Lercanidipine

Reference substances of lercanidipine, telmisartan and valsartan were obtained from Sigma-Aldrich GmbH (Steinheim, Germany). Amlodipine and candesartan, as well as the deuterated internal standards (IS) diazepam-d₅, lorazepam-d₄ and nordiazepam-d₅ were purchased from LGC Standards GmbH (Wesel, Germany).
Acetonitrile was obtained from Karl Roth GmbH (Karlsruhe, Germany) and ethyl acetate from AppliChem (Darmstadt, Germany). Further chemicals and solvents used were supplied by Sigma-Aldrich GmbH (Steinheim, Germany). All reagents and solvents were either of analytical or LC grade.

Amlodipine besylate, barnidipine, bumetanide, doxazosin, hydrochlorothiazide, irbesartan, metoprolol, nifedipine, spironolactone, telmisartan, lercanidipine, and valsartan were purchased from Sigma-Aldrich Chemie (Zwijndrecht, Netherlands). Canrenone, doxazosin-d8, enalapril, enalapril-d5, hydrochlorothiazide-13Cd2, losartan, losartan-carboxylic acid, perindopril, and perindoprilat were purchased from Santa Cruz Biotechnology (Heidelberg, Germany). Enalaprilat and candesartan were purchased from Alfa Aesar (Kandel, Germany), and chlorthalidone was purchased from EDQM (Strasbourg, France) and Cayman (Ann Arbor, MI).
Acetonitrile [99.9%, high performance liquid chromatography (HPLC)-R grade], absolute methanol [liquid chromatography/mass spectrometry (LC/MS) grade], and formic acid (FA) (99.9%, UHPLC/MS grade) were purchased from Biosolve (Valkenswaard, Netherlands). Ammonium hydroxide (AH) was purchased from Merck Millipore (Darmstadt, Germany). Deionized water was produced with a Milli-Q Advantage A10 purification system from Merck-Millipore (Darmstadt, Germany). Fresh human blood without AHDs was obtained from patients who provided consent to use the remnant material for other purposes.

Antihypertensive drugs: ramipril, lercanidipine, valsartan, hydrochlorothiazide, telmisartan, perindopril, and nebivolol were purchased from Sigma-Aldrich (St. Louis, MO, USA). The structures, physicochemical properties and drug classes (pharmacological properties) of investigated substances are presented in Table 5. Chromatographic glass plates, HPTLC silica gel 60 F254 and HPTLC diol F254 were supplied by Merck (Darmstadt, Germany). Acetonitrile and methanol (both MS purity) were purchased from Fisher Chemical (Waltham, MA, USA). Ethanol, toluene and formic acid (98–100%) LC-MS grades were supplied by Merck (Darmstadt, Germany). The ultra-pure water was obtained from the Millipore Direct-Q3-UV purification system (Merck, Darmstadt, Germany). The plasma samples (also a reference sample) were kindly provided by the Cardiology Clinic of the Independent Public Clinical Hospital No. 4 in Lublin (Lublin, Poland).