Description:
<jats:p>In AMS measurements on small (<jats:italic>m</jats:italic> 400 μg) carbon samples, an <jats:italic>m</jats:italic>-dependence has been noted for the <jats:sup>14</jats:sup>C/<jats:sup>12</jats:sup>C and <jats:sup>13</jats:sup>C/<jats:sup>12</jats:sup>C ratios that is due to the combined effect of contamination and fractionation. A simple formalism is presented to describe the phenomena and to correct measurements on unknowns for their effect.</jats:p>