COMPENSATION OF THE SCHLIEREN EFFECT IN FLOW-INJECTION ANALYSIS BY USING DUAL-WAVELENGTH SPECTROPHOTOMETRY

The Schlieren effect in flow-injection analysis is critically examined. Effects of sample constitution, injection volume, coil lengths, flow-rates, confluent stream addition and temperature are studied and practical implications in flow-injection design with and without the stopped-flow approach are discussed. For Schlieren compensation, a diode-array spectrophotometer is used and non-specific absorbance subtraction is exploited: the incident light passes through the flowing sample, the emergent light is dispersed, the intensities of two selected monochromatic beams are measured simultaneously by separate detectors and real-time subtraction of the wavelength-independent noise is achieved. The sensitivity and measurement precision improve after application of the subtraction algorithm. The potential, limitations and practical applications of the method are discussed. © 1990.