ACS Style Guide 2006 edition addresses how to cite an MSDS.
Hard copy (paper) MSDS
Titanium Dioxide; MSDS No. T3627; Mallinckrodt Baker: Phillipsburg, NJ, November 12, 2003.
MSDS obtained from an Internet search
Titanium Dioxide; MSDS No. T3627; Mallinckrodt Baker: Phillipsburg, NJ, November 12, 2003. http://www.jtbaker.com/msds/englishhtml/t3627.htm (accessed 4/15/04).
MSDS obtained from a database source such as CCOHS
Titanium Dioxide; MSDS No. T3627; Mallinckrodt Baker: Phillipsburg, NJ, November 12, 2003. Available from Canadian Centre for Occupational Health and Safety. http://ccinfoweb2.ccohs.ca/msds/Action.lasso?-database=msds&-layout=Display& - response=detail.html&-op=eq&MSDS+RECORD+NUMBER=3767394&-search (accessed 4/15/04).