Dear Listmembers

To measure O-isotope ratios of biogenic phosphates one has to first
chemically isolate the material as silver phosphate. I can understand
why this treatment is necessary for biogenic phopshate, but is this
necessary for phosphate minerals (apatite, monazite and xenotime)?  I
would be interested to hear if anyone has successfully or
unsuccessfully extracted oxygen from phosphate minerals by either CO2
laser ablation (+BrF5) or conventional extraction for 18/16O
analysis, without first converting to silver phosphate.

Regards
Kevin Faure