From this paper... http://pubs.acs.org/doi/pdf/10.1021/jp020363g there is a graph... Which I've been told the M means moles per litre. I now have another graph from this paper... http://pubs.acs.org/doi/abs/10.1021/jp9937407 .... Which has mM, so is this mM/L or just milli moles? Sorry for the basic question and thanks for any help!