Guor Rong Her

Analysis of coptisine, berberine and palmatine in adulterated Chinese medicine by capillary electrophoresis-electrospray ion trap mass spectrometry.

Chinese medicine preparations contaminated with coptisine, berberine and palmatine were studied by capillary electrophoresis-electrospray ion trap mass spectrometry. The dubious adulterants were identified by their retention times, molecular ions and specific fragment ions produced from collision induced dissociation. The results showed that, in comparison with CE-UV and capillary electrophoresis-electrospray mass spectrometry (CE-ESI-MS), more reliable identification could be achieved with CE-ESI-MS-MS using ion trap mass spectrometry.

Determination of linkages of linear and branched oligosaccharides using closed-ring chromophore labeling and negative ion trap mass spectrometry

Linear as well as branched oligosaccharides were labeled with p-aminobenzoic ethyl ester (ABEE) using the glycosylamine closed-ring labeling approach and analyzed by negative-ion electrospray ionization mass spectrometry (ESI-MS). Linkage specific fragment ions of ABEE labeled linear oligosaccharides were proposed based on the MS2 and MS3 data for several ABEE labeled linear oligosaccharides with known linkage configurations. Fragmentation at the reducing end was similar to that observed for ABEE disaccharides whereas the fragmentation pattern not involving the reducing end was similar to underivatized disaccharides. Based on these ions, all the linkages of linear oligosaccharides could be unambiguously determined. The fragmentation pattern at the branched sugar was in general not quite the same as the linear one. However, many linkage specific fragment ions were also observed for linkages at the branched sugar. These ions along with the ions proposed for linear oligosaccharides were found to be quite useful for the determination of all the linkages of branched oligosaccharides.

On-line monitoring trihalomethanes in chlorinated water by membrane introduction–fast gas chromatography mass–spectrometry

An analytical method based on membrane introduction and fast gas chromatography-mass spectrometry (GC-MS) has been developed for the on-line monitoring of trihatomethanes (THMs) in chlorinated drinking water. The coupling of membrane introduction with fast GC-MS offers the advantage of membrane introduction as an on-line sampling device and fast GC-MS as a separation and identification method. While maintaining the on-line monitoring characteristic of traditional membrane introduction mass spectrometry (MIMS), the difficulty of distinguishing CHCl3 and CHBrCl2 in MIMS was overcome by rapid GC separation and MS analysis. Water permeated across the membrane affected the analysis of CHBr2Cl and CHBr3. A method based on controlling the injection temperature and injection time has been developed to overcome the moisture problem. This method is simple and less time consuming than the conventional moisture removing method. Under typical operating conditions, the sampling rate was about 20 samples h(-1) capable of on-line monitoring THMs in chlorinated drinking water. The detection limits of this system were found to be about 2 ppt, 4 ppt, 4 ppt, and 8 ppt for CHCl3 CHBrCl2, CHBr2Cl, and CHBr3, respectively.

System peaks of cyclodextrins in capillary electrophoresis

Using a running buffer containing cyclodextrins (CDs) and 2-[N-cyclohexylamino-ethanesulfonic acid (CHES), positive system peaks were observed in the analysis of a ganglioside mixture by CE-UV. These system peaks were related to CDs in the running buffer because these peaks were also detected when a plug of solution devoid of CDs but having the same CHES concentration and pH as the running buffer was injected. Neutral CDs were separated owing to the formation of inclusion complexes with the anionic CHES ion. One possible explanation for the positive system peaks is that the anionic CD-CHES inclusion complex is displaced by co-ions with higher UV absorptivity.

The development of a hydrodynamic flow assisted double junction interface for signal improvement in capillary electrophoresis-mass spectrometry using positively charged nonvolatile additives.

To alleviate signal suppression resulting from nonvolatile positive ion additives, a hydrodynamic flow assisted double junction capillary electrophoresis-mass spectrometry (CE-MS) interface was proposed. The double junction interface which could alleviate the ion suppression due to nonvolatile negative ion additives was modified so that a hydrodynamic flow could be introduced to the interface. Using this setup, the apparent velocity of the ions was determined based on its electrophoretic mobility, electroosmotic flow in the transfer capillary, and hydrodynamic flow introduced by the syringe pump. CE-MS analysis of positively charged triazines was performed to demonstrate the practical value of this approach by using cetyltrimethylammonium ion (CTA(+)) as an additive. Because the separation column was dynamically coated with CTA(+), the EOF was reversed and the separation was performed under counter EOF mode. Under an appropriate hydrodynamic flow, the analytes (triazines) could be propagated toward the MS, whereas the additive (CTA(+)) ion was retained in the interface. Consequently, the problem of signal suppression by CTA(+) was alleviated, and the signals were enhanced more than 20-fold.