As a result of the increase in the practice of tattooing, the US Food and Drug Administration has identified a need for improved analytical methods to detect the pigments and potential impurities in the inks. Raman spectroscopy allows for nondestructive identification of compounds and is commonly used in art, archaeology, and forensics; however, the technique has only limitedly been applied to the identification of tattoo pigments. In this study, approximately 30 inorganic, organometallic, and organic pigments were evaluated with Raman spectroscopy by using 532, 633, and 780-nm lasers. Individual optimization of the instrumental parameters was performed for each pigment in order to enhance spectral quality. This research highlights the need for multiple laser interrogation, as the spectra of some pigments were difficult to obtain by using a particular wavelength due to interferences from absorption or fluorescence. However, by using these multiple wavelengths, all pigments could be identified by their unique spectral features. A spectral library of the pigments was created for each laser wavelength and then challenged with pigments from multiple manufacturers. All pigments were identified correctly, and the method is poised to be an effective, noninvasive means for qualitatively identifying tattoo pigments. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.Keywords: Raman spectroscopy; Tattoo inks; Pigments; Spectral library
IntroductionTattoos are formed when ink containing insoluble pigments dispersed in an aqueous medium, often containing alcohol, glycerine, and/or witch hazel, is injected between the dermis and epidermis of the skin. Tattooing has been performed since ancient times and is currently used as an art form, as permanent makeup, and in medical applications.[1] Worldwide, an estimated 120 million people have tattoos [2] with approximately 12% of Europeans [3] and 24% of surveyed US citizens having a tattoo.[4]Regulation of the practice of tattooing and tattoo inks varies worldwide. In the United States, the pigments used in tattoo inks are considered by the Food and Drug Administration (FDA) to be colour additives [5,6] and must be listed in the Code of Federal Regulations. [7] Currently, no colour additives have been approved by the FDA for use in injections such as tattooing. The practice of tattooing in the United States is regulated by state and local jurisdictions with adverse events monitored by the FDA.[1] While reported adverse events have generally involved microbial contamination, [8] such as the August 2015 recall of grey inks with Mycobacterium, [9] awareness of knowledge gaps on tattoo ink components and long-term risks is growing.[3] One concern is the overlap in tattoo pigments that are also used in the printing, plastics, coatings, textiles, and paint industries.[1] The Council of Europe 2008 Report proposed labelling requirements, chemicals that should not be used due to potential toxicity, and maximum allowed concentrations of impurities...
