Decontamination Wash
Definition
A multi-solvent surface wash (typically dichloromethane, methanol and aqueous buffer) applied before digestion to strip externally deposited drug from the cuticle. The wash itself is retained and analysed separately so the analyst can compare internal versus external loading and rebut a passive-exposure defence.
- Solvents used
- Dichloromethane, methanol, and aqueous buffer, typically
- Timing
- Applied before digestion of the hair or nail sample
- Target
- Externally deposited drug on the cuticle surface
- Key feature
- Wash retained and analysed separately from the digest
- Forensic use
- Rebuts a passive-exposure defence by comparing internal vs external loading
Common questions
Why does the multi-solvent sequence matter rather than a single wash step?+
Different solvents dissolve different classes of surface contaminant, a non-polar solvent for oils and residues, a polar solvent for water-soluble deposits, so a single wash type would leave some external contamination behind and understate what was actually on the surface.
How does retaining the wash solvent help address a passive-exposure defence?+
If the wash solvent itself tests positive for the drug at a level proportionate to what is found internally, that pattern supports an external contamination explanation; if the internal digest is strongly positive while the wash is comparatively clean, that pattern is harder to explain by passive exposure alone.
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