Optical Chemical Sensors for Pharmaceutical Analysis Using 1,4-Bis(1,3-benzoxazol-2-yl)benzene as Sensing Material

Abstract

Optical chemical sensors were prepared for the determination of ethacrynate, berberine, picric acid and picrolonic acid in aqueous solutions based on the fluorescence quenching of 1,4-bis(1,3-benzoxazol-2-yl)benzene (BBOB) in differently plasticized PVC membranes. The possible quenching mechanisms are discussed in detail. The fluorescence changes of the sensing membranes involve the formation of complexes between BBOB and the quenchers in question. The optimum pH ranges for the determination of ethacrynate and berberine are 4.0–10 and 8.0–11, respectively, whereas 1.0–2.0 and 0.90–2.3 mol l ^{- 1} H ₂ SO ₄ media are the best for picric acid and picrolonic acid, respectively. The complex compositions of BBOB with the four quenchers are all 1:1. The sensors respond linearly in the measuring ranges 8.00 × 10 ^{- 2} –1.00 × 10 ^{- 4} mol l ^{- 1} for ethacrynate, 6.76 × 10 ^{- 4} –1.62 × 10 ^{- 5} mol l ^{- 1} for berberine and picrolonic acid and 2.88 × 10 ^{- 4} –4.36 × 10 ^{- 6} mol l ^{- 1} for picric acid. The response times to reach a stable signal were less than 30 s. In addition to the high reproducibilities, the sensors can reversibly and selectively respond to the quenchers of interest. The proposed sensors were applied to the direct assay of ethacrynic acid and berberine hydrochloride in commercial tablets and the indirect assay of cinchonine and VB ₁ through quantitative precipitation with picric acid and picrolonic acid, respectively. The results were in good agreement with those obtained by pharmacopoeial and other methods.