A modified method of high molecular weight adsorbable organic chlorine measurement in saline water: Dialysis pretreatment.

Adsorbable organic halogen is a mean to quantify total organic halogen, which is an important toxicity indicator in disinfection byproduct studies. However, quantification of low concentrations of adsorbable organic chlorine (AOCl) formation in seawater chlorination using the USEPA Method 9020B was found inaccurate due to the presence of high concentrations of chloride. In this study, a dialysis-based pretreatment technique was proposed, optimized and adopted to eliminate the interference of chloride in quantifying low concentrations of AOCl in seawater. A volumetric ratio of dialysis samples to continuous-flow deionized water at 1:1200 was found sufficient to remove over 99% of chloride. As a result, chloride to AOCl ratios can be reduced to less than 20,000, and the interference from chloride can thus be eliminated. The detainment of AOCl by the dialysis pretreatment depends on the molecular weight cutoff of the cellulose seamless dialysis membrane currently used, which was determined to be around 320 to 500 Da. The dialysis pretreatment can be used to measure AOCl concentrations in chlorinated seawater samples at pH 6.5 to 10.