Introduction
Humic-like substances (HULISs) are a group of substances with no specific chemical structure, resembling the humic substances found in soil and water. They constitute the main component of water-soluble organic matter in the atmosphere and are known to exhibit absorption properties in the ultraviolet to visible light range, potentially influencing atmospheric radiative balance. Understanding their environmental dynamics is therefore crucial. However, existing analytical methods for HULISs involve labor-intensive pretreatment steps, which can lead to reduced quantification accuracy and hinder improvements in analytical efficiency. To address this issue, this study aims to develop a system for HULIS analysis using high-performance liquid chromatography (HPLC) equipped with an integrated sample cleanup mechanism, enabling the direct analysis of atmospheric particles through their simple extraction using water.
Methods
The automated system for sample cleanup and detection consists of four HPLC pumps, an autosampler, a cleanup column (Oasis-HLB, 3 mmφ × 20 mm, Waters), a column heater, a six-port valve, and a photodiode array detector (DAD) . The following steps were performed in accordance with a time program:
- Before sample injection, the flow path was cleaned with ultrapure water.
- The cleanup column was conditioned with methanol and ultrapure water.
- The system was acidified with hydrochloric acid (pH = 2).
- After injecting the sample, the HULISs in the acidified sample were adsorbed onto the column.
- HULISs were eluted with a 2% ammonia–methanol solution (w/w) and detected using the DAD.
Results and Conclusions
This automated pretreatment analysis system achieved highly favorable peaks. The recovery rate of a 100 mg/L standard fulvic acid solution was 91.2±0.9% with this method, under optimal conditions. We are planning to optimize the time program conditions and apply this system to actual atmospheric samples.
