MOLAR MASSES AND RADII OF HUMIC SUBSTANCES MEASURED BY LIGHT-SCATTERING

A bulk aquatic natural organic material (NOM) was characterized by hig h-performance size exclusion chromatography (HPSEC) coupled with multi -angle laser light scattering (MALLS), UV-Vis, and refractive index de tection. This technique was used to measure the molar mass and radius of the natural organic matter in solution. Results indicate that the N OM aggregates to a large extent at the concentrations used in this stu dy (5...15 mg mL(-1)). The solution conditions of pH and ionic strengt h were also shown to affect the measured size of NOM. The number and t ype of HPSEC columns also influenced these measurements. The importanc e of using multiple detectors was illustrated by peaks that were not d etected by all the detectors. While these data are preliminary and hav e large errors associated with them, it is nevertheless an indication that HPSEC-MALLS can be used to investigate the effects of solution co nditions and aggregation on the size of humic substances in solution.