Hybrids of single stranded DNA and single walled carbon nanotubes (SWCNTs) have proven very successful in selecting various chiralities and, recently, enantiomers of carbon nanotubes using aqueous two-phase (ATP) separation. This technique sorts objects based on small differences in hydration free energy, which is related to corresponding small differences in structure. Separation by handedness requires that a given ssDNA sequence adopt different structures on the two SWCNT enantiomers. In this talk we will discuss two aspects of the ATP separation process. Firstly, we study the physical basis of such selectivity using a coarse grained model to compute the energetics of ssDNA wrapped around an SWCNT. Our model suggests that difference by handedness of the SWCNT requires spontaneous twist of the ssDNA backbone. We also show that differences depend sensitively on the choice of DNA sequence. Secondly, we present a method by which measurements of partitioning by ATP can be used to rank quantitatively the solute solvation free energy.