Compatibility of highly sulfated cyclodextrin with electrospray ionization at low nanoliter/minute flow rates and its application to capillary electrophoresis/electrospray ionization mass spectrometric analysis of cathinone derivatives and their optical i

Abstract

RATIONALE: Sodium salts of cyclodextrins are commonly used in capillary electrophoresis/mass spectrometry (CE/MS) analysis of illicit drugs and their optical isomers. To avoid the suppression effect of cyclodextrins under electrospray ionization (ESI), the partial filling technique (PFT) is commonly utilized, which has a limited resolution. Low-flow nano-ESI has been shown to reduce the suppression effect of the salts. To test the compatibility of low-flow ESI with a background electrolyte (BGE) containing sodium salts of cyclodextrin, sheathless narrow capillary CE/MS with flow rates of low nanoliters/minute (nL/min) was applied to the separation and detection of cathinones and their positional and optical isomers for the first time. METHODS: Low-flow sheathless CE/MS using a 20-μm-i.d. capillary in conjunction with a porous tip interface was used for the separation of cathinone derivatives and their optical isomers. Highly sulfated γ-cyclodextrin (HS-γ-CD) in conjunction with (+)-18-crown-6-tetracarboxylic acid ((+)-18-C-6-TCA) was used as the BGE and an ion trap mass spectrometer operating in full scan mode was utilized. RESULTS: Utilizing low flow rate (~10 nL/min) sheathless CE/MS, the use of the sodium salt of HS-γ-CD as the BGE was compared with the same solution using PFT. The relative and absolute sensitivity of detection of cathinones were about the same, indicating that under low-flow sheathless CE/MS there was no significant suppression due to the existence of HS-γ-CD in the electrospray process. However, enhanced resolution of cathinone derivatives and their positional and optical isomers was observed when the solution of HS-γ-CD was used as the BGE. The enhanced resolution was because of the presence of the HS-γ-CD in the entire capillary during the analysis. The addition of 15 mM (+)-18-C-6-TCA to the BGE containing HS-γ-CD further enhanced the resolution resulting in separation of all cathinones and their positional and optical isomers. CONCLUSIONS: A novel CE/MS technique has been introduced that combines low-flow sheathless CE/MS, with HS-γ-CD and 15 mM (+)-18-C-6-TCA as the BGE for separation of cathinone derivatives as well as their positional and optical isomers.

Improving the sensitivity in chiral capillary electrophoresis

“…For instance, a recent article published by Moini et al. described the application of a low‐flow sheathless nanospray interface on the enantioseparation of illicit drugs by means of the highly sulfated‐γ‐CD. In conventional sheath interfaces, high ion suppression would be expected when using this chiral selector.…”

Ultrafast capillary electrophoresis/mass spectrometry of controlled substances with optical isomer separation in about a minute

“…Under the experimental conditions used here, methamphetamine isomers, secondary amines, were not separated using (+)‐18‐C‐6‐TCA. It is possible that using another chiral selector, such as a cyclodextrin, would enable the separation of the methamphetamine isomers …”

“…In forensic toxicology, CE has been used for the identification of drugs and their metabolites in various body fluids . One advantage of CE is that it allows for the separation of a wide range of compounds usually by simply changing the background electrolyte . Like LC, CE does not require derivatization of analytes and the thermal stability of the compounds is not an issue.…”

Recent advances in CE‐MS coupling: Instrumentation, methodology, and applications

“…This construction is based on 30 μm id emitter constructed from porous glass membrane surrounded by a conductive liquid, providing electrical connection without any noticeable sample dilution. In the pursuit of a stable electrospray at low flow rates, better ionization efficiency and resolution power, Moini investigated possibilities of the instrumentation based on porous emitter with id of 5–20 μm in the applications mentioned elsewhere in this review . Recently, Guo et al.…”