Air-water Henry's law constants for PCB congeners: Experimental determination and modeling of structure-property relationship.

A modified gas-purging technique was used for the determination of Henry's law constants (HLCs) for four non-ortho- and eight mono-ortho-substituted polychlorinated biphenyls (PCBs). The method involves measurement of a compound's concentration in only the water phase while that compound is being stripped isothermally from the solution at a known gas flow rate. HLCs were calculated from the slope of a plot of ln(Cn) versus (1/V)n, where (Sigma 1/V)n = 1/V0 + 1/V1 + ... + 1/V(n-1). The HLCs ranged from 5.6 to 21.8 Pa m3/mol, with an average precision of 13%, and they are comparable to values in the literature. Meta-analysis technique and principal component regression (PCR) were applied to model the relationship between experimentally determined HLC values of 94 PCB congeners and the congeners' structures. Cross-validation yields an optimal model with two principal components. Statistical analysis suggests that HLCs of PCBs are primarily affected by meta-chlorine substitution, a relationship which has never been discussed in the literature. The substitution of chlorines on the biphenyl rings generally leads to smaller HLCs. The predicted HLCs are in good agreement with the experimentally determined values.