Simultaneous analysis of 1,2,3,4-tetrahydroisoquinolines by high-performance liquid chromatography using 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride as a fluorescent labeling reagent

A highly sensitive high-performance liquid chromatographic method for the simultaneous analysis of 1,2,3,4-tetrahydroisoquinolines (TIQs) in the rat brain was developed. 1,2,3,4-Tetrahydroisoquinoline (TIQ), 1-methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ) and 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1-BeTIQ) were derivatized with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride to produce fluorescent sulfonamides. The labeling reaction was carried out at 50 °C for 15 min at pH 8.5. The fluorescent derivatives were separated on a reversed-phase column by gradient elution using (A) water–(B) acetonitrile/methanol (55:45) at 55 °C and detected by fluorescence measurement at 318 nm (excitation) and 398 nm (emission). The detection limits (signal-to-noise ratio = 3) were 8–9 fmol per injection. The relative standard deviations (n = 6) of TIQs were 2.6–10.5% and the recoveries were 87.6, 101.8 and 75.2%, respectively. The concentrations of TIQ, 1-MeTIQ and 1-BeTIQ in normal rat brains (n = 6) were 0.7 ± 0.3 (0.10 ± 0.04), 3.4 ± 1.5 (0.50 ± 0.22) and 1.3 ± 1.8 pmol/g (0.30 ± 0.41 ng/g), respectively.