Preventing drift of oxygen isotopes of CO-in-air stored in glass sample flasks: new insights and recommendations.

It is known that the oxygen isotope composition of CO-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes.