Measurement of mercaptans in gasoline

Abstract

In an r-FIA single-line manifold, 10-μl portions of 5,5′-dithiobis (2-nitrobenzoic acid) and 2% (v/v) ethylenediamine in 80 ∶ 20 inethanol: acetone are injected from pressurized containers via high-speed on/off valves into a flowing gasoline stream. The reaction product, 2-nitro-5-mercaptobenzoate, is detected optically at 412 nm after a reaction time of ∼15s. The system is intended for the measurement of mercaptans in the 0–2 mM (0–64 ppm S) concentration range. The response for C1–C10n-mercaptans ranges from 0.766–0.159 mAU/mM, the response to C1–C5n-mercaptans is 630 mAU/mM (±18.5% RSD). The response ratio of C1 and C5 mercaptans is 1 ∶ 0.653. The system permits extreme conservation of reagents; only 10 μl of each reagent is consumed per determination.