Lots of sources of information. For example, see: 

http://www.cdc.gov/niosh/docs/2009-125/pdfs/2009-125.pdf 

http://nanoparticles.org/standards/ 

Thank you.  I will read these documents.Hope I get information for water metric.

I suggest making fresh standards as long term storage of nanoparticles would lead to agglomeration in most of the cases