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Pigment Characterization Reference pigments, dried inks (D-ink), and ink extracts (E-ink) were compared using FTIR, NMR, XRD, Raman, EDX, and ICP-OES to identify the likely pigments in the inks. FTIR Spectra Figure 2 depicts the FTIR spectra of pig- ments obtained from ink extracts (E-LY, E-GY, E-GR, and E-BO) and reference pig- ments (PY14, PY65, PB15, and PO13) between 1,900 cm -1 to 600 cm -1 . The full range of the spectra (4,000 cm -1 to 550 cm -1 ) and assignment of functional groups to the FTIR spectra can be found in Supplemental Figure S1 and Table S1. Moreover, PO13 had characteristic peaks at 1,653, 1,493, 1,371, 1,331, 1,235, 1,144, 1,044, 998, 907, and 682 cm -1 . These peaks were not observed in the ink extracts, which indicates that none of the ink extracts contained PO13—or if they did, PO13 presented at levels below the instrumental limit of detection. Similarly, PY65 had distinctive absorption peaks at 1,546, 1,302, 1,187, 1,135, 1,030, and 763 cm -1 that were not observed in the ink extracts. This finding indicates that PY65 was not present in any of the inks—or if it was, it was present at levels below the instru- mental limits of detection. The IR spectral of PB15 shows several peaks at 1,612, 1,464, 1,421, 1,331, 1,287, 1,166, 1,119, 1,087, 901, 877, 778, and 725 cm -1 . The absence of these peaks in LY ink indicates that the FTIR spectra could not confirm the existence of this pigment in this ink. Moreover, PY14 had peaks at 1,670, 1,515, 1,360, 1,245, 1,171, 950, 860, 782, 750, and 619 cm -1 that were correlated with the presence of C-Cl and N-C=O bonds (Bauer et al., 2020). All four ink-extracts yielded FTIR spectra that appeared very similar to the spectra from PY14, indicating that they likely contained PY14. FTIR spectra from the dried inks (D-LY, D-GY, D-GR, D-BO) were consistent with those of the extracted inks (Supplemen- tal Figure S2). NMR Analysis In case the pigments were at concentrations below the limits of detection for the FTIR study, NMR analysis was also undertaken. Figure 3 shows the 13 CNMR spectra for PY14, PY65, and PO13 along with dried inks from LY, GR, BO, and GY inks. NMR spectra of
FIGURE 2
Spectrum of Reference Pigments and Tattoo Inks Using Fourier Transform Infrared (FTIR) Spectroscopy
Note. A magnification of the infrared (IR) spectra is in the 1,900–600 cm -1 range with a resolution of 4 cm -1 to demonstrate the characteristics more accurately. IR spectra comparison of inks and pigments reveals the presence of PY14 instead of PY65 in the lemon yellow (LY) ink. The golden yellow (GY), golden rod (GR), and bright orange (BO) inks did not have PO13. E-BO = ink extract, bright orange; E-GR = ink extract, golden rod; E-GY = ink extract, golden yellow; E-LY = ink extract, lemon yellow; PB = pigment blue; PO = pigment orange; PY = pigment yellow.
FIGURE 3
Spectrum of Reference Pigments and Tattoo Inks Using 13 C Solid- State Nuclear Magnetic Resonance (NMR) Spectroscopy
Note . Spectral analysis confirms the presence of PY14 in all inks, with PO13 in the bright orange (BO) ink and PO13 absent in golden yellow (GY) and golden rod (GR) inks. NMR spectra also confirmed that the lemon yellow (LY) ink did not have PY65. C = copper; PO = pigment orange; PY = pigment yellow.
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Volume 88 • Number 2
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