Determination of photoformation rates and scavenging rate constants of hydroxyl radicals in natural waters using an automatic light irradiation and injection system

Photoformation rates and scavenging rate constants of hydroxyl radicals ((OH)-O-center dot) in natural water samples were determined by an automatic determination system. After addition of benzene as a chemical probe to a water sample in a reaction cell, light irradiation and injection of irradiated water samples into an HPLC as a function of time were performed automatically. Phenol produced by the reaction between (OH)-O-center dot and the benzene added to the water sample was determined to quantify the (OH)-O-center dot formation rate. The rate constants of (OH)-O-center dot formation from the photolysis of nitrate ions, nitrite ions and hydrogen peroxide were comparable with those obtained in previous studies. The percent of expected (OH)-O-center dot photoformation rate from added nitrate ion were high in drinking water (97.4%) and river water (99.3%). On the other hand, the low percent (65.0%) was observed in seawater due to the reaction of (OH)-O-center dot with the high concentrations of chloride and bromide ions. For the automatic system, the coefficient of variance for the determination of the (OH)-O-center dot formation rate was less than 5.0%, which is smaller than that in the previous report. When the complete time sequence of analytical cycle was 40 min for one sample, the detection limit of the photoformation rate and the sample throughput were 8 x 10(-13) M s(-1) and 20 samples per day, respectively. The automatic system successfully determined the photoformation rates and scavenging rate constants of (OH)-O-center dot in commercial drinking water and the major source and sink of (OH)-O-center dot were identified as nitrate and bicarbonate ions, respectively. (c) 2006 Elsevier B.V All rights reserved.