Reversed-Phase HPLC
Definition
HPLC using a non-polar C18 stationary phase and a polar aqueous-organic mobile phase; components elute in order of increasing hydrophobicity; the standard mode for separating ink dye mixtures.
- Stationary phase
- Non-polar C18
- Mobile phase
- Polar aqueous-organic mixture
- Elution order
- Increasing hydrophobicity
- Forensic use
- Standard mode for ink dye mixture separation
Common questions
Why is reversed-phase HPLC preferred for ink dye separation over TLC alone?+
HPLC gives quantitative peak areas and better resolution of closely related dye components than TLC, and it can be coupled to a diode-array or mass spectrometric detector for a confirmatory spectral match rather than relying on spot colour and position alone.
How do examiners compare a questioned ink's HPLC profile to a reference?+
They compare retention times and relative peak areas of the separated dye components against ink standard reference collections or exemplar samples run under the same method, looking for a consistent dye formulation match.
Can reversed-phase HPLC alone date when an ink was written?+
No, dye separation identifies the ink formulation for comparison purposes, but dating relies on separate methods that track solvent loss or specific dye ageing markers over time, not on the chromatographic separation itself.
Related terms
- ATR-FTIR (Attenuated Total Reflectance FTIR)
- An FTIR sampling mode in which infrared light undergoes total internal reflection in a crystal pressed against the sample surface, probing only...
- D Band and G Band (Raman)
- The characteristic Raman bands of graphitic carbon materials at approximately 1350 cm-1 (D, disorder) and 1590 cm-1 (G, graphitic C-C stretch); diagnostic...
- ENFSI FIDE-WG
- The European Network of Forensic Science Institutes Forensic Document Examination Working Group, which publishes best-practice manuals for document examination methods including ink...
- ESI-MS (Electrospray Ionisation Mass Spectrometry)
- An ionisation technique for LC-MS coupling that gently ionises analytes from solution at atmospheric pressure; produces molecular ion clusters and charge-state distributions...
- Photodiode-Array (PDA) Detector
- An HPLC detector that records a full UV-Vis absorption spectrum at every elution time point, producing a 3D data matrix (time, wavelength,...
- Rf Value (Retardation Factor)
- In TLC, the ratio of the distance migrated by a component to the distance migrated by the solvent front; a characteristic value...
- Solvent-Loss Dating
- An ink dating approach based on measuring the concentration of residual semi-volatile solvents (particularly phenoxyethanol in ballpoint ink) relative to a non-volatile...
- SWGMAT Guidelines
- Guidelines issued by the Scientific Working Group for Materials Analysis (US), which define best practices for forensic ink analysis including method validation,...
- Video Spectral Comparator (VSC)
- A multispectral imaging instrument combining UV, visible, and near-infrared illumination with selectable emission filters and a calibrated digital camera; the primary bench...