Instrumentation is reported for rapid, on-line quantitative analysis of the gaseous effluent from a heterogeneously catalyzed reaction. Absorption bands over the mid-infrared (IR) range 4000-580 cm(-1) have been used to quantify, in less than 2 min, the major gaseous products of the hydrogenation of carbon monoxide (Fischer-Tropsch synthesis) using partial least squares (PLS) methodology. The fast analysis capability of the IR technique coupled to a single channel microreactor enables the approach of a Fischer-Tropsch catalyst to steady-state to be investigated by sampling the products every 2 min for 3 h on-stream. Coupling IR spectroscopy and chemometrics in this manner will allow a wide range of heterogeneously catalyzed reactions to be analyzed in very short times, a key requisite for high throughput catalyst testing. (C) 2003 Elsevier B.V. All rights reserved.