Abstract
This study describes a continuous flow pro- cedure for monitoring atmospheric sulfur dioxide using a planar gas permeation denuder (GPD) and a fiber optic spectrometer. When gaseous samples are directed through a GPD which consists of a gas-perme- able membrane of poly(vinylidene) difluoride and two perspex blocks with engraved channels of mirror image, the fraction of sulfur dioxide passing the membrane is absorbed in a flowing stream of 5.0� 10 � 4 mol L � 1 5,5 0 -dithiobis(2,2 0 -dinitrobenzoic acid) (DTNB) in 0.025 mol L � 1 phosphate buffer of pH 7.0, and reacts with DTNB to yield a yellow product. This product is monitored spectrophotometrically at 410 nm with a miniature charge-coupled device (CCD) fiber optic spectrometer. The analytical range of sulfur diox- ide is easily adjusted via the flow rate of DTNB solu- tion, normally from 200 ppb to 94 ppm (v=v). The procedure is hardly interfered with by coexisting metal and non-metal species, except for hydrogen sulfide in the atmosphere. The error caused by hydrogen sulfide at a sulfur dioxide level (in ppm) of 2% is less than � 10%. With the proposed procedure, the result for a mimetic air sample is very close to that of the ultra- violet fluorescence method.
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