Characterization of dissolved organic matter using high-performance liquid chromatography (HPLC)–size exclusion chromatography (SEC) with a multiple wavelength absorbance detector

Abstract

High-performance liquid chromatography–size exclusion chromatography (HPLC–SEC) coupled with a multiple wavelength absorbance detector (200–445nm) was used in this study to investigate the apparent molecular weight (AMW) distributions of dissolved organic matter (DOM). Standard DOM, namely humic acid, fulvic acid and hydrophilic acid, from the Suwannee River were tested to ascertain the performance and sensitivity of the method. In addition to four compounds groups: humic substances (Peak 1, AMW 16kD), fulvic acids (Peak 2, AMW 11kD), low AMW acids (Peak 3, AMW 5kD), and low AMW neutral and amphiphilic molecules, proteins and their amino acid building blocks (Peak 4, AMW 3kD), an new group that appears to include low AMW, 6–10kD, humic substances was found based on investigating the spectra at various elution times. The spectroscopic parameter S>365 (slope at wavelengths >365nm) was determined to be a good predictor of the AMW of the DOM. The detector wavelength played an important role in evaluating the AMW distribution. For some fractions, such as the humic and low AMW non-aromatic substances, the error in measurement was ±30% as determined by two-dimensional chromatograms detected at an artificially selected wavelength. HPLC–SEC with multiple wavelength absorbance detection was found to be a useful technique for DOM characterization. It characterized the AMW distributions of DOM more accurately and provided additional, potentially important information concerning the properties of DOM with varying AMWs.