“…Since, MO is presented in the urine sample of patients and addicts at trace levels, a sensitive assay method is desirable. In order to improve the sensitivity of detection, high efficiency detectors such as mass spectrometry (MS) [9][10][11][12][13][14] and fluorescence [15][16][17] were applied. However, MS is an expensive technique, and fluorescence always needs critical derivatization reactions.…”