Unexpected Historical Trends in Elemental and Stable Isotope of Carbon and Nitrogen Composition of Brazilian Banknotes: A Potential Tool for Money Counterfeiting Analysis

In this paper, we did a broad prospective survey on the use of elemental concentration and carbon and nitrogen isotope ratios of Brazilian banknotes as a forensic tool to help elucidate cases of money counterfeiting. We analyzed C and N concentrations, and carbon (expressed as 13C) and nitrogen (expressed as 15N) isotopic ratios of 177 banknotes issued from 1944 to 2013 of different banknote denominations and with several replicates of the same denomination. As money paper is composed of vegetal C3 plant constituents, such as cotton, wood, or linen, we compared our results to known Brazilian C3 plant elemental and isotopic composition. We found a lower coefficient of variability (CV) among same year banknotes, compared to plants. The CVs were nearly constant with the banknote age for the parameters analyzed. As in nature, the lowest CVs were observed for carbon concentration and 13C values (1%), followed by nitrogen concentration and C:N ratio (14%), and 15N values (24%). We found historical trends in banknotes’ N concentration, C:N ratio and 13C values. The historic trends found here open the opportunity to use such changes as a forensic tool in money counterfeiting analysis. However, more studies are needed to establish a solid basis for this purpose, such as the analysis of counterfeit banknotes, banknotes from different countries, and fiber analysis.