Amino acids as precursors of trihalomethane and haloacetic acid formation during chlorination

Twenty amino acids were chlorinated and examined for the formation of trihalomethane (THM) and haloacetic acid (HAA). The amino acids exhibited a high Cl₂ demand (3.4-10 mg Cl₂ mg^-1 C) but low THM formation (<4.19 μg mg^-1 C) except for tryptophan and tyrosine (45.8 - 147 μg mg^-1 C). Large variation in HAA yield occurred among the amino acids (from not detectable to 106 μg mg^-1 C). One group of amino acids, possessing chain structures, exhibited a slow increase in HAA formation (<6.2 μmol mol^-1 amino acid or <11.3 μg mg^-1 C) as the chlorine demand increased (3.4-8.9 mol Cl₂ mol^-1 amino acids). The other group of amino acids, containing ring structures (including tryptophan, tyrosine, histidine, phenylalanine, and proline) and two amino acids with chain structures (aspartic acid and asparagine), showed a fast increase in HAA formation (16-96 μmol mol ^-1 amino acid or 27-106 μg mg^-1 C) with the increase in chlorine demand (5.2-15.9 mol Cl₂ mol^-1 amino acid). The ratios of TCAA to DCAA (mol/mol), derived from the amino acids, ranged between 0.01 and 1.10.