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Detection of a GC/MS artifact peak as methamphetamine
C L Hornbeck1, J E Carrig, R J Czarny
1Navy Drug Screening Laboratory, San Diego, CA 92134-6900.
Journal of Analytical Toxicology
|September 1, 1993
Summary
High levels of pseudoephedrine or ephedrine in urine can create a false positive methamphetamine result using certain derivatization methods. This artifact peak is identified using GC/MS analysis, distinguishing it from actual methamphetamine.
Area of Science:
- Forensic Chemistry
- Analytical Chemistry
- Toxicology
Background:
- Laboratories have reported methamphetamine detection in negative urine samples.
- This phenomenon may stem from analytical interferences during drug testing.
Purpose of the Study:
- To investigate the cause of artifact peaks mimicking methamphetamine in urine specimens.
- To identify the source of these false positives and develop differentiation methods.
Main Methods:
- Gas chromatography-mass spectrometry (GC/MS) with selected ion monitoring (SIM) and full-scan analysis.
- Derivatization of urine specimens using 4-carbethoxyhexafluorobutyryl chloride (CB), heptafluorobutyric anhydride (HFB), and N-trifluoroacetyl-l-prolyl chloride (TFAP).
- Analysis of spiked samples with deuterated pseudoephedrine (PS) and ephedrine (EP) at high concentrations.
Main Results:
- An artifact peak, matching methamphetamine criteria, was observed in negative urine specimens containing high levels of PS or EP.
- This artifact is caused by thermal transformation of PS/EP in the GC injector during derivatization.
- GC/MS analysis confirmed that specimens with high PS/EP concentrations can yield false positives with immunoassay methods while testing negative by GC/MS.
- SIM analysis of CB derivatives can differentiate between PS and EP based on derivatization patterns.
Conclusions:
- Pseudoephedrine and ephedrine can cause false positive methamphetamine results in urine drug screens.
- GC/MS, particularly with full-scan and SIM analysis of derivatized compounds, is crucial for accurate methamphetamine identification and differentiation from interfering substances.