title: Flow cell within an LED: a proposal for an optical absorption detector.
abstract: Droplets formed at the tip of a tube under the same conditions possess extreme uniformity of form, volume and weight. These properties of liquid drop formation have been known for a long time and consequently many applications for the drop have been found in instrumentation and chemical analysis methods. In the present paper, we report on the analytical use of a dynamic LED-based flow-through optical absorption detector with optical path length controlled by continuous dropping of a solution. This arrangement consists of a flow cell built within a high-intensity red LED (lambda(max) = 630 nm). The feasibility of the detector is demonstrated by colorimetric determination of methylene blue, and ammonium by Berthelot's reaction, in a flow-injection system. For ammonium, the reaction forms a blue dye (indophenol) with a maximum absorption at 630-650 nm. The detection limit, considered as 3 times the signal of the blank, is better than 125 microg l(-1). The small flow cell represents a good combination of optical path length, low volume and fast washout. This detector can be used advantageously in automated methods and can represent a solution to problems of optical detection involving gas bubbles and precipitation of particles in turbidimetric applications.
authors.affiliation: Department of Analytical Chemistry, Institute of Chemistry, UNESP, CP 355, CEP 14801-970, Araraquara, SP, Brazil.
authors.forename: Cássia
authors.initials: C
authors.lastname: Ugucione
authors.forename: Arnaldo Alves
authors.initials: AA
authors.lastname: Cardoso