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DART Mass Spectrometry of Writing Inks

Midwest Forensics Resource Center. DART Mass Spectrometry of Writing Inks. Roger Jones Midwest Forensics Resource Center and Ames Laboratory—USDOE, Iowa State University. DART MS of Writing Inks. Comparison to Conventional Ink Analysis Spectrum Acquisition Presentation of Sample

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DART Mass Spectrometry of Writing Inks

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  1. Midwest Forensics Resource Center DART Mass Spectrometry of Writing Inks Roger Jones Midwest Forensics Resource Center and Ames Laboratory—USDOE, Iowa State University

  2. DART MS of Writing Inks • Comparison to Conventional Ink Analysis • Spectrum Acquisition • Presentation of Sample • Instrumental Conditions and Data Acquisition • NIST Mass Spectral Search Program • Interference from Paper • Effects of Writing Age • Identification of Ink Components • Ink Identification Using NIST Software

  3. Comparison to Conventional Methods • Optical Inspection • Side-by-side comparison under various illuminations through various filters • Strengths: Quick, cheap, non-destructive, often sufficient • Weaknesses: Requires physical reference, provides minimal information, no library possible, cannot identify ink

  4. Comparison to Conventional Methods • Thin Layer Chromatography • Side-by-side comparison, separates and detects dyes and fluorescent components • Strengths: Cheap, usually sufficient, more information than optical inspection, can build library, may identify ink • Weaknesses: Slow, destructive, requires physical reference, sensitive to environment, less information than DART, requires physical sample library

  5. Comparison to Conventional Methods • DART MS • Elemental formula determination of all volatile and semi-volatile components • Strengths: Quick, non-destructive, no physical reference, provides lots of information, database library, can identify ink, complementary to dye-sensitive methods • Weaknesses: Expensive equipment, sensitive to vehicle, paper occasionally interferes

  6. MS of Extracts vs. DART MS in Situ DART MS of Ink on Paper ESI-MS of Extracts 5 Black Bic Ballpoints

  7. Presentation of Sample Modified Wikipedia image, with acknowledgement to JEOL USA, Inc., and author R. B. Cody

  8. Full Page in Open Sample Holder

  9. Full Page in Open Sample Holder

  10. Sample Held by Cover-Plate Hook 1/8-inch hole in cover plate gives access to sample.

  11. Page in Closed Sample Holder

  12. Sample in Position for Analysis

  13. Instrumental Conditions Mount wired to spectrometer inlet –3500 V +150 V 3.25 L/min He 255 °C +650 V +20 V, 80 °C Modified Wikipedia image, with acknowledgement to JEOL USA, Inc., and author R. B. Cody

  14. Raw Spectra from Chromatogram Zebra Rubber 80 Ballpoint on Hammermill Fore DP Paper 30 second averages

  15. Final Spectrum from Raw Spectra Zebra Rubber 80 Ballpoint on Hammermill Fore DP Paper

  16. DART MS of 3 Main Ink Types

  17. NIST Spectral Search Software • NIST Mass Spectral Search Program • Demo Version 2.0d is a free download. • Fully functional software with a small library • Search Types • Spectral match; reverse/forward, with m/z limits, identity/similarity, match ring number • Search formula, name, CAS number, NIST registry number, peaks • Constraints; molecular weight, elemental abundance, peak presence

  18. NIST Spectrum Search Results Comparing unknown and highlighted match Distribution of matches Unknown Spectrum of unknown Spectrum of highlighted match List of matches

  19. Calculating Match Quality Match Quality, Q, combines two factors, F1 and F2, that range from 0 to 1. F1 is a mass-weighted dot product of the two spectra: Sums are over M; M = m/z AL = relative intensity of library peak AU = relative intensity of unknown peak From Stein, J. Am. Soc. Mass Spec., 1994, 5, 316.

  20. Calculating Match Quality F2 compares ratios of successive peaks: NU&L = number of peaks common to both unknown and library spectra. Sum is over those peaks. n = 1 if AL ratio < AU ratio, n = -1 if AU ratio < AL ratio. Q is 999 for a perfect match.

