Multi-reflection photometric flow cell for use in flow injection analysis of estuarine waters Original Research Article

A multi-reflection flow cell suitable for flow analysis is described. Light from an LED is directed through an optical fibre into a silver coated capillary through a sidewall aperture, and emerges through a similar aperture 10 mm along the capillary after undergoing an estimated 19 reflections. This process provides a sensitivity enhancement of approximately 2.5 compared with a conventional z-cell of the same nominal path length. This enhancement is due to both the increased optical path length achieved by multiple reflection of the light beam through the sample, and minimization of physical dispersion by the use of a short, small internal diameter capillary as the flow cell. The optical design of this flow cell also minimizes the Schlieren effect. Optical and hydrodynamic characteristics of this multi-reflection cell have been evaluated using a series of bromothymol blue dye studies. Application of the flow cell to the determination of reactive phosphorus in estuarine waters with wide variation in salinity and refractive index is also described.