Liquid–liquid microextraction without phase separation in a multicommuted flow system for diltiazem determination in pharmaceuticals

Liquid–liquid microextraction without phase segmentation was implemented in a multicommuted flow system for determination of the anti-hypertensive diltiazem. The procedure was based on ion pair formation between the drug and the dye bromothymol blue at pH 3.5. The detection was performed without phase separation in a glass tube coupled to a fiber-optics spectrophotometer. The total volume of chloroform was reduced to 50 μL in comparison with 10 mL consumed in batch. A linear response was observed between 9 and 120 μmol L−1, with a detection limit of 0.9 μmol L−1 (99.7% confidence level). The coefficient of variation (n = 10), sampling rate and extraction efficiency were estimated as 0.6%, 78 determinations per hour and 61%, respectively. About 30 μg of bromothymol blue was consumed and the waste volume was 380 μL per determination. The results for pharmaceutical samples agreed with those obtained by the reference procedure at the 95% confidence level.