New methods for measurement of chemical composition

Online, real-time analysis of water-soluble phosphate ions

The measurement of soluble (bioavailable) phosphate is important to understand the effect of aerosol input into phosphorus-limited marine ecosystems.
Most measurements of atmospheric phosphate ions based on filter sampling are measured with a long time resolution typically of 1 to 3 days, which can introduce mixing artifacts or miss rapid changes in phosphate solubility that can occur, for instance, due to acidification of desert dust. To alleviate these issues, we developed an online, real-type analytical method for measurement of water-soluble reactive phosphate (SRP) in atmospheric aerosols based on direct particle capture into liquid and spectrophotometric detection of complexes formed by induced chemical reaction.

Figure 1: Schematic diagram and photograph of particle-in-liquid sampler with liquid waveguide capillary cell (PILS-LWCC) for online measurements of phosphate ions. From Violaki et al. doi:10.1021/acs.analchem.6b01264, 2016.

Solvent-elimination infrared spectroscopy

Some substrates onto which atmospheric particulate matter is collected are effectively opaque to infrared radiation. A common approach for analysis is to transfer the mass from the substrate to an optical element via solvent extraction. However, solvents interfere with spectroscopic analysis and must be evaporated prior to examination, and the remaining analyte can dry in a undesirable, non-uniform configurations. For this purpose, we developed a technique for rapid solvent elimination and uniform coating of a semiconducting crystal (ZnSe) by electrospray deposition for analysis by sensitive, multireflection (attenuated total reflectance) ATR-FTIR. The coating created by the spraying can be analyzed in the thin-film limit by the ATR-FTIR, which produces transmission-mode-like spectra.

Figure 2: Electrospray apparatus. Photograph and diagram on left from Arangio et al., Appl. Spectrosc., doi:10.1177/0003702818821330, 2019.

Selected references