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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.


Linearity of the detector's responses in the range of the blue light (B-LED) and the red light (R-LED) for cells 10a, 11a and 12 at minimum (min) and maxim (max) light intensity.
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f3-sensors-07-00166: Linearity of the detector's responses in the range of the blue light (B-LED) and the red light (R-LED) for cells 10a, 11a and 12 at minimum (min) and maxim (max) light intensity.

Mentions: A stock Solution I (Experimental section 3.3) proved to be a suitable combination of food dies, E102, E110 and E131, for the detector's performance test in the range of the blue and red light because for this solution a spectrum with two wide, well-separated absorption peaks of similar height with absorption maxima at 418 and 662 nm, respectively, is obtained. For the test of the linearity the stock solution was further diluted with 20 mmol/L of ammonium acetate. The measurements were performed with all three coil-type flow-through cells against a 20-mmol/L ammonium acetate solution as a blank. The results are presented in Figure 3. The absorbencies in the range of the blue and red light are linearly related to the concentration up to the absorbance value of 0.45. This result is very similar to that obtained with the green light. The highest sensitivity was achieved with flow-through cell 12, and it was very similar for both the blue and red light. However, it should be pointed out that with this cell the spectrometric detector was at the limit of its ability in the range of the blue light and only the maximum light intensity with the highest amplification setting of the operational amplifier produced 100% transmittance. This is not at all surprising if we take into account the tri-colour LED's characteristics. The maximum luminous intensities reported by the producer are 90 mcd for red, 70 mcd for green and 12.5 mcd for each of the two blue light emitters. Consequently, an experiment in the blue-light range was not possible at all with cell 10a. This coil's diameter is obviously too small, preventing it from catching enough light to achieve 100% transmittance for the blank. Even in the range of the red light there was only just enough light due to the fact that the lines obtained for the 10a cell at the maximum and minimum light intensities nearly overlap. Here, again, the detector with flow-through cell 11a performed moderately well. Very similar responses were obtained in the blue-light range and at the minimum intensity of the red light.


A Novel Type of Tri-Colour Light-Emitting-Diode-Based Spectrometric Detector for Low-Budget Flow-Injection Analysis
Linearity of the detector's responses in the range of the blue light (B-LED) and the red light (R-LED) for cells 10a, 11a and 12 at minimum (min) and maxim (max) light intensity.
© Copyright Policy
Related In: Results  -  Collection

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

f3-sensors-07-00166: Linearity of the detector's responses in the range of the blue light (B-LED) and the red light (R-LED) for cells 10a, 11a and 12 at minimum (min) and maxim (max) light intensity.
Mentions: A stock Solution I (Experimental section 3.3) proved to be a suitable combination of food dies, E102, E110 and E131, for the detector's performance test in the range of the blue and red light because for this solution a spectrum with two wide, well-separated absorption peaks of similar height with absorption maxima at 418 and 662 nm, respectively, is obtained. For the test of the linearity the stock solution was further diluted with 20 mmol/L of ammonium acetate. The measurements were performed with all three coil-type flow-through cells against a 20-mmol/L ammonium acetate solution as a blank. The results are presented in Figure 3. The absorbencies in the range of the blue and red light are linearly related to the concentration up to the absorbance value of 0.45. This result is very similar to that obtained with the green light. The highest sensitivity was achieved with flow-through cell 12, and it was very similar for both the blue and red light. However, it should be pointed out that with this cell the spectrometric detector was at the limit of its ability in the range of the blue light and only the maximum light intensity with the highest amplification setting of the operational amplifier produced 100% transmittance. This is not at all surprising if we take into account the tri-colour LED's characteristics. The maximum luminous intensities reported by the producer are 90 mcd for red, 70 mcd for green and 12.5 mcd for each of the two blue light emitters. Consequently, an experiment in the blue-light range was not possible at all with cell 10a. This coil's diameter is obviously too small, preventing it from catching enough light to achieve 100% transmittance for the blank. Even in the range of the red light there was only just enough light due to the fact that the lines obtained for the 10a cell at the maximum and minimum light intensities nearly overlap. Here, again, the detector with flow-through cell 11a performed moderately well. Very similar responses were obtained in the blue-light range and at the minimum intensity of the red light.

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.