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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

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
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
comparison to conventional methods
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
comparison to conventional methods4
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
comparison to conventional methods5
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
ms of extracts vs dart ms in situ
MS of Extracts vs. DART MS in Situ

DART MS of Ink on Paper

ESI-MS of Extracts

5 Black Bic Ballpoints

presentation of sample
Presentation of Sample

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

sample held by cover plate hook
Sample Held by Cover-Plate Hook

1/8-inch hole in cover plate gives access to sample.

instrumental conditions
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

raw spectra from chromatogram
Raw Spectra from Chromatogram

Zebra Rubber 80 Ballpoint on Hammermill Fore DP Paper

30 second averages

final spectrum from raw spectra
Final Spectrum from Raw Spectra

Zebra Rubber 80 Ballpoint on Hammermill Fore DP Paper

nist spectral search software
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
nist spectrum search results
NIST Spectrum Search Results

Comparing unknown and highlighted match

Distribution of matches

Unknown

Spectrum of unknown

Spectrum of highlighted match

List of matches

calculating match quality
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.

calculating match quality20
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.

test of paper effects
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.
ballpoint spectrum match qualities
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

spectra matching a ballpoint spectrum
Spectra Matching a Ballpoint Spectrum

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

median match qualities for ballpoint
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

gel ink spectrum match qualities
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

median match qualities for gel ink
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

fluid ink spectrum match qualities
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

median match qualities for fluid ink
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

effects of writing age
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.
ink identification
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.
unknowns that matched incorrectly
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
unknowns that matched incorrectly46
Unknowns that Matched Incorrectly
  • Black Fluids – 10 errors
  • Blue Fluids – 11 errors
acknowledgements
Acknowledgements
  • National Institute of Justice
    • This project was supported by Award No. 2006-DN-BX-K017 awarded by the National Institute of Justice, Office of Justice Programs, US Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this exhibition are those of the author and do not necessarily reflect the views of the Department of Justice.
  • John McClelland, principal investigator
  • Susan Lorge, worked out optimum conditions and acquired library data
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