Working standards of CDS and HCTZ were provided by EDGM (Company identification: European Directorate
for the Quality of Medicines & Healthcare). Medical drugs—tablets containing 12.5 mg HCTZ and 16 mg CDS
drug Atakand Plus (Astra Zeneka AB, Sweden). HPLC: acetonitrile was purchased from the firm SPC “Cryochrom”,
ethylacetate CP (chemically pure) and formic acid PFA (pure for analyses). All reagents were used without
further purification. Blank human plasma was obtained from the blood bank and stored at −20˚C prior to use.
Water was purified using a Milli-Q reagent Grade Water System.