Enantiomeric analysis of overlapped chromatographic profiles in the presence of interferences. Determination of ibuprofen in a pharmaceutical formulation containing homatropine.

In this work, we studied the combination of chemometric methods with chromatographic separations as a strategy applied to the analysis of enantiomers when complete enantioseparation is difficult or requires long analysis times and, in addition, the target signals have interference from the matrix. We present the determination of ibuprofen enantiomers in pharmaceutical formulations containing homatropine as interference by chiral HPLC-DAD detection in combination with partial least-squares algorithms. The method has been applied to samples containing enantiomeric ratios from 95:5 to 99.5:0.5 and coelution of interferents. The results were validated using univariate calibration and without homatropine. Relative error of the method was less than 4.0%, for both enantiomers. Limits of detection (LOD) and quantification (LOQ) for (S)-(+)-ibuprofen were 4.96×10-10 and 1.50×10-9mol, respectively. LOD and LOQ for the R-(-)-ibuprofen were LOD=1.60×10-11mol and LOQ=4.85×10-11mol, respectively. Finally, the chemometric method was applied to the determination of enantiomeric purity of commercial pharmaceuticals. The ultimate goal of this research was the development of rapid, reliable, and robust methods for assessing enantiomeric purity by conventional diode array detector assisted by chemometric tools.

Automatized sspKa measurements of dihydrogen phosphate and Tris(hydroxymethyl) aminomethane in acetonitrile/water mixtures from 20 to 60°C.

We measured pKa values of Tris(hydroxymethyl)aminomethane and dihydrogen phosphate; both are commonly used to prepare buffers for reverse-phase liquid chromatography (RPLC), in acetonitrile/water mixtures from 0% to 70% (v/v) (64.6% (w/w)) acetonitrile and at 20, 30, 40, 50, and 60°C. The procedure is based on potentiometric measurements of pH of buffer solutions of variable solvent compositions using a glass electrode and a novel automated system. The method consists in the controlled additions of small volumes of a thermostated solution from an automatic buret into another isothermal solution containing exactly the same buffer-component concentrations, but a different solvent composition. The continuous changes in the solvent composition induce changes in the potentials. Thus, only two sequences of additions are needed: increasing the amount of acetonitrile from pure water and decreasing the content of acetonitrile from 70% (v/v) (64.6% (w/w)). In the procedure with homemade apparatus, times for additions, stirring, homogenization, and data acquisition are entirely controlled by software programmed for this specific routine. This rapid, fully automated method was applied to acquire more than 40 potential data covering the whole composition range (at each temperature) in about two hours and allowed a systematic study of the effect of temperature and acetonitrile composition on acid-base equilibria of two widely used substances to control pH close to 7. The experimental pKa results were fitted to empirical functions between pKa and temperature and acetonitrile composition. These equations allowed predictions of pKa to estimate the pH of mixtures at any composition and temperature, which would be very useful, for instance, during chromatographic method development.

Development of an ionic liquid-based dispersive liquid-liquid microextraction method for the determination of nifurtimox and benznidazole in human plasma.

Dispersive ionic liquid-liquid microextraction combined with liquid chromatography and UV detection was used for the determination of two antichagasic drugs in human plasma: nifurtimox and benznidazole. The effects of experimental parameters on extraction efficiency-the type and volume of ionic liquid and disperser solvent, pH, nature and concentration of salt, and the time for centrifugation and extraction-were investigated and optimized. Matrix effects were detected and thus the standard addition method was used for quantification. This microextraction procedure yielded significant improvements over those previously reported in the literature and has several advantages, including high inter-day reproducibility (relative standard deviation=1.02% and 3.66% for nifurtimox and benznidazole, respectively), extremely low detection limits (15.7 ng mL(-1) and 26.5 ng mL(-1) for nifurtimox and benznidazole, respectively), and minimal amounts of sample and extraction solvent required. Recoveries were high (98.0% and 79.8% for nifurtimox and benznidazole, respectively). The proposed methodology offers the advantage of highly satisfactory performance in addition to being inexpensive, simple, and fast in the extraction and preconcentration of these antichagasic drugs from human-plasma samples, with these characteristics being consistent with the practicability requirements in current clinical research or within the context of therapeutic monitoring.