SIMPLE FIBEROPTIC INTERFACE FOR ONLINE SUPERCRITICAL-FLUID EXTRACTION FOURIER-TRANSFORM INFRARED SPECTROMETRY

A simple and inexpensive fiber-optic interface for coupling a supercritical fluid extractor to a ET-IR spectrometer is described. The interface, based on chalcogenide (AsSeTe) fiber optics and a stainless steel union cross, is rugged up to pressures of 400 atm, has a spectral window from 5000 to 800 cm(-1), and is relatively easy to clean. It is shown that the SFE-FT-IR interface allows qualitative and quantitative information to be obtained from the extracts of real-world samples (caffeine in coffee and total petroleum hydrocarbons in soil, respectively) without the use of either a flow restrictor or a collection solvent. The determination of total petroleum hydrocarbons (TPH) in soils by static on-line SFE-FT-IR yields values in good agreement with both off-line SFE and Soxhlet extraction. The detection limit for TPH, using a 48-s scan time, was determined to be 1.6 ppm (wt TPH/wt sample). The linear dynamic range of calibration for the TPH determinations was greater than 3 orders of magnitude.