The relationship between TOX formation and spectral changes accompanying chlorination of pre-concentrated or fractionated NOM

The change in the absorbance upon chlorination (the differential absorbance, ΔA) of natural organic matter (NOM) that has been concentrated, isolated, and/or fractionated from five sources was explored as a possible indicator of the formation of total organic halogen (TOX) in the samples. The results demonstrate that concentration and isolation of NOM using techniques that are currently in widespread use does not significantly alter the TOX–ΔA272 relationship that applies to the unprocessed NOM. However, when such samples are fractionated, the TOX–ΔA272 relationships for the different fractions are not identical. In particular, when the hydrophobic and hydrophilic neutral fractions of NOM are chlorinated, the amount of TOX formed per unit of A272 destroyed is significantly larger than the corresponding value for other NOM fractions. This observation might reflect the relatively high content of proteins and other amino acid structures that can be disinfection by-product precursors but that absorb little or no light at 272 nm.