A micellar electrokinetic chromatographic method has been developed to analyze biological (human serum, saliva and urine) and environmental samples (three different water samples) for letrozole (LE), fluoxetine and their main metabolites. For this purpose a 20 mM borate buffer (pH 9.5) containing 20 mM SDS and 12% v:v 2-propanol was used as the background electrolyte. The samples were hydrodynamically injected for 6 s, separated in a fused-silica capillary at 25 kV and 50 degrees C and detected at 230 nm. Under these conditions, the migration times for all the studied compounds ranged from 3.0 up to 8.0 min. Linearity ranges were determined as 125-1500 ng/mL, whereas detection limits were from 37 to 120 ng/mL in biological samples and a value of 6 ng/mL in water samples. According to the validation study, the developed method was proved to be accurate, precise, sensitive, specific, rugged and robust. This method was applied to the analysis of different biological fluids at clinical levels, including two urine samples from patients undergoing treatment with LE or fluoxetine, and also to environmental samples at potentially polluting level. Prior to the determination, the samples were purified and pre-concentrated by means of an extraction-preconcentration step with a C18 cartridge and by eluting the compounds with methanol.

A simple, rapid, and sensitive method has been proposed and validated to directly quantify letrozole (LE) and its metabolite, bis-4-cyanophenylmethanol (ME) in urine samples (without any additional treatment) by micellar electrokinetic capillary chromatography (MEKC). In an effort to improve the selectivity and sensitivity of the method, the chemical and instrumental parameters were optimized. The best conditions were: 70 mM borate buffer (pH 9.2) and 40 mM SDS as BGE, 25 kV and 20 degrees C as working voltage and temperature, respectively, with hydrodynamic injection for 6 s. The reliability of the proposed method was also proved by means of a validation procedure based on precision, accuracy, linearity, LOD (15 microg/L for both of them) and LOQ studies. Moreover, an innovatory experimental and statistical design approach, upon a Plackett-Burman fractional factorial model, which involves the simultaneous evaluation of the global robustness and ruggedness effects, was applied. As it has been already stated, the proposed method has been successfully used to directly quantify both compounds in human urine samples, without any additional treatment, but the previously reached LOD and LOQ values can be improved by applying an SPE preconcentration procedure, also developed and optimized by the authors in this work. Real determinations of these analytes in clinical urines of a patient under LE treatment were performed, too.

A new method for the determination of ciprofloxacin, the major metabolite of enrofloxacin, for concentrations between 20 and 200 ng/mL by means of matrix isopotential synchronous fluorescence spectrometry and derivative techniques is proposed. This new method is useful for the determination of compounds in samples with unknown background fluorescence, such as ciprofloxacin in whey, without the need of tedious preseparation. The determination was performed in an ethanol/water medium (20% v/v) at pH 4.8, provided by adding a sodium acetate/acetic acid buffer solution. Since enrofloxacin is widely used as an antibacterial agent in veterinary medicine, the method was successfully applied to the determination of its main metabolite in milk. An exhaustive statistical analysis has been developed to all calibration graphs. This treatment includes robust regression such as least median of squares, which also detects outliers and leverage points. The overall least-squares regression has been applied to find the more exact straight line that fits the experimental data. The error propagation has been considered to calculate the detection limit and the repeatability of the method.

Micellar electrokinetic chromatography (MEKC) was investigated for the simultaneous determination of letrozole, imipramine and their metabolites in human urine samples over a concentration range of therapeutic interest. Experimental parameters such as pH of the running electrolyte, sodium dodecylsulphate (SDS) concentration, borate concentration, voltage, etc were investigated. Under optimal conditions of 25 mM SDS, 15 mM borate buffer (pH 9.2), 15% 2-propanol, as background electrolyte; 28 kV and 40 °C, as voltage and cartridge temperature, respectively; resolution between the peaks was greater than 1.7. Before the determination, a solid phase extraction (SPE) procedure with a C18 cartridge was optimized. Good linearity, accuracy, precision, robustness and ruggedness were achieved and detection limits of 12.5 ng/mL for letrozole and its metabolite and 37.5 ng/mL, were obtained for imipramine and their metabolites. Real determinations of these analytes in two patient urines were carried out. Sensitivity achieved in this method is sufficient to perform kinetic studies in humans.

This work presents a multi-residue analytical method based on solid phase extraction (SPE) followed by high-performance liquid chromatographic (HPLC) with diode array (DAD) detection for the simultaneous determination of a group of pharmaceutical products that include ten antidepressants and three anticanceri- genic in environmental samples (water and soil). Baseline separation of the studied compounds was obtained on an ultrabase C18 (4.6 mm i.d. × 150 mm, 5 μm particle) column using acetonitrile:phosphate buffer pH 2.5 (35:65 v/v) as mobile phase with a flow rate of 1.5 mL/min. Different aspects including linearity, accuracy, precision and detection and quantification limits were examined in order to validate the proposed method. Detection limits between 1 and 50 ng/mL were obtained for all the target compounds. This method was ap- plied to the analysis of environmental samples as waters and soils of different precedence. Prior, the HPLC determination the samples were purified and enriched using SPE or liquid-liquid extraction (LLE) of the tar- get compounds