  21. Test of Paper Effects • Lines written freehand on 16 different types of paper with three pens—1 ballpoint, 1 gel, 1 fluid ink. • Stored in closed file in drawer for 8–9 months. • Three spectra acquired for each ink on each paper. Samples handled with gloves. • All spectra for one ink placed in a NIST library. • All spectra searched against the library and match qualities determined for each spectrum. Reverse matching with no m/z limit.

  22. Papers Used in Test

  23. Ballpoint Spectrum Match Qualities Distribution of Match Qualities of One Spectrum with 45 Spectra of the Same Ink on Different Paper: Black Zebra Rubber 80 Ballpoint Ink on Hammermill Fore Median Match Quality = 880

  24. Spectra Matching a Ballpoint Spectrum Spectral Matching for a sample of Zebra Rubber 80 Black Ballpoint on Hammermill Fore DP Paper

  25. Median Match Qualities for Ballpoint Distribution of Median Match Qualities with 45 Spectra of the Same Ink on Different Paper: Black Zebra Rubber 80 Ballpoint Ink

  26. Gel Ink Spectrum Match Qualities Distribution of Match Qualities of One Spectrum with 45 Spectra of the Same Ink on Different Paper: Black Bic Cristal Gel Roller Ink on Hammermill Fore DP Median Match Quality = 854

  27. Median Match Qualities for Gel Ink Distribution of Median Match Qualities with 45 Spectra of the Same Ink on Different Paper: Black Bic Cristal Gel Roller Ink

  28. Fluid Ink Spectrum Match Qualities Distribution of Match Qualities of One Spectrum with 45 Spectra of the Same Ink on Different Paper: Blue Mont Blanc Le Grand Roller Ink on Hammermill Fore Median Match Quality = 777

  29. Median Match Qualities for Fluid Ink Distribution of Median Match Qualities with 45 Spectra of the Same Ink on Different Paper: Blue Mont Blanc Le Grand Rollerball Ink

  30. Effects of Writing Age • Lines written freehand periodically on white copy paper (Hammermill Fore DP). • Stored in closed folder in desk drawer with blank pages surrounding each written page. • Samples handled with gloves during analysis. • Three spectra at each age averaged for time plots.

  31. Black Bic Round Stic Ballpoint at Two Ages

  32. Components of Bic Ballpoint

  33. Crystal Violet Cationic Dye

  34. Crystal Violet DART Spectrum

  35. Aging of Black Bic Round Stic Ballpoint

  36. Black Bic Cristal Gel Roller Ink at Two Ages

  37. Components of Bic Gel Ink

  38. Aging of Black Bic Cristal Gel Roller Ink

  39. BlueMont Blanc Le Grand Rollerball Fluid Ink at Two Ages

  40. BlueMont Blanc Le Grand Rollerball Fluid Ink at Two Ages

  41. Components of Mont Blanc Ink

  42. Aging of Blue Mont BlancLe Grand Rollerball Fluid Ink

  43. Ink Identification • Library of 166 inks: 76 ballpoints, 50 fluid inks and 40 gel inks. • Written 10 to 35 months before testing. • 2 spectra of each ink placed in NIST library for the correct ink type. Handled with gloves. • Every spectrum tested as an unknown. • Perfect match with self is ignored, so Hit #1 is next best match • Ink correctly identified if Hit #1 is the other spectrum for the same ink.

  44. Ink Identification Test Results

  45. Unknowns that Matched Incorrectly • Black Ballpoints – 1 error • PaperMate Flexgrip Elite matched Papermate Flexgrip Ultra • Blue Ballpoints – 0 errors • Black Gels – 3 errors • 2 Pentel Sunburst Gels matched a Parker Gel Refill and an Integra Roller Gel • Zebra Jell 3 matched Parker Gel Refill • Blue Gels – 1 error • Pentel Hybrid H2 matched Pentel Sunburst Gel

  46. Unknowns that Matched Incorrectly • Black Fluids – 10 errors • Blue Fluids – 11 errors

  47. Match Quality of Correct and Closest Incorrect Matches for Black Ballpoints

  48. Match Quality of Correct and Closest Incorrect Matches for Blue Ballpoints

  49. Match Quality of Correct and Closest Incorrect Matches for Black Gel Inks Pentel Sunburst

  50. Match Quality of Correct and Closest Incorrect Matches for Black Fluid Inks

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