I understand that diastereoisomers are separable, but how the 2*5 enantiomers that make the 5 enantiomer pairs get separated to form 10 (not 5) fractions when a chiral sorbent is used?
Consider that your pairs are S1, R1; S2, R2; S3, R3; S4, R4; S5, R5. With an achiral sorbent both Sn and Rn interact the same given the achiral mobile phase too, but with a chiral sorbent, say Sx, you get S1:Sx, R1:Sx; S2:Sx, R2:Sx,... R5:Sx, which act as diastereoisomers, and hence differently wrt to the achiral mobile phase