[Classification of blue gel inks and investigation of change rule of the ink with writing age using pyrolysis gas chromatography].

ABSTRACT

Gel ink pen (neutral pen) is a new popular pen. Its coloring matters are usually pigments which could not be extracted by water or organic solvents. Therefore, the methods of gas chromatography and high performance liquid chromatography for analyzing the inks of ball-point pen and water-based pen cannot be used here. There are no effective methods to identify gel inks in forensic science up to now. Pyrolysis gas chromatography (Py-GC) was used to analyze 65 different blue gel inks in this report. The pyrolysis was performed with a CZ-100 pyroprobe system using a coil filament with a quartz sample tube at 770 degrees C for 10 s. Agilent-6890N Gas Chromatograph was used with a nitrogen-phosphorus detector. A DM-5 Dikma Technology column (30 m x 0.32 mm x 0.25 microm) was used. Based upon the number and retention time of peaks in the pyrograms, the gel inks were separated into 3 classes. The most of the gel inks fell into the second group which have two characteristic peaks of copper phthalocyanine pigment. The results showed that the retention times and ratio of the peak areas were stable and reproducible. The writing age of blue gel ink was primarily investigated by the relative change rule of the main components in the ink, and the curves of writing age was obtained.