Rapid and simultaneous determination of nine volatile solvents in ink entries with improved gas chromatography

Abstract

Volatile compounds such as alcohols and ethers are added into ballpoint pen inks, gel pen inks and water-based rollerball pen inks as humectants or solvents. The composition of solvents in inks and their amounts of evaporation are critical evidence for identifying the types of pens or dating ink entries. Relative quantification methods using gas chromatography (GC) or gas chromatography coupled to mass spectrometry (GC/MS) were employed to analyze alcohols and ethers in most previously reported studies, but they were not convenient for researchers of the same field to compare results. Besides, those methods are time-consuming, with an average time of 23−36 min per run. Therefore, in this work a rapid quantification method was established to simultaneously determine nine volatile solvents commonly existed in ink entries, including ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, diethylene glycol, triethylene glycol, benzyl alcohol, 2-phenoxyethanol (PE) and diethylene glycol monoethyl ether (DGME), while 1,3-butanediol was used as the internal standard. A GC system equipped with flame ionization detector (FID) was adopted to separate the nine target analytes. The analysis time was reduced to 9–12 min. The linearity of the calibration curves was good in the ranges of 10–3000 ng/cm for all target analytes, and Pearson correlation coefficients were all greater than 0.999. The results indicate that the established method provides sensitive, precise, and accurate quantification of nine volatile solvents in ink entries. What’s more, this method raises analytical efficiency greatly and has lower requirements of instruments, showing promising application in questioned document examination and ink dating.