A simple high pH liquid chromatography-tandem mass spectrometry method for basic compounds: application to ephedrines
Nicola Gray1, Alessandro Musenga, David A Cowan
1Department of Forensic Science & Drug Monitoring, Pharmaceutical Science Division, King's College London, London SE1 9NH, UK.
Journal of Chromatography. A
|November 25, 2010
Summary
Developing accurate doping control methods requires careful selection of liquid chromatography-mass spectrometry (LC-MS) conditions. This study found that atmospheric pressure chemical ionization (APCI) offers superior stability and reproducibility for analyzing ephedrines compared to electrospray ionization (ESI).
Area of Science:
- Analytical Chemistry
- Forensic Science
- Biochemistry
Background:
- Liquid chromatography-mass spectrometry (LC-MS) is crucial for doping control.
- Analyzing hydrophilic, basic compounds like ephedrines presents chromatographic and detection challenges.
- High pH mobile phases improve separation but can negatively impact MS detection.
Purpose of the Study:
- To develop and optimize an LC-MS/MS method for ephedrine analysis in doping control.
- To evaluate the performance of different ionization sources (ESI vs. APCI) with high pH mobile phases.
- To ensure accurate quantification of ephedrines without compromising chromatographic separation.
Main Methods:
- Reversed-phase LC with high pH mobile phase for ephedrine separation.
- Comparison of Electrospray Ionization (ESI) and Atmospheric Pressure Chemical Ionization (APCI) as ion sources.
- LC-MS/MS analysis of pseudoephedrine in urine samples (25-400 μg/mL) after simple dilution.
Main Results:
- High pH mobile phase improved ephedrine separation, reducing peak tailing and enhancing retention.
- ESI resulted in non-linear and poorly reproducible signals with the high pH mobile phase.
- APCI provided significantly greater stability and reproducibility compared to ESI.
- Errors for pseudoephedrine analysis were reduced from 49.3% (ESI) to 15.4% (APCI).
Conclusions:
- APCI is a more suitable ion source than ESI for analyzing basic compounds like ephedrines using high pH mobile phases in LC-MS.
- Optimizing MS conditions is critical for stable and accurate quantification in doping control.
- Method development requires balancing chromatographic performance with mass spectrometric detection.
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