Analysis of rosin and modified rosin esters in adhesives by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS)

The optimum method for analyzing glyceryl rosinate by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was studied. The performances of dithranol, anthracene, and 2,5-dihydroxybenzoic acid, pyrene, trans,trans-1,4-diphenyl-1,3-butadiene, 9-nitroanthracene, indole-3-acrylic acid and retinoic acid as a matrix agent, and those of sodium trifluoroacetate (NaTFA) and silver trifluoroacetate (AgTFA) as a cationization agent were measured. Dithranol showed higher signal to noise ratio and lower base-line, and AgTFA showed better performance than NaTFA. In this study, however, NaTFA was chosen since the ester peaks with high signal to noise ratios were observed, and the spectra of sodium-cationized molecules are simpler than those of silver-cationized molecules. Rosin esters and modified rosin esters in 22 rubber-based pressure sensitive adhesives and a paper-cement were analyzed. Glyceryl rosinate, glyceryl disproportionated rosinate, pentaerythrityl rosinate and pentaerythrityl hydrogenated rosinate were easily detected despite the fact that rubber-based adhesives are complex mixtures of elastomers, tackifiers, antioxidants and other additives. The detection limit of this method was studied and 2% of glyceryl rosinate in a rubber-based pressure sensitive adhesive was detected. It has been proved that MALDI-TOF-MS is a useful analytical method to analyze rosin and modified rosin esters in adhesives.