There was some increased data variation for long-chain compounds such as C10-C10-DADMAC particularly at high concentrations. This result illustrates a weakness of the current approach; PA fiber sorption is increasingly nonlinear with surfactant concentration, and therefore, in the high concentration range, a small error in measured CPA results in a large variation in calculated Cw. That is to say, at high concentrations, nLF,PA is low, and the exponent of eq 4 (i.e., 1/nLF,PA) is high, which augments the errors in CPA and the sorption parameters, leading to an increased uncertainty in Cw. In addition, when CPA is high and close to qmax,PA, the denominator of eq 4 approaches 0, and the estimation of Cw from CPA becomes unstable.