Enalapril is an angiotensin-converting enzyme inhibitor widely used in the treatment of hypertension and heart failure.
Aim: To design and validate a simple and sensitive spectrophotometric method. This method is based on a ternary complex formation between enalapril, copper (II), and bromothymol blue, in a slightly alkaline environment, complex that is extractable in chloroform, with an absorption maximum at 426 nm.
Materials and methods: To a volume of 1 milliliter of standard enalapril drug solution in concentration range 200/500 microg/ml, two milliliters of Cu (II) chloride solution 0.2 % followed by 2 ml bromothymol blue solution 0.01% and 0.5 ml of pH 8 buffer solution (Britton-Robinson) were added. The complex was two times extracted with 2 x 1.5 ml chloroform. Ten minutes after extraction, absorbance was measured at 426 nm against blank.
Results: Our spectrophotometric method was validated by determining linearity, limit of detection and quantification, system and method precision, and method accuracy. The method showed a good linearity in the range 200/500 microg/ml (correlation coefficient r = 0.9993). Limit of detection (LD) was 9.907 microg/ml and limit of quantification (LQ) 33.024 microg/ml. Precision showed an RSD = 1.83%, and accuracy with mean recovery is 102.6% in the range 98.8/103.9.
Conclusions: The ternary complex formed under the above-mentioned condition and measured spectrophotometrically can be regarded as an ion-association complex between the metal-drug cation and bromothymol blue anion. The experimental results demonstrated a good sensitivity.