SPECTROPHOTOMETRIC DETERMINATION OF ENALAPRIL THROUGH TERNARY COMPLEX FORMATION

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 divided by 500 mu g/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 divided by 500 mu g/ml (correlation coefficient r = 0.9993). Limit of detection (LD) was 9.907 mu g/ml and limit of quantification (LQ) 33.024 mu g/ml. Precision showed an RSD = 1.83%, and accuracy with mean recovery is 102.6 % in the range 98.8 divided by 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.