High spatial-resolution MS imaging of longitudinal- and transverse- cross sections of drug-incorporated ha

Significance of the Topic

Human hair retains drugs over extended periods, making it a valuable matrix for reconstructing exposure timelines in forensic and clinical settings. Conventional LC and LC-MS methods lack spatial resolution and localization data, whereas high-resolution MS imaging reveals distribution patterns within hair microstructures.

Objectives and Overview

This study demonstrates the use of Shimadzu’s iMScope imaging mass microscope combined with the iMLayer matrix coating device to achieve spatial resolutions down to 5 µm. Using methoxyphenamine (MOP) as a model compound, both longitudinal and transverse cross sections of hair—administered to volunteers or soaked in drug solution—are imaged to compare dosing history and penetration profiles.

Methodology and Instrumentation

Sample Preparation:

• User’s hair: Volunteers ingested 50 mg MOP hydrochloride thrice daily in two 5-day courses separated by rest periods; hair was collected post-root.
• Soaked hair: Drug-free hair immersed in MOP solution; drug load quantified as 20–83 ng/mg by LC.
• Sectioning: Longitudinal slices via microtome fixed on ITO slides with conductive tape; transverse slices cryosectioned after CMC embedding.

Matrix Application and Imaging:

• Matrix: CHCA applied by iMLayer at 0.7 µm thickness for uniform, fine crystals.
• Mass spectrometer: iMScope TRIO (Q-TOF) in positive mode, m/z 100–185, MS/MS precursor m/z 180.1.
• Spatial resolution: Pitch settings of 5, 10, or 50 µm; laser diameter adjustable (approx. 5–50 µm); laser shots per pixel 50–100 at 1000 Hz.

Main Results and Discussion

Longitudinal Imaging (50 µm):
The user’s hair exhibited alternating drug-positive and drug-negative zones matching the intake/rest schedule. Soaked hair showed a continuous distribution along the shaft.

High-Resolution Imaging (10 µm):
Soaked hair displayed intense peripheral signals, whereas user’s hair signals were diffuse, indicating different incorporation pathways.

Transverse Imaging (10 and 5 µm):
Peripheral ring patterns of MOP were clear in soaked hair across serial sections, confirming reproducibility. The user’s hair lacked a distinct ring, reflecting in vivo incorporation dynamics.

Benefits and Practical Applications

• Chronological mapping of drug intake events within a single hair fiber.
• Ability to distinguish between surface contamination and incorporation through blood.
• Enhanced forensic toxicology and anti-doping analyses with spatial context.
• Potential for evaluating penetration of active ingredients in cosmetic and hair care research.

Future Trends and Applications

Advances may include automated 3D reconstruction of drug distributions, integration with machine-learning image analysis, standardization for legal admissibility, and extension to metabolites or other analytes. Coupling high-resolution MS imaging with complementary modalities (e.g., optical microscopy) will broaden analytical capabilities.

Conclusion

High spatial-resolution MS imaging using iMLayer and iMScope provides detailed visualization of drug distribution in hair cross sections, offering unique insights into exposure history and incorporation pathways. This reproducible method holds promise for forensic, clinical, and cosmetic applications.

Reference

Analytical Chemistry 2020, 92 (8), 5821–5829. Shimadzu Corporation Application News 01-00146-EN.