Profiling Water-Soluble Organic Matter from Urban Aerosols Using Comprehensive Two-Dimensional Liquid Chromatography

Abstract

Comprehensive two-dimensional liquid chromatography (LC£LC) coupled with a diode array detector (DAD) has been used for the first time to investigate chemical heterogeneity and map the hydrophobicity versus molecular weight distribution of the most hydrophobic acid fractions in water-soluble organic matter (WSOM) from fine atmospheric aerosols collected over different seasons at a urban location. The use of LC£LC-DAD, combining the use of two independent separation mechanisms (per aqueous liquid chromatography [PALC] versus sizeexclusion chromatography [SEC]), has shown a great potential for unraveling and resolving the heterogeneity of WSOM, further providing a deeper insight into how size-distinguished aerosol WSOM fractions differ in hydrophobicity during different seasonal events. The combination of PALC£SEC-DAD data with an already proposed data treatment procedure revealed that the WSOM samples collected during warm seasons are enriched in aliphatic structures, while those collected during colder seasons exhibit a higher degree of structures with conjugation of p-bonds (e.g., aromatics) alongside aliphatic structures.

Comparative study of atmospheric water-soluble organic aerosols composition in contrasting suburban environments in the Iberian Peninsula Coast

“…One field blank was collected in each sampling period in order to correct for ambient background PM 2.5 and PM 10 mass, total carbon (TC), water-soluble organic carbon (WSOC), total nitrogen (TN), isotopic (δ 13 C and δ 15 N), and water-soluble trace metals levels. This sampling procedure is similar to those adopted in previous studies of advanced structural characterization of aerosol WSOM from low sample size groups Duarte et al, 2017b;Duarte et al 2005;Duarte et al, 2007;Duarte et al, 2008;Lopes et al, 2015;Matos et al, 2017;Matos et al, 2015b). Additional details on aerosol sampling procedure in Aveiro and A Coruña are available in section S1, in SI.…”

Multidimensional Analytical Characterization of Water-Soluble Organic Aerosols: Challenges and New Perspectives

“…In these studies, LC × LC, combining the use of two independent separation mechanisms (per aqueous liquid chromatography (PALC) vs. size-exclusion chromatography (SEC)), was coupled with a diode array (DAD) and fluorescence (FL) detectors to map the hydrophobicity vs. molecular weight distribution of the most hydrophobic acid fractions in WSOM and alkaline-soluble organic matter from fine urban aerosols collected over different seasons. As shown in Figure 2a,b for samples collected during summer and winter, the PALC × SEC method allowed the separation of WSOM hydrophobic acid samples into several fractions, with the UV absorption contour plots displaying different elution patterns [27]. Apparently, the obtained fractions exhibit different molar mass distributions and chemical characteristics in terms of hydrophobicity between the two different seasons (Figure 2c,d).…”

“…For example, LC × LC coupled to electrospray ionization ToF-MS (ESI-ToF-MS) has been applied for the identification and quantification of carboxylic acids in rural and urban aerosol samples [57]. LC × LC has also been employed for unraveling the complexity of WSOM from fine urban atmospheric aerosols and identify its seasonal patterns [27,58]. In these studies, LC × LC, combining the use of two independent separation mechanisms (per aqueous liquid chromatography (PALC) vs. size-exclusion chromatography (SEC)), was coupled with a diode array (DAD) and fluorescence (FL) detectors to map the hydrophobicity vs. molecular weight distribution of the most hydrophobic acid fractions in WSOM and alkaline-soluble organic matter from fine urban aerosols collected over different seasons.…”

“…Several procedures and methodologies have been developed to study the chemical composition of the aerosol WSOM [8][9][10][11]23,[27][28][29][30][31][32][33][34]. These studies are usually carried out using a combination of total organic carbon analysis, isolation and fractionation procedures, and characterization of molecular fragments and intermolecular bonds by different analytical techniques.…”

Referee Comments

“…Regarding the use of UV-Vis, fluorescence and 1H-NMR spectroscopies for the characterization of properties of HULIS from atmospheric aerosols there are very recent references that also shed some light on this matter and they should be considered when discussing the results of the submitted paper. For the case UV-Vis spectroscopy there is a reference (Matos et al, 2015b) where the authors used comprehensive two-dimensional liquid chromatography (LCxLC) coupled with a diode array detector (DAD) in order to assessing the chemical heterogeneity and mapping the hydrophobicity vs. molecular weight distribution of the most hydrophobic acid fractions in WSOC (which the authors consider as water soluble organic matter, WSOM) from fine atmospheric aerosols collected over different seasons at a urban location. For the case of fluorescence spectroscopy there are two important recent references (Matos et al, 2015a;Paula et al, 2016).…”