Determinação de losartana e valsartana em plasma humano empregando extração em fase sólida à base de nanotubos de nitreto de boro e cromatografia a líquido de alta eficiência.

Abstract

The determination of drugs in biological fluids can be done for different purposes. However, the complexity of these matrices can make the sample preparation step challenging. Solid phase extraction has been one of the main techniques for extracting molecules from the most diverse types of liquid samples. Despite the advances achieved with the development of several miniaturized solid phase extraction devices, the main sorbents used are based on organosilane reagents, chemically bonded to the silica surface. Due to the inherent limitations of these sorbents, the development of new extracting phases has become a viable alternative to improve the technique. In the present study, losartan and valsartan were determined in human plasma, the two drugs of the class of angiotensin II receptor antagonists most used in clinical practice. These drugs were extracted in cartridges for solid phase extraction, containing boron nitride nanotubes functionalized with octadecyl groups as sorbent, and analyzed by high-performance liquid chromatography coupled with a fluorescence detector. The optimized extraction conditions, obtained through factorial design, were 60 mg of nanosorbent; 2 mL methanol for solid phase activation; 500 µL of potassium phosphate monobasic anhydrous buffer 10 mM pH 2 for cartridge conditioning; flow rate of approximately 0.3 mL/min for the passage of samples; 250 µL of a mixture of potassium phosphate monobasic anhydrous buffer 10 mM pH 2 and methanol (90:10) for the wash step; and 2 mL of methanol for drug elution. Between one extraction and another, 1 mL of acetonitrile was passed through the cartridges to remove interfering compounds strongly retained by the nanosorbent. Irbesartan was used as an internal standard. The chromatographic conditions of the bioanalytical method allowed the separation of compounds of interest and interfering compounds with satisfactory resolution and running time. The chromatographic conditions used were: core-shell biphenyl analytical column (100 x 4.6 mm; 2.6 µm); mobile phase composed of 0.1% (v/v) triethylamine and methanol (pH 3.2), in gradient elution, at 0.7 mL/min; injection volume of 10 µL; temperature 25 ± 3 °C; and 250 nm excitation and 375 nm emission wavelengths. The evaluation of the figures of merit, according to the recommendations of the national and international validation guidelines, made it possible to observe linearity, precision and accuracy, in the concentration ranges of 50 – 1200 ng/mL for losartan and 20 – 1700 ng/mL for valsartan. The applicability of the method was confirmed through the analysis of plasma samples from patients undergoing antihypertensive therapy.