We use extensive DMRG calculations to show that a classification of SU(n) spin chains with regard to the existence of spinon confinement and hence a Haldane gap obtained previously for valence bond solid models applies to SU(n) Heisenberg chains as w
ell. In particular, we observe spinon confinement due to a next-nearest neighbor interaction in the SU(4) representation 10 spin chain.
