer (50 mmol L(-1) sodium tetraborate with 3% of methanol, pH=9.0). Under the optimum conditions, the calibration curves were linear between 0.5 and 6 µg L(-1) for MSM and CS with R(2)=0.995 and 0.997, respectively. The repeatability of the proposed method, expressed as relative standard deviation (RSD), varied between 4.1% and 5.4% (n=10) and the detection limits for MSM and CS were 0.40 and 0.36 µg L(-1), respectively. Good results were achieved when the proposed method was applied to spiked real water samples. The recoveries percentages of the two analytes were over the range 86-108%.