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A Novel Type of Tri-Colour Light-Emitting-Diode-Based Spectrometric Detector for Low-Budget Flow-Injection Analysis

View Article: PubMed Central

ABSTRACT

In this paper we describe a low-cost spectrometric detector that can be easily assembled in a laboratory for less than €80 with a minimal number of optical components and which has proved sensitive and flexible enough for real-life applications. The starting point for the idea to construct this small, compact low-cost spectrometric detector was the decision to use a tri-colour light-emitting diode (LED) of the red-green-blue (RGB) type as a light source with the objective of achieving some flexibility in the selection of the wavelength (430 nm, 565 nm, 625 nm) but avoiding the use of optical fibres. Due to the dislocation of the emitters of the different coloured light, the tri-colour LED-based detector required an optical geometry that differs from those that are described in literature. The proposed novel geometry, with a coil-type glass flow-through cell with up to four ascending turns, proved useful and fit for the purpose. The simplicity of the device means it requires a minimal number of optical components, i.e., only a tri-colour LED and a photoresistor. In order to make a flow-injection analysis (FIA) with the spectrometric detector even more accessible for those with a limited budget, we additionally describe a low-cost simplified syringe-pump-based FIA set-up (€625), the assembling of which requires no more than basic technical facilities. We used such a set-up to test the performance of the proposed spectrometric detector for flow-injection analyses. The tests proved its suitability for real-life applications. The design procedures are also described.

No MeSH data available.


Electronic circuitry for powering the tri-colour LED (left) and the photometric detection system (right).
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f13-sensors-07-00166: Electronic circuitry for powering the tri-colour LED (left) and the photometric detection system (right).

Mentions: In order to select the appropriate optical geometry for the spectrometric detector the optical beams emerging from a tri-colour LED were examined a distance of 3 mm away from the LED's epoxy body. Spots with a circular shape were observed for the green and red light. Both had an area of highest light intensity with a diameter of approximately 8 mm; however, even at this relatively small distance the centres of the two circles were 3 mm apart. The beam of blue light had an elliptical shape. The ellipse with the highest blue-light intensity was 11 mm long and was perpendicular to the line in which the spots of the red and the green light lay. It was clear that all three beams overlap in a circular region with a diameter of 5–6 mm. In order to use the light from all three light emitters effectively and to obtain an appropriate light path length, but to avoid an excessively large internal volume of the flow-through cell, we decided to test a novel glass coil-type flow-through cell and the optical geometry of the spectrometric detector, which is presented in Figure 1. The detector can be easily constructed in a laboratory. The procedure for designing the coil-type flow-through cell and the assembling of the electronic circuitry are described in the Experimental section, 3.1. The design containing an unreferenced LED source and the signal linearly related to the transmittance was used. The emitters of the light of three different colours are switched on separately. The possibility to regulate their luminous intensity using three 10-kΩ potentiometers (Figure 13) proved essential for achieving the optimal sensitivity of the spectrometric detector under different experimental conditions. Three prototyped coil-type flow-through cells were selected for further tests. Their main characteristics were defined and are summarized in Table 1.


A Novel Type of Tri-Colour Light-Emitting-Diode-Based Spectrometric Detector for Low-Budget Flow-Injection Analysis
Electronic circuitry for powering the tri-colour LED (left) and the photometric detection system (right).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756699&req=5

f13-sensors-07-00166: Electronic circuitry for powering the tri-colour LED (left) and the photometric detection system (right).
Mentions: In order to select the appropriate optical geometry for the spectrometric detector the optical beams emerging from a tri-colour LED were examined a distance of 3 mm away from the LED's epoxy body. Spots with a circular shape were observed for the green and red light. Both had an area of highest light intensity with a diameter of approximately 8 mm; however, even at this relatively small distance the centres of the two circles were 3 mm apart. The beam of blue light had an elliptical shape. The ellipse with the highest blue-light intensity was 11 mm long and was perpendicular to the line in which the spots of the red and the green light lay. It was clear that all three beams overlap in a circular region with a diameter of 5–6 mm. In order to use the light from all three light emitters effectively and to obtain an appropriate light path length, but to avoid an excessively large internal volume of the flow-through cell, we decided to test a novel glass coil-type flow-through cell and the optical geometry of the spectrometric detector, which is presented in Figure 1. The detector can be easily constructed in a laboratory. The procedure for designing the coil-type flow-through cell and the assembling of the electronic circuitry are described in the Experimental section, 3.1. The design containing an unreferenced LED source and the signal linearly related to the transmittance was used. The emitters of the light of three different colours are switched on separately. The possibility to regulate their luminous intensity using three 10-kΩ potentiometers (Figure 13) proved essential for achieving the optimal sensitivity of the spectrometric detector under different experimental conditions. Three prototyped coil-type flow-through cells were selected for further tests. Their main characteristics were defined and are summarized in Table 1.

View Article: PubMed Central

ABSTRACT

In this paper we describe a low-cost spectrometric detector that can be easily assembled in a laboratory for less than €80 with a minimal number of optical components and which has proved sensitive and flexible enough for real-life applications. The starting point for the idea to construct this small, compact low-cost spectrometric detector was the decision to use a tri-colour light-emitting diode (LED) of the red-green-blue (RGB) type as a light source with the objective of achieving some flexibility in the selection of the wavelength (430 nm, 565 nm, 625 nm) but avoiding the use of optical fibres. Due to the dislocation of the emitters of the different coloured light, the tri-colour LED-based detector required an optical geometry that differs from those that are described in literature. The proposed novel geometry, with a coil-type glass flow-through cell with up to four ascending turns, proved useful and fit for the purpose. The simplicity of the device means it requires a minimal number of optical components, i.e., only a tri-colour LED and a photoresistor. In order to make a flow-injection analysis (FIA) with the spectrometric detector even more accessible for those with a limited budget, we additionally describe a low-cost simplified syringe-pump-based FIA set-up (€625), the assembling of which requires no more than basic technical facilities. We used such a set-up to test the performance of the proposed spectrometric detector for flow-injection analyses. The tests proved its suitability for real-life applications. The design procedures are also described.

No MeSH data available.