In a second experiment, pairs of TNT-PNA probes of the same length were mixed in various different ratios. The correlation between the expected and measured quantities of these different TNT-PNA ratios is shown in Figure 7 . It can be seen that there are simple linear correlations between the expected and measured ratios. The blue crosses in Figure 7 indicate the results of experiments where the two TNT-PNA probes with the same sequences but with different isotopomeric tags were mixed, i.e. the whole TNT-PNA probes were isotopes of each other. The measured ratios for these probes closely match the expected ratios.