Serum nicotine binding capacity was determined by measuring bound and free concentrations of nicotine at equilibrium.

<p>Kd values (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114366#pone-0114366-g008" target="_blank">Fig. 8</a>) were used to calculate total antibody concentrations according to the law of mass action equation: Kd = [Nic][IgG]/[Nic-IgG]. Comparisons between groups were conducted by unpaired two-tailed <i>t</i>-test; *p<0.04; **p<0.01; ***p<0001.