VALIDATION FOR QUANTITATIVE OF METHADONE ENANTIOMERS AND ITS MAJOR METABOLITE USING VANCOMYCIN COLUMN COUPLED WITH MASS SPECTROMETRIC DETECTION AND ITS APPLICATION TO CLINICAL SAMPLES Journal title: International Journal of Pharmacy and Pharmaceutical Sciences Authors: Nurfadhlina Musa, Sim Hann Liang, Tan Soo Choon, Rusli Ismail Subject(s):