Evaporative Light Scattering:  A Novel Detection Method for the Quantitative Analysis of Humic-like Substances in Aerosols

Abstract

The chemical composition of organic atmospheric aerosols is only poorly understood. Although a significant fraction of organic aerosols consists of humic-like substances (HULIS), only little is known about this class of compound, and accurate quantification remains difficult, partly due to the lack of appropriate standards. Here, evaporative light-scattering detection (ELSD) was applied for the first time to quantify water-soluble HULIS in aerosol particles smaller than 1 microm. This detection method was shown to be suitable for the quantification of compounds with unknown structures and lacking appropriate quantification standards. As compared to organic carbon determination of isolated HULIS, no organic carbon/organic mass (OC/OM) conversion factor needs to be applied with ELSD and therefore eliminates this significant uncertainty factor of the OC/OM method, which is frequently used to quantify HULIS. Solid-phase extraction and size-exclusion chromatography were applied to separate inorganic ions and low molecular weight compounds from HULIS before ELSD quantification. The ELSD itself provides an additional separation step where low volatility HULIS are separated from high volatility, small compounds. Electrospray ionization mass spectrometry was used to identify the molecular weight range of the compounds quantified with ELSD. The most intensive peaks were in the range of m/z 200-500, with some masses upto m/z800. We showed that UV detection using fulvic acid as surrogate quantification standard underestimates the HULIS concentration by a factor of 1.1 to 2.5, which is in agreement with earlier studies. During a 6 week winter 2005-2006 campaign at a suburban site near Zurich, Switzerland, an average of 1.1 microg/m(3) HULIS was found, which is about4-6% of the total particle mass smaller than 1 microm (PM1) and 10-35% of the organic matter in PM1.

Abundance and size distribution of HULIS in ambient aerosols at a rural site in South China

“…The isolated HULIS was quantified by injecting 20 or 60 mL of the aqueous solution into a HPLC system equipped with an evaporative light scattering detector (ELSD3300, Alltech, USA) (Emmenegger, Reinhardt, Hueglin, Zenobi, & Kalberer, 2007). No analytical column was used between the HPLC injector port and the ELSD detector since further separation of the HULIS fraction was not needed.…”

Chirality and the origin of atmospheric humic-like substances

“…The presence of inorganic salts in considerable amounts in the HULIS fraction was excluded earlier (Kiss et al, 2002;Emmenegger et al, 2007;Salma et al, 2007). However, it was demonstrated (Limbeck et al, 2005;Emmenegger et al, 2007;Stone et al, 2009) that some carboxylic acids and oxysubstituted aromatic compounds, e.g., succinic, adipic, hydroxybenzoic, lactic, trifluoroacetic, n-hexanoic, n-octanoic, cis-pinonic, phenylacetic, methylphthalic, cyclopentanedicarboxylic, butanedioic, heptanedioic, octanedioic, tricarballylic, benzenetricarboxylic and benzenetetracarboxylic acids, and some known biomass burning compounds including guaiacol, vanillin, acetovanillone and syringaldehyde (Saxena and Hildemann, 1996;Schauer et al, 2001;Decesari et al, 2006) could appear in the HULIS-containing eluent.…”

Advances in Integrated and Continuous Measurements for Particle Mass and Chemical Composition

“…WSOC species have been quantified for: (1) 98,112,113 ; (4) polycarboxylic acids (e.g., unsaturated aliphatic and aromatic species) by GC/MS and HPLC/UV 89 ; and (5) humic-like substances (HULIS) by HPLC/MS and HPLC/evaporative light scattering detection (ELSD). 114,115 Table 4 shows that the method precisions for these species also range from Ϯ5 to Ϯ30%. Interferences result from incomplete extraction efficiency, incompleteness of derivatization, contamination introduced during sample preparation, and chromatographic peak overlap and resolution.…”

“…86 Spectrometric detection (i.e., UV, IR) and nuclear magnetic resonance (NMR) 86,116,119,124,125 provide chemical structural information and quantification. Other quantification methods include ELSD, 115 electrospray ionization/MS (ESI/MS), laser desorption ionization/MS (LDI/ MS), 122,126 -130 pyrolysis GC/MS, 101 and capillary electrophoresis (CE). 116,131 Engling et al 105 analyzed water extracts for levoglucosan by IC/ECD instead of solvent extraction followed by derivatization with GC/MS detection (e.g., 104,107 ).…”

“…97,99,100 Of particular interest are HULIS and levoglucosan. These WSOC portions can be analyzed by IC/ECD, HPLC/PAD, HPLC/MS, and HPLC/ELSD 105,115,316 with a precision of Ϯ30%. PM 2.5 mass from TEOM, BAM, and the real-time total ambient mass sampler (RAMS) reported Ϯ10% precision.…”