We are normally using the NBS-19 (TS-limestone) to calibtate our Optima
machine for oxygen. normally we are too worried about the oxygen value as we
use the delat13 to correct radiocarbon ages.
Nevertheless we decided to go back to the entire 13C and 18O-calibration.
We always used the -2.20 for the NBS oxygen value. Is that actually the
value of the mineral or the CO2 produced with 100% H3PO4 at 25degrees? I am
really not sure about that.

Thanks a lot.

Dr. Tanya ErtunÁ

NERC Radiocarbon Laboratory
Scottish Enterprise Technology Park
Rankine Avenue
East Kilbride
Glasgow G75 0QF

Tel.: 0044/1355/260037
Fax: 0044/1355/229829
E-mail: [log in to unmask]