Fig. 1. (A) GC–MS analysis of the crude trimethylsilyl derivatized synthetic mixture of 1, 2, 3 and 4; (B) pH-zone-refining CC chromatogram of the separation of 1.3 g portion of the synthetic mixture of 1, 2, 3 and 4.

Fig. 2. pH curves obtained for the pH-zone-refining CCC separation of 1.3 g of 1, 2, 3, 4 dicarboxylic acids mixtures (A) TFA: 30 μl in the sample solution and 400 μl in the stationary phase, and (B) TFA: 60 μl in the sample solution and 800 μl in the stationary phase. For details see Section 2.2.3.

Fig. 3. pH-zone-refining CCC separation of a mixture of maleic (158 mg) and fumaric (308 mg) acids. For details see Section 2.2.4.

Fig. 4. pH-zone-refining CCC separation of a mixture (400 mg) of phthalic (1,2-diCOOH), isophthalic (1,3-diCOOH) and terephthalic (1,4-diCOOH) acids. For details see Section 2.2.5.

Fig. 5. pH-Zone-refining CCC separation of a mixture (600 mg) of cis- and trans-1,4-cyclohexanedicarboxylic acids. For details see Section 2.2.6.

Fig. 6. Calculated [B3LYP/6-31G(d,p)//B3LYP/6-31G(d,p), including zero point vibrational energies] structures of dimers 3 + 3, 3 + 4, and 4 + 4 and their respective dimerization energies.

Fig. 7. Schematic chemohydrodynamic diagram of the pH-zone-refining CCC separation of a mixture of dicarboxylic acids when TFA is used as the retainer acid. Fragments (a) and (a′) represent the processes that take place when sufficient TFA is present in the sample solution/stationary phase. When not enough TFA is present in the system, the process represented in fragment (b) takes place in addition to the processes (a) and (a′).

pH-Zone-refining CCC elution order and pK_a values of cis-, trans-, and positional isomeric dicarboxylic acids

Partition coefficient (K) measurements for pH-zone-refining CCC separation of a mixture of phthalic, isophthalic, and terephthalic acids (3:2:1) using cyclohexane–EtOAc–EtOH–H₂O solvent systems