Quantitative evaluation of europium in blue ballpoint pen inks/offset printing inks tagged with europium thenoyltrifluoroacetonate by spectrofluorometry and ICP-AES

Abstract 

Tagging of writing/printing inks with suitable inorganic taggants such as rare-earth chelates has the potential to help document examiners identify fraud in sensitive written/printed documents. Selection of rare-earth chelates as taggants primarily depends on the satisfactory sensitivity of analytical determination and the absence of the taggants in normal varieties of inks used for document writing/printing. Spectrofluorometric determination of trace amounts of europium in blue ballpoint pen inks and offset printing inks tagged with europium thenoyltrifluoroacetonate was carried out with sodium tungstate solution. Sodium tungstate acts as a specific reagent that enhances the fluorescence intensity of the Eu³⁺ ion. The excitation and emission wavelengths are 270 nm and 605 nm respectively. The results were compared with the data obtained with ICP-AES. Satisfactory recoveries were observed with precision better than 5% RSD and comparable accuracy. Under the optimized experimental conditions, detection limits and quantitation limits were determined. The detection limits obtained by spectrofluorometry and ICP-AES were 0.01 μg/mL and 0.006 μg/mL respectively whereas the limits of quantitation were about 0.03 μg/mL and 0.018 μg/mL respectively. The spectrofluorometric method is rapid, selective, sensitive and accurate for the determination of europium in blue ballpoint pen ink and offset printing inks and may be suitable for application in the examination of sensitive documents to aid in document related crime investigation. The advantages and limitations of the tagging approach and proposed analytical techniques are discussed.

Keywords: Blue ballpoint pen ink, Offset printing ink, Tagging, Europium thenoyltrifluoroacetonate, Spectrofluorometry, Inductively coupled plasma-atomic emission spectrometry (ICP-AES)