A few months ago, I posted the results of a study in which the ZDDP contents of several motor oils were determined using neutron activation analysis (which is much more accurate than ICP-AES, the standard method used in industry). Anyway, a paper that includes the details of the study has been accepted for publication (Physics Procedia), but in the meantime, a pre-print version has been posted on arxiv.org:
http://arxiv.org/ftp/arxiv/papers/1502/1502.07261.pdfMost of it is written in pretty plain language, and I figured that it might be of interest to a few of you.
