HPLC-DAD
Definition
High-performance liquid chromatography with diode-array detection. Separates ink dyes on a C18 column and records UV-visible spectra at each elution point, providing quantitative dye identification at nanogram levels. Governed by ASTM E2286.
- Full name
- High-performance liquid chromatography, diode-array detection
- Column type
- C18
- Standard
- ASTM E2286
- Sensitivity
- Quantitative dye identification at nanogram levels
Common questions
How does HPLC-DAD complement TLC in ink analysis?+
TLC is a fast screening step that separates dye components visually on a plate, while HPLC-DAD adds quantitative separation plus a full UV-visible spectrum at each elution point, giving a more precise chemical fingerprint that can distinguish inks TLC alone might class as similar.
Why is quantitative dye identification useful in a questioned document case?+
Two pens can appear visually identical yet contain different proportions of the same dyes, or the same dyes from different manufacturing batches, and quantitative HPLC-DAD data can detect those differences to support or exclude common source and to help date an entry if a formulation change is documented.
Does HPLC-DAD consume the ink sample being tested?+
Yes, it requires extracting ink from the document, typically via a small punch, which is destructive at that microscopic scale, so it is generally reserved for cases where non-destructive methods like the video spectral comparator have not resolved the question.
Related terms
- ASTM E2285 / E2286
- The two ASTM International standards governing forensic ink examination: E2285 covers TLC-based ink alteration examination; E2286 covers HPLC-based ink comparison. Both are...
- Ballpoint Ink
- An oil-based, high-viscosity ink using a resin binder (alkyd or polyamide) in a high-boiling solvent (phenoxyethanol or benzyl alcohol), with triphenylmethane dyes...
- Iron-Gall Ink
- A historical ink formulation of ferrous sulphate, tannic acid (from oak galls), and gum arabic. The ferrous-tannate complex oxidises to brown ferric-tannate...
- Phenoxyethanol
- The primary high-boiling solvent in most modern ballpoint ink formulations. Its progressive evaporation from the dried ink film after writing is the...
- Raman Microspectroscopy
- A vibrational spectroscopy technique using a focused laser beam to excite molecular vibrations in an ink sample. Non-destructive. Primary method for toner...
- TLC (Thin-Layer Chromatography)
- A planar chromatography technique on silica gel plates that separates ink dye mixtures by polarity. ASTM E2285 governs its forensic application. The...
- Toner
- A dry-powder printing material consisting of fine styrene-acrylate polymer particles carrying carbon black and organic pigment, electrostatically applied and thermally fused at...
- USSS International Ink Library
- A collection of ~10,000 dated writing ink formulations maintained by the United States Secret Service since 1968, providing a terminus post quem...
- VSC (Video Spectral Comparator)
- A multispectral imaging instrument used in document examination; illuminates the document at multiple wavelengths (UV, visible, near-IR, IR) and captures fluorescence and...