Classification of prepaid cards based on multivariate treatment of data obtained by X-ray fluorescence analysis

Two hundred prepaid cards, which had been used in Nagoya-city's subway in Japan, and another 32 prepaid cards (11 were real turnpike cards, 20 were counterfeit cards and 1 was a white card) were evaluated by X-ray fluorescence (XRF) without any pre-treatment. A preliminary investigation was performed on 200 prepaid cards in order to find an identification method for the turnpike cards. By plotting the relative intensity of titanium versus that of iron obtained by XRF, the cards were clearly classified into seven groups. On the other hand, the cards could be divided into four groups by a multivariate analysis using the relative intensities of five elements such as chlorine, calcium or tin, titanium, iron and barium. Using these results to classify the Japanese turnpike cards, they were divided into three groups or two groups. One of three groups or two groups was the counterfeit card group.