Ultrasonic nebulization for the elemental analysis of microgram-level samples with offline aerosol mass spectrometry

Abstract

Abstract. The elemental composition of organic material in environmental samples – including atmospheric organic aerosol, dissolved organic matter, and other complex mixtures – provides insights into their sources and environmental processing. However, standard analytical techniques for measuring elemental ratios typically require large sample sizes (milligrams of material or more). Here we characterize a method for measuring elemental ratios in environmental samples, requiring only micrograms of material, using a small-volume nebulizer (SVN). The technique uses ultrasonic nebulization of samples to generate aerosol particles (100–300 nm diameter), which are then analyzed using an aerosol mass spectrometer (AMS). We demonstrate that the technique generates aerosol from complex organic mixtures with minimal changes to the elemental composition of the organic material and that quantification is possible using internal standards (e.g., NH415NO3). Sample volumes of 2–4 µL with total solution concentrations of at least 0.2 g L−1 form sufficient particle mass for elemental ratio measurement by the AMS, despite only a small fraction (∼ 0.1 %) of the sample forming fine particles after nebulization (with the remainder ending up as larger droplets). The method was applied to aerosol filter extracts from the field and laboratory, as well as to the polysaccharide fraction of dissolved organic matter (DOM) from the North Pacific Ocean. In the case of aerosol particles, the mass spectra and elemental ratios from the SVN–AMS agree with those from online AMS sampling. Similarly, for DOM, the elemental ratios determined from the SVN–AMS agree with those determined using combustion analysis. The SVN–AMS provides a platform for the rapid quantitative analysis of the elemental composition of complex organic mixtures and non-refractory inorganic salts from microgram samples with applications that include analysis of aerosol extracts and terrestrial, aquatic, and atmospheric dissolved organic matter.

UV/Vis and IRMPD Spectroscopic Analysis of the Absorption Properties of Methylglyoxal Brown Carbon

“…This effective quantum yield is smaller than the one measured in Aiona et al, largely due to the differences in the measured MAC. Here, the sample was made using a slow-aging method and the mass of the material was estimated using the SVN with the AMS (SVN-AMS) . This gives absorption cross sections (Figure ) that are only a factor of 2–2.5 times larger than in Zhao et al but a factor of 20–25 times larger than those in Aiona et al and a factor of 80 times larger than in Harrison et al ,, Our results are likely similar to those of Zhao et al because that study also used slow-aging reactions.…”

“…Here, the SVN-AMS was used to estimate the organic mass and the factor of 2 difference may be due to an underestimation of the organic mass due to either the volatility of some components or a difference in relative ionization efficiency from the standard 1.4 used for ambient aerosol. 28,29 Alternatively, a slightly higher yield of chromophores may have been obtained here.…”

“…Data for absorption cross sections were collected from the dilute initial solutions for photolysis experiments with initial organic concentrations measured with the small volume nebulizer-aerosol mass spectrometer (SVN-AMS). 27,28 For analysis with the SVN-AMS, an internal standard (NH 4 15 NO 3 ) is mixed with the solution and nebulized into the AMS. The AMS provides quantification of both the total organic and the internal standard.…”

“…The wavelength-dependent mass absorption cross sections (MAC) for the bulk solutions were calculated using where A 10 (λ) is the absorbance (base-10), b is the path length (1 cm), and C org is the concentration of the photo-active organic in the solution (g cm –3 ). Data for absorption cross sections were collected from the dilute initial solutions for photolysis experiments with initial organic concentrations measured with the small volume nebulizer-aerosol mass spectrometer (SVN-AMS). , For analysis with the SVN-AMS, an internal standard (NH 4 15 NO 3 ) is mixed with the solution and nebulized into the AMS. The AMS provides quantification of both the total organic and the internal standard.…”

Equal abundance of summertime natural and wintertime anthropogenic Arctic organic aerosols

“…Therefore, the total OA concentration is not affected by the collection efficiency. All extracted aerosol species are expected to be internally mixed in the nebulized particles, so the offline AMS collection efficiency should be the same for all identified OA factors 91,92 .…”