DETERMINATION OF OPTIMAL STORAGE-CONDITIONS FOR PARTICLE SAMPLES

Results are presented from laboratory studies on how to store particle samples to preserve them for chemical, physical, and biologic testing. Surrogate samples for power plant plume fly ash were created by using electrostatic precipitator (ESP) hopper ash. Particles of diameters less than 10 μm were suspended and mixed with three poly-cyclic aromatic hydrocarbons (PAH), one nitro-PAH, salt, and sulfuric acid. The particle mixture was then collected on filters to create surrogate samples. Samples were stored for periods of 30 and 120 days at either 20 or −79 ± 1 °C as well as under a set of variable conditions of temperature, light, and humidity. Gas chromatography/mass spectrometry and scanning electron microscopy with energy dispersive analysis were used to characterize changes in organic and elemental composition, particle size distribution, and particle morphology. Preservation of organic compounds in the samples was best achieved when the samples were packaged in Teflon-wrapped glass dishes. Both storage temperature and duration of storage can influence sample stability. In many cases storage at −79 °C provided statistically significant enhancement of organic compound stability after 120 days compared to storage at 20 °C. Particle agglomeration in some samples was suggested by microscopy results. Sulfuric acid had a deleterious effect on two of the spiked PAH. Considering all factors, the most favorable storage conditions were −79 °C in the dark. Under these conditions, loss of the lightest PAH (fluorene) was minimized; the heaviest PAH (chrysene) was stable for at least 120 days. © 1990, American Chemical Society. All rights reserved.