ONLINE NONMETAL DETECTION FOR ARGON SUPERCRITICAL-FLUID EXTRACTION USING INDUCTIVELY-COUPLED PLASMA OPTICAL-EMISSION SPECTROSCOPY

This paper describes the development of a solventless instrumental met hod for determining organic contaminants in soil by coupling argon sup ercritical fluid extraction (SFE) to inductively coupled plasma atomic emission spectroscopy (ICP-AES), In this method, organic compounds ar e first extracted by Ar SFE, transferred to the ICP directly in the su percritical (SC) argon, fragmented in the plasma, and then determined via their nonmetal atomic emissions. Supercritical Ar is superior to S C CO2 for use in ICP-AES because it overcomes the disadvantages of pla sma blowout, noisy baselines, and CO2 interference in the determinatio n of carbon. All instruments employed were commercially available, and the interface between the SFE and the torch of the ICP consisted of a simple glass capillary tube. Four nonmetals, C, S, P, and Si, were se lected for this preliminary study. The selectivities obtained for thes e nonmetals, referenced to carbon, were found to be 345, 38 000, and 1 400 for sulfur, phosphorus, and silicon, respectively. With the except ion of carbon, the mass detection limits are in the range of 0.06-1.8 mu g. For this work, the mass detection limit of carbon is 66 mu g and is limited by the smallest aliquot of material that can be injected b y syringe. Finally, total petroleum hydrocarbons (TPHs) were determine d in two ''real world'' contaminated soil samples via the carbon emiss ion at 247.9 nm, Dodecane was used as the standard reference compound because its response was found to be similar to other petroleum hydroc arbons (e.g., kerosene, gasoline, no. 1 fuel oil, and no. 2 fuel oil). Additionally, it was found necessary to add a small amount (i.e., 250 mg) of drying agent to the SFE vessel in order to prevent the plasma from extinguishing from the extracted water. The results of the on-lin e Ar SFE/ICP-AES determinations of TPH in the two samples agreed well. with those obtained from conventional off-line CO2 SFE and off-line A r SFE.