QUANTITATIVE CAPILLARY ELECTROPHORESIS ION SPRAY MASS-SPECTROMETRY ON A BENCHTOP ION-TRAP FOR THE DETERMINATION OF ISOQUINOLINE ALKALOIDS

The quantitative determination of some isoquinoline alkaloid natural products is described using combined capillary electrophoresis-ion trap mass spectrometry (CE/MS). The benchtop ion trap is a previously described modified commercial Varian Saturn II system equipped with an in-house constructed atmospheric pressure ionzation (API) ion source which was operated in the ion spray CE/MS mode. Ah relevant operational parameters have been optimized for the CE/MS experiments described in this work. A coaxial sheath now of solvent buffer was used to facilitate ion spray CE/MS operation. Analysis of synthetic mixtures containing nine related isoquinoline alkaloids provided full-scan mass spectra for these compounds with injected quantities as low as 370 attomole. The signal-to-noise ratio was better than 10/1 for the extracted ion current electropherograms of the parent ions for these compounds with injected quantities in the 370-510 attomole range. CE/MS analysis of methanol extracts from the natural bark of Phellodendron wilsonii as well as an herbal medication provided full-scan mass spectra for the identification of major and minor components in the mixture. Quantitative analyses were carried out using tetrahydroberberine as an internal standard. The standard curve ranged from injected levels of 0.6 to 16 pg (1.7 to 45 fmol) and had correlation coefficients of 0.998 and 0.999 for berberine and palmatine, respectively. These results suggest that the ion trap CE/MS system is sufficiently sensitive and reliable to provide acceptable quantitative analysis of synthetic and natural product mixtures.