Determination of the optical purity of timolol maleate by proton nuclear magnetic resonance spectroscopy with a chiral Pr(III) shift reagent.

A 1H NMR spectroscopic method with chiral shift chelate is presented for the determination of the optical purity of timolol maleate. Optimum experimental conditions were established by studying the interactions of solvents (CCl4, CDCl3), substrate concentration, and the type and concentration of chiral lanthanide chelate (Pr(hfc)3, Eu(hfc)3). Larger induced shift (delta delta) and enantiomeric shift difference (delta delta delta) values, and more detailed spectral differences were obtained with Pr(hfc)3 than with Eu(hfc)3. By monitoring the spectral changes of the resonance signals for the enantiomeric -C(CH3)3 protons, suitable conditions for quantitative determinations were found when 0.1 molar equivalents of Pr(hfc)3 were complexed with 0.074 M of substrate. Enantiomeric compositions were calculated from the relative intensities of the enantiomeric -C(CH3)3 proton resonances. Based on the analysis of six synthetic enantiomeric mixtures, the mean +/- SD recovery of (R)-(+)-timolol by the proposed method was 99.5 +/- 1.17% of the amount added.