I would like to isolate oxygen from water for isotopic analysis, so I can
calibrate the oxygen standard in a mass spectrometer.  I was thinking
electrolysis to separate H and O, but would any fractionation occur during this
process?

Conversely, if anyone knows where/how I can purchase an oxygen gas standard to
calibrate the mass spec, I would appreciate any input.  Thanks,
Remy Okazaki