Confidence intervals of fluxes from 13C-MFA using simulated data. The tracers used by Henry et al. (2011) were [1-13C], [6-13C], [U-13C]glucose, and [U-13C]glutamine. (A) Confidence intervals for the oxidative pentose phosphate flux (oxPPP). (B) Confidence intervals for the pyruvate carboxylase flux (PC). The tracers identified with our rational design criteria, [2,3,4,5,6-13C] and [3,4-`13C]glucose, outperformed the tracers selected by Henry et al.