Figure 4.

SERS spectra of tetrachlorobiphenyls at concentrations from 10⁻⁴ to 10⁻¹⁰ mol/L in acetone (a) 2,2′,3,3′-tetrachlorobiphenyl; (b) 2,2′,6,6′-tetrachlorobiphenyl; (c) 2,3,5,6-tetrachlorobiphenyl; (d) 3,3′’,5,5′-tetrachlorobiphenyl.