Determination of trace organic compounds by separation based on polarity in complex air sample extract of PM2.5 from urban sources

Abstract

Atmospheric particulate matter (PM) is considered to pose a significant risk to human health due to its ability to remain in the respiratory tract. However, little is known about the organic composition of these PM. The organic portion of airborne PM consists of a highly complex mixture of compounds that represent major sources of air pollution. This study aims to develop a sensitive method for separating this complex organic mixture into eight individual fractions, arranged in increasing polarity from non-polar to polar. This approach will improve our understanding of the chemical composition of airborne fine particulate matter, allowing for the identification and quantification of a greater number of organic compounds. An advanced silica-gel long-column chromatographic method was used to separate the organic compounds in the sample extract. Initially, the chromatographic method was tested on a synthetic multi-component test organic standard mixture (OSM), which contains groups of organic compounds, such as n-alkanes, alkanoic acids, benzothiazole, steroids, hydroxy/methoxy phenols, resin acids, polycyclic aromatic hydrocarbons (PAHs), polycarboxylic acids, secondary biogenics, and oxygenated-PAHs, comprising a total of 53 individual compounds. Compound recovery was typically high for the OSM. Next, extracts obtained from PM2.5 samples collected from Pittsburgh's ambient air were tested using silica gel column chromatography. The fractionation scheme produced well-defined separations of different organic compound classes for both the OSM and actual ambient sample extracts. In a case study, the fractionation process demonstrated its power by successfully separating overlapped sandaracopimaric acid and an unknown organic compound. The chemical fractionation method appears to generate highly selective markers for ambient air samples.