An Investigation into the Photolytic Degradation Products of Tattoo Pigments

Author: Tristan Fraser

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Fraser, Tristan, 2023 An Investigation into the Photolytic Degradation Products of Tattoo Pigments, Flinders University, College of Science and Engineering

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Tattoos are adornments made on one’s body by injecting inks into the dermal layer of skin, often as a form of self-expression or affiliation with a group (1). With rising popularity has come an increased demand for tattoo removal procedures (2, 3), achieved most commonly using laser tattoo removal procedures (4-6). Tattoo pigments have come under concern for their potential to produce toxic compounds when irradiated with a laser (7), and some pigments have been banned. Though previous literature has investigated the degradation of pigments from all three categories, the majority of research has focused on azo pigments (1, 8-15) with phthalocyanines being investigated the least (11-13, 16). Some of the degradation products reported include benzene, chlorobenzene, o-toluidine, and hydrogen cyanide. The research present here, therefore, aimed to further investigate the laser induced degradation of the phthalocyanine pigments, pigment blue 15 (PB 15), pigment green 7 (PG 7), and pigment green 36 (PG 36) and the polycyclic pigment, pigment violet 1 (PV 1). Furthermore, a simplistic model was developed to determine the worst-case scenario for exposure to laser induced degradation products and determine whether they could be harmful with comparison to safety limits.

Experiments were performed using a laser desorption/ionisation-time of flight-mass spectrometer (LDI-ToF-MS) to see if it could be used as an alternative method to laser irradiation followed by analysis with either gas chromatography or liquid chromatography mass spectrometry (GCMS and LCMS). This was achieved by depositing inks and pigments (1 mg/mL in isopropanol) onto a ground steel sample plate for analysis in a Bruker Autoflex III Matrix assisted LDI-ToF-MS (MALDI-ToF-MS) operating with a wavelength of 1064 nm. Though many of the samples displayed complex spectra, none of the samples displayed fragments with the expected m/z of laser irradiation degradation products previously reported in literature. It also seemed unlikely for these previously reported degradation products to have been lost as either a neutral or negatively charged fragment.

The LDI-ToF-MS spectra was used in conjunction with Raman spectra gathered, with a XploRA plus Horiba Scientific Confocal Raman microscope, and X-Ray Fluorescence spectra, collected with a Bruker Tracer III-V pXRF, to determine the pigment composition of the tattoo inks. The use of all three techniques indicated that the Light Purple (LP) and Lemon Yellow (LY) inks contained at a pigment not reported on their label while the Grasshopper Green (GG) and Dragon Green (DG) inks exhibited Raman spectra consistent with Pigment Green 7 (PG 7) and Pigment Yellow 14 (PY 14), and an LDI-ToF-MS consistent with Pigment Green 36 (PG 36). Only PG 7 and PY 14 are marked on the labels for the DG and GG inks. An attempt was made to present a complete assignment of vibrational modes to the peaks observed in the Raman spectra. Peaks previously assigned in literature were collated and peaks with no assignment were given one using generalised observations of the Raman shifts for the vibrational modes of intramolecular bonds (17, 18).

A novel approach to the laser irradiation of tattoo inks and pigments was designed to analyse the degradation products resulting from laser settings similar to those used in tattoo laser removal procedures. Tattoo pigments were suspended in a mixture of water, isopropanol and PVP solution (50% w/v). The pigment suspensions and the tattoo inks were deposited onto cellulose substrates using a sponge to apply an even coat over a 5 cm by 5 cm area. Once dry, strips were cut from the samples and secured in HPLC/GCMS vials. The samples were then irradiated with 20 pulses from a 532 nm Q-switched neodymium: Yittrium doped Garnet Laser (Nd:YAG laser) in 5 spots on each sample strip. The headspace of each sample was immediately analysed with GCMS. The samples were then extracted with ethyl acetate and analysed with LCMS. The GCMS analysis indicated that benzene was present in PB 15, PG 36, PV 1, PY 14, and Pigment Yellow 74 (PY 74). Toluene was present in all


pigments except for PG 7, chlorobenzene was present only in PG 7 and o-Xylene was present in PG 36. Finally, PY 74 was found to have produced styrene which appears to have never previously been identified in literature regarding the laser irradiation of tattoo pigments. Interestingly, though PB 15 did not produce styrene and is the only pigment present in the Royal Blue (RB) ink, styrene was observed to have been produced in the RB ink. Benzene was observed in all inks, Toluene was observed in the DG, LY, Golden yellow (GY), Bright Orange (BO), Bright Red (BR), and Cherry Bomb (CB) inks. Chlorobenzene was present in the DG, BR, and CB inks and o-xylene was present in the CB and inconclusively present in the BR inks. The BO ink displayed a peak with a GC retention time consistent with styrene and o-xylene that had a mass spectrum, inconsistent with either compound. It could not be identified with the single quadrupole mass spectrometer. Finally, the LCMS analysis presented very complex chromatograms for all pigment and ink samples, however, no peak could be identified when the mass spectra of the peaks were compared to those of degradation products previously reported in literature. Both the GCMS and LCMS analysis were difficult due to low signal to noise ratios in the mass spectra. Using triple quadrupole mass spectrometers would increase sensitivity while using tandem mass spectrometers would allow for the identification of peaks that don’t match previously reported mass spectra.

Finally, a simple and novel mathematical model was developed to determine a worst-case scenario for the exposure to the degradation products identified by GCMS and to compare them to safety limits. The model assumes a tattoo size of 100 cm2 is comprised of a single ink and contains 2.53 mg/cm2 of pigment (9). It also assumes that the tattoo is the only source of carbon, that the pigments only undergo intramolecular reactions and rearrangements and that all pigment molecules degrade. For comparison to safety limits, the concentrations were determined as if the degradation occurred in an Australian women of median height (161 cm), weight (68.2 kg), and body mass index (BMI)(26.3) which would have an estimated blood volume (EBV) of 4.37 L and estimated minute ventilation of 6.5 L of air. These assumptions were used to calculate the mass of styrene, o-Xylene, benzene, chlorobenzene and toluene that could be produced in isolation then converted to either an estimated tattoo removal – blood concentration (ETR-BC) or an estimated tattoo removal – body weight concentration (ETR-WC) and compared to an inhalation safety limit or, when inhalation data was unavailable, an ingestion safety limit, the safety limits were adjust to assume that exposure occurred for 1 hour and for the absorption rate of each compound. The safety limit for; benzene was 459.9 mg/L, toluene was 69.11 mg/L, chlorobenzene was 0.0571 mg/kg of body weight, styrene was 3000 mg/L. and o-Xylene was 2870 mg/L. Only chlorobenzene produced by PG 7 was found to exceed the adjusted safety limit as it has a worst-case scenario ETR-WC of 23.8 mg/kg of body weight.

Keywords: Tattoo, Analytical Chemistry, Tattoo Degradation, Laser Induced Degradation, photolysis, Tattoo photoloysis, Tattoo Laser Removal

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Science and Engineering
Supervisor: Claire Lenehan