Detection and Mapping of Chimassorb 944FD Antioxidant Additive in Polyethylene Using TOF-SIMS

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) with either gallium or indium primary beams, has been evaluated as a method to measure the homogeneity of distribution of an antioxidant, Chimassorb 944FD (C944), in linear low-density polyethylene. The parent ion for the oligomer at m/z 599 is sufficiently weak that it could not be used to map the distribution of the additive throughout its most commonly used concentration range (0.1-0.5% (w/w)) in polyethylene. Instead, a mass fragment at m/z 58 was found to be sufficiently clear of interferences that it could be used as a surrogate for the parent ion. As a result, imaging of the antioxidant distribution was possible to concentrations as low as 0.1%, and a linear concentration calibration curve was obtained. The use of an indium primary beam improved the correlation coefficient for the quantitative measurement of C944; moreover, indium reduced the contribution from the polyethylene background at m/z 58 in relation to the total counts acquired.