DETERMINATION OF (-)-BUNOLOL AND ITS METABOLITE, DIHYDRO-(-)-BUNOLOL, IN HUMAN AQUEOUS-HUMOR BY GAS-CHROMATOGRAPHY NEGATIVE-ION CHEMICAL IONIZATION MASS-SPECTROMETRY

(-)-Bunolol (LB) was applied to the human eye in a commercially available eye drop formulation. LB and its metabolite, dihydro-(-)-bunolol (DHLB) were identified and quantified in human aqueous humour. The compounds were analysed as their trimethylsilyl-pentafluorobenzamide derivatives using gas chromatography-negative ion chemical ionisation mass spectrometry. In the case of DHLB the corresponding H-2(3)-labelled isotopomers were used as internal standards and LB was quantified against its methoxime derivative. Calibration curves for LB and DHLB against internal standards were linear with correlation coefficients 0.994 and 0.996, respectively. Replicate analyses of a pooled sample of aqueous humour containing LB and DHLB gave standard errors of the mean of +/- 9.8 and +/- 2.4% for the concentrations of LB and DHLB, respectively. The practical limit of detection of the method was ca. 30 pg for LB and ca. 100 pg for DHLB. The derivatization procedure was also satisfactory for the analysis of a number of other beta-blockers which are used in ophthalmological practice.