Comparison of analytical methods for Humic Like Substances (HULIS) measurements in atmospheric particles
Humic-Like Substances (HULIS) are a major contributor to the organic carbon in atmospheric aerosol. It would be necessary to standardize an analytical method that could be easily and routinely used for HULIS measurements. We present one of the first comparisons of two of the main methods in use to extract HULIS, using I) a weak anion exchanger (DEAE) and II) the combination of two separation steps, one according to polarity (on C18) and the second according to acidity (with a strong anion exchanger SAX). The quantification is performed with a TOC analyzer, complemented by an investigation of the chemical structure of the extracted fractions by UV-Visible spectroscopy. The analytical performances of each method are determined and compared for humic substances standards. These methods are further applied to determine the water extractable HULIS (HULISWS) and the 0.1 M NaOH alkaline extractable HULIS (HULIS T) in atmospheric aerosol collected in an Alpine Valley during winter time. This comparison, although on a limited batch of samples shows that the simpler DEAE isolation procedure leads to higher recoveries and better reproducibility than the C18-SAX procedure, and might therefore be preferable.