Mike, et al,
When the WR star blasts away their final hydrogen shell (velocities >2000 km/s) the chemical consistency of the subsequent shell material is:
Hydrogen/ Helium 98.5%
Nitrogen 0.1%
Carbon 0.35%
Oxygen 1%
See Section 6.3 of the following document for even further detail.
http://adsabs.harvard.edu/cgi-bin/bi...6A...305..229G