REVERSED-PHASE ION-PAIR CHROMATOGRAPHIC ANALYSIS OF TETRACYCLINE ANTIBIOTICS - APPLICATION TO DISCOLORED TEETH

A high-performance liquid chromatographic method with diode array dete ction was developed to simultaneously separate tetracycline antibiotic s and applied to the analysis of discolored teeth. By a reversed-phase ion-pair chromatographic system using pentanesulfonate as a counter i on, minocycline, oxytetracycline, tetracycline and demeclocycline were eluted in this order, and they showed base-line separation within 9 m in. When using oxytetracycline as an internal standard, the quantitati ve ranges were between 2.5 ng/ml and 7.5 mu g/ml. Powdered dentine (10 mg) and enamel (40 mg) prepared from discolored primary teeth were so nicated in 0.25 mi of 10 mM HCl containing oxytetracycline (0.75 mu g/ ml) and 50 mM EDTA-2Na, thereafter the supernatants were chromatograph ed. Eluates from both discolored tooth samples were identified as mino cycline based on diode array spectra of their peaks, while minocycline was not detected in any samples from nondiscolored normal teeth, indi cating that discoloration of the tested teeth was due to minocycline i ncorporated into dentine and enamel. Replicate quantitative analyses o f the identical tooth substances showed that intra-and inter-assay C.V .s were 2.63 and 4.95% for dentine, and 5.42 and 10.88% for enamel. Ap plication of the developed method to nine discolored teeth revealed th at the incorporated minocycline ranged from 20.13 to 84.62 ng/mg of de ntine and 0.89 to 7.87 ng/mg of enamel. (C) 1998 Elsevier Science B.V.