1. Differentiation of blue ballpoint pen inks by positive and negative mode LDI-MS 
M. Gallidabino, C. Weyermann, R. Marquis 
Forensic Science International 
Volume 204, Issue 1, Pages (January 2011)
DOI: /j.forsciint
Copyright © 2010 Elsevier Ireland Ltd Terms and Conditions

2. Fig. 1
Examples of irradiance effects on resolutions (m/Δm) of selected peaks. Peak resolution is decreasing as a function of nominal laser irradiance in LDI-MS positive and negative modes, represented here by molecular ions of dyes BV3 and SB38, respectively. The resolution was observed to decrease importantly when using laser irradiance values over 72 for positive and over 80 for negative mode, respectively. Right dotted and left dash-dotted lines represent nominal irradiance values chosen to acquire ballpoint inks spectra in positive and negative modes, respectively.
Forensic Science International  , DOI: ( /j.forsciint )
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3. Fig. 2
Representation of irradiance effect on spectrum maximal intensity. Signal maximal intensity (mV) increases in function of nominal laser irradiance in LDI-MS positive and negative modes. Right dotted and left dash-dotted lines represent nominal irradiance values chosen to acquire ballpoint inks spectra in positive and negative modes, respectively.
Forensic Science International  , DOI: ( /j.forsciint )
Copyright © 2010 Elsevier Ireland Ltd Terms and Conditions

4. Fig. 3
Examples of irradiance effects on RPA values. (a) Shows effects on BV3 in positive mode: RPA372 (BV3) decreased as a function of nominal laser irradiance, while RPA358 (BV3 – Me) and RPA344 (BV3 – 2Me) increased. This effect is particularly marked over a laser irradiance value of 64. (b) Shows similar effects on SB38 in negative mode: RPA815 (SB38+SO3H) decreased as a function of nominal laser irradiance, while RPA735 (SB38) and RPA895 (SB38+2SO3H) increased. This effect is particularly marked over a laser irradiance value of 84. Dotted line in (a) and dash-dotted line in (b) represent nominal irradiance values chosen to acquire ballpoint inks spectra in positive and negative modes, respectively.
Forensic Science International  , DOI: ( /j.forsciint )
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5. Fig. 4
Effects on signal resolution of SB38 peaks in LDI-MS negative mode when the nominal laser irradiance was increased from 80 (a) to 92 (b). In negative spectra, signal corresponding to SB38 is a mixture of its radical anion [CuPc(SO3H)2]− and the respective anionic species CuPc(SO3H)(SO3−). The summed isotopic pattern between this species is visible when laser irradiance is suitable (a). However, the isotopic information was lost when the laser irradiance was set too high and as a consequence only the average mass could then be determined (b).
Forensic Science International  , DOI: ( /j.forsciint )
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6. Fig. 5
Structure of copper phthalocyanines (CuPc) derivatives identified in blue ballpoint inks together with m/z values of corresponding ions. The difference between these molecules lies in the number of sulfonic acid functional groups added to the basic structure.
Forensic Science International  , DOI: ( /j.forsciint )
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7. Fig. 6
Structure of two dyes detected in inks using LDI-MS negative mode, together with theoretical m/z values of corresponding negative ions.
Forensic Science International  , DOI: ( /j.forsciint )
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8. Fig. 7
LDI positive (a) and negative (b) mass spectra of ballpoint pen #2. In positive mass spectrum, only the dye BV3 and its fragmentation products were identified (m/z=372.2, and 344.2). On the other hand, in negative mass spectrum numerous dyes were present: AB9 (m/z=170.2 and 185.2), AB92 (m/z=313.5 and 628.0), SB38 (m/z=735.0) and its mono-sulfonic acid derivative (m/z=815.0). (c) Shows the HPTLC plate of the same ink. The dye SB38 (spot 1), AB9 (two spots 2), AB92 (spot 3) and BV3 (three spots 5) were identified by comparison of the retention times and colors with reference substances. While the retention time of spot 4 did correspond to the reference substance BG4, the identification could not be confirmed by LDI-MS results.
Forensic Science International  , DOI: ( /j.forsciint )
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