Boron nitride nanotubes for extraction of angiotensin receptor blockers from human plasma

The limitations of silica-based sorbents boosted the development of new extraction phases. In this study, boron nitride nanotubes functionalized with octadecyl groups were used for the first time as sorbent for extraction of losartan and valsartan, the most used angiotensin receptor blockers in the clinical practice, from human plasma. The nanotubes were synthesized using the chemical vapor deposition technique, purified by acid treatment, functionalized with octadecylamine in a microwave reactor, and characterized by different techniques. The functionalized nanotubes were packed in solid phase extraction cartridges. Extraction conditions were optimized by means of a 2³ factorial design with center points. The separation was performed on a biphenyl core-shell (100 × 4.6 mm; 2.6 µm) column, using 0.1 % (v/v) triethylamine solution and methanol (pH 3.2) as mobile phase, at 0.7 mL/min, in gradient elution. The injection volume was 10 µL and fluorescence detection was performed at excitation and emission wavelengths of 250 and 375 nm, respectively. The developed method was validated according to Brazilian Health Regulatory Agency (ANVISA), United States Food and Drug Administration (US FDA) and European Medicines Agency (EMA) guidelines and presented selectivity, precision, accuracy, and linearity in the concentration ranges of 50-1200 ng/mL for losartan and 20-1700 ng/mL for valsartan. Recoveries higher than 80 % were obtained. The method was fit for the quantification of losartan in plasma samples from patients under antihypertensive therapy, being useful in therapeutic drug monitoring, pharmacokinetics and bioequivalence studies.