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.

Miniaturized optical chemosensor for flow-based assays

“…The flow inlet and outlet are drilled through the plastic body of the LED detector (see Fig. 1c and d), generating the so-called flow-cell within LED [22]. The second LED operating as a light emitter is utilized without any mechanical modification.…”

A method for determination of ammonia in air using oxalic acid-impregnated cellulose filters and fluorimetric detection

“…The major source of contamination in the laboratory is frequently the operator; the ammonia concentration in expired air can be as high as one hundred parts per billion. 35 Limits of detection can be improved by using a longer sampling time, which increases the analytical signal, albeit at the expense of sampling frequency. Nonetheless, the results obtained here demonstrate that environmental ammonia contamination can be successfully controlled and avoided.…”