Detection of aerosol formation in the effluent of a supercritical fluid chromatograph

Supercritical fluid techniques continue to grow in importance in analytical chemistry, especially supercritical fluid chromatography. Accompanying this growth is the development of postcolumn detection methods, including flame ionization detection, inductively coupled plasma emission, mass spectrometry, and supersonic jet spectroscopy. In each of these detection methods, the behavior of the fluid at the point of decompression especially in regard to nucleation processes, can severely affect the performance of the detector. Solute aggregation is the major contributor to the spiking which has been observed with flame ionization detection, but, as the authors discuss later in this paper, erratic spitting of large aerosol droplets can occur with extended restrictors and will also produce noise spikes. However, even fine aerosol mists can severely interfere with spectroscopic detection, not only increasing the noise level but also inhomogeneously broadening spectral lines; thus the characterization of aerosol formation has been particularly important to their investigation of supersonic jet spectroscopy with supercritical fluid carriers. They report here the conditions for aerosol formation in the effluent jet, as monitored by laser-light scattering, for five fluids, which cover a wide range of critical constants and chemical properties.