Hi Nick,
here's one more ..
can you add "Ionic strength"?
http://en.wikipedia.org/wiki/Ionic_strength
I wouldn't know where to put it - it could be seen a kind of concentration (in fact it's more or less a sum of weighted concentrations) - so maybe it could be a sibling of other concentration entries (but maybe Nicolas or others may have smarter ideas about it).
Thank you!!
Best, Wolf
Anonymous
created SBO:0000623 (ionic strength) as a child of quantitative systems description parameter. It does not really fit with other concentration terms since they deal with individual entities. Thanks for the request Wolfram!