Raman spectroscopy of samples collected by the Nano-ID Select: a new quasi on-line analytical technique to identify and quantify aerosol particles.

Raman spectroscopy has been performed on sample collected by the Nano-ID Select using an Ocean Optics portable handheld Raman Spectrometer. This is a useful technique for the characterisation of many organic and inorganic compounds, for example Carbon Nanotubes, which may be present in an aerosol sample.  The Raman spectroscopic technique involves directing a monochromatic light source (such as a laser) onto a sample and detecting the scattered light. Most of the light is scattered elastically (known as Rayleigh scatter), but a small fraction is scattered inelastically (Raman scatter). Raman scatter involves the interaction of incident electromagnetic radiation with the vibrational frequencies of the molecule (nm) to cause a shift in the frequency of the scattered light away from the excitation wavelength (nex ± n m).
This technique does not require any special sample preparation and Raman spectra can be obtained in a few minutes. The Raman data can be applied to identify and quantify the mass-size distribution of specific compounds in a relatively short time.

Raman spectrometry can provide a wealth of information about the chemical nature of aerosol particles. For example, the Raman spectra of TiO2 particles changes depending on the size of particles present, and therefore can be used reveal difference in the nature of the TiO2 particles, for example changes in the crystal structure. Figure 7.1 shows a collection of Raman Spectra taken using an Ocean Optics portable Raman system from size-fractionated samples of TiO2 aerosol particles collected using a Nano-ID Select. The four peaks clearly observed at ~150, 402, 520, and 643/cm are characteristic of TiO2 particles.

Figure 7.1: Raman spectra of TiO2 aerosol particles sampled using a Nano-ID Select. The spectra were obtained using an Ocean Optics portable Raman system without requiring any sample preparation.

The numbered stages in figure 7.1 correspond to the following particle size fractions: