Abstract
A flame infrared emission (FIRE) gas chromatography (GC) detector for organofluorine and organochlorine compounds has been developed and evaluated. The element-specific GC-FIRE detector makes use of a beamsplitter to divide the source radiation into two optical paths. The divided radiation passes through appropriate notch filters to isolate the background and analyte emission, which are each monitored by separate lead selenide detectors that form part of a Wheatstone bridge network. The output from the Wheatstone bridge is fed into the differential mode (A-B) input of a lock-in amplifier (LIA). In the chlorine mode of operation, a 3.7-μm optical notch filter is used in the analytical channel to isolate a portion of the HCl emission that results when organochlorine compounds are combusted in the hydrogen/air flame. In the fluorine mode of operation, a 2.35-μm optical notch filter in combination with a 2.55-μm short-pass filter is used to isolate a portion of the HF emission that results when organofluorine compounds are combusted. With the use of the dual-channel system, selectivity ratios of at least 760 (F) and 100 (Cl) were obtained, respresenting improvements by factors of about 104 (F) and 30 (Cl) in comparison with results from the single-channel mode of operation. With the use of Freon-113® (C<sub>2</sub>Cl<sub>3</sub>F<sub>3</sub>) as a representative analyte, detection limits in both the chlorine- and fluorine-selective modes were 200 ng s<sup>−1</sup>, representing improvements by factors of about 9.5 (F) and 4.5 (Cl), in comparison with results from the single-channel mode of operation.
